// SPDX-License-Identifier: GPL-2.0
#ifndef NO_BCACHEFS_FS

#include "bcachefs.h"
#include "alloc_foreground.h"
#include "bkey_buf.h"
#include "btree_update.h"
#include "buckets.h"
#include "clock.h"
#include "error.h"
#include "extents.h"
#include "extent_update.h"
#include "fs.h"
#include "fs-io.h"
#include "fsck.h"
#include "inode.h"
#include "journal.h"
#include "io.h"
#include "keylist.h"
#include "quota.h"
#include "reflink.h"

#include <linux/aio.h>
#include <linux/backing-dev.h>
#include <linux/falloc.h>
#include <linux/migrate.h>
#include <linux/mmu_context.h>
#include <linux/pagevec.h>
#include <linux/rmap.h>
#include <linux/sched/signal.h>
#include <linux/task_io_accounting_ops.h>
#include <linux/uio.h>
#include <linux/writeback.h>

#include <trace/events/bcachefs.h>
#include <trace/events/writeback.h>

static inline bool bio_full(struct bio *bio, unsigned len)
{
	if (bio->bi_vcnt >= bio->bi_max_vecs)
		return true;
	if (bio->bi_iter.bi_size > UINT_MAX - len)
		return true;
	return false;
}

static inline struct address_space *faults_disabled_mapping(void)
{
	return (void *) (((unsigned long) current->faults_disabled_mapping) & ~1UL);
}

static inline void set_fdm_dropped_locks(void)
{
	current->faults_disabled_mapping =
		(void *) (((unsigned long) current->faults_disabled_mapping)|1);
}

static inline bool fdm_dropped_locks(void)
{
	return ((unsigned long) current->faults_disabled_mapping) & 1;
}

struct quota_res {
	u64				sectors;
};

struct bch_writepage_io {
	struct closure			cl;
	struct bch_inode_info		*inode;

	/* must be last: */
	struct bch_write_op		op;
};

struct dio_write {
	struct completion		done;
	struct kiocb			*req;
	struct mm_struct		*mm;
	unsigned			loop:1,
					sync:1,
					free_iov:1;
	struct quota_res		quota_res;
	u64				written;

	struct iov_iter			iter;
	struct iovec			inline_vecs[2];

	/* must be last: */
	struct bch_write_op		op;
};

struct dio_read {
	struct closure			cl;
	struct kiocb			*req;
	long				ret;
	bool				should_dirty;
	struct bch_read_bio		rbio;
};

/* pagecache_block must be held */
static int write_invalidate_inode_pages_range(struct address_space *mapping,
					      loff_t start, loff_t end)
{
	int ret;

	/*
	 * XXX: the way this is currently implemented, we can spin if a process
	 * is continually redirtying a specific page
	 */
	do {
		if (!mapping->nrpages)
			return 0;

		ret = filemap_write_and_wait_range(mapping, start, end);
		if (ret)
			break;

		if (!mapping->nrpages)
			return 0;

		ret = invalidate_inode_pages2_range(mapping,
				start >> PAGE_SHIFT,
				end >> PAGE_SHIFT);
	} while (ret == -EBUSY);

	return ret;
}

/* quotas */

#ifdef CONFIG_BCACHEFS_QUOTA

static void bch2_quota_reservation_put(struct bch_fs *c,
				       struct bch_inode_info *inode,
				       struct quota_res *res)
{
	if (!res->sectors)
		return;

	mutex_lock(&inode->ei_quota_lock);
	BUG_ON(res->sectors > inode->ei_quota_reserved);

	bch2_quota_acct(c, inode->ei_qid, Q_SPC,
			-((s64) res->sectors), KEY_TYPE_QUOTA_PREALLOC);
	inode->ei_quota_reserved -= res->sectors;
	mutex_unlock(&inode->ei_quota_lock);

	res->sectors = 0;
}

static int bch2_quota_reservation_add(struct bch_fs *c,
				      struct bch_inode_info *inode,
				      struct quota_res *res,
				      u64 sectors,
				      bool check_enospc)
{
	int ret;

	mutex_lock(&inode->ei_quota_lock);
	ret = bch2_quota_acct(c, inode->ei_qid, Q_SPC, sectors,
			      check_enospc ? KEY_TYPE_QUOTA_PREALLOC : KEY_TYPE_QUOTA_NOCHECK);
	if (likely(!ret)) {
		inode->ei_quota_reserved += sectors;
		res->sectors += sectors;
	}
	mutex_unlock(&inode->ei_quota_lock);

	return ret;
}

#else

static void bch2_quota_reservation_put(struct bch_fs *c,
				       struct bch_inode_info *inode,
				       struct quota_res *res)
{
}

static int bch2_quota_reservation_add(struct bch_fs *c,
				      struct bch_inode_info *inode,
				      struct quota_res *res,
				      unsigned sectors,
				      bool check_enospc)
{
	return 0;
}

#endif

/* i_size updates: */

struct inode_new_size {
	loff_t		new_size;
	u64		now;
	unsigned	fields;
};

static int inode_set_size(struct bch_inode_info *inode,
			  struct bch_inode_unpacked *bi,
			  void *p)
{
	struct inode_new_size *s = p;

	bi->bi_size = s->new_size;
	if (s->fields & ATTR_ATIME)
		bi->bi_atime = s->now;
	if (s->fields & ATTR_MTIME)
		bi->bi_mtime = s->now;
	if (s->fields & ATTR_CTIME)
		bi->bi_ctime = s->now;

	return 0;
}

int __must_check bch2_write_inode_size(struct bch_fs *c,
				       struct bch_inode_info *inode,
				       loff_t new_size, unsigned fields)
{
	struct inode_new_size s = {
		.new_size	= new_size,
		.now		= bch2_current_time(c),
		.fields		= fields,
	};

	return bch2_write_inode(c, inode, inode_set_size, &s, fields);
}

static void i_sectors_acct(struct bch_fs *c, struct bch_inode_info *inode,
			   struct quota_res *quota_res, s64 sectors)
{
	if (!sectors)
		return;

	mutex_lock(&inode->ei_quota_lock);
	bch2_fs_inconsistent_on((s64) inode->v.i_blocks + sectors < 0, c,
				"inode %lu i_blocks underflow: %llu + %lli < 0 (ondisk %lli)",
				inode->v.i_ino, (u64) inode->v.i_blocks, sectors,
				inode->ei_inode.bi_sectors);
	inode->v.i_blocks += sectors;

#ifdef CONFIG_BCACHEFS_QUOTA
	if (quota_res && sectors > 0) {
		BUG_ON(sectors > quota_res->sectors);
		BUG_ON(sectors > inode->ei_quota_reserved);

		quota_res->sectors -= sectors;
		inode->ei_quota_reserved -= sectors;
	} else {
		bch2_quota_acct(c, inode->ei_qid, Q_SPC, sectors, KEY_TYPE_QUOTA_WARN);
	}
#endif
	mutex_unlock(&inode->ei_quota_lock);
}

/* page state: */

/* stored in page->private: */

struct bch_page_sector {
	/* Uncompressed, fully allocated replicas (or on disk reservation): */
	unsigned		nr_replicas:4;

	/* Owns PAGE_SECTORS * replicas_reserved sized in memory reservation: */
	unsigned		replicas_reserved:4;

	/* i_sectors: */
	enum {
		SECTOR_UNALLOCATED,
		SECTOR_RESERVED,
		SECTOR_DIRTY,
		SECTOR_DIRTY_RESERVED,
		SECTOR_ALLOCATED,
	}			state:8;
};

struct bch_page_state {
	spinlock_t		lock;
	atomic_t		write_count;
	bool			uptodate;
	struct bch_page_sector	s[PAGE_SECTORS];
};

static inline struct bch_page_state *__bch2_page_state(struct page *page)
{
	return page_has_private(page)
		? (struct bch_page_state *) page_private(page)
		: NULL;
}

static inline struct bch_page_state *bch2_page_state(struct page *page)
{
	EBUG_ON(!PageLocked(page));

	return __bch2_page_state(page);
}

/* for newly allocated pages: */
static void __bch2_page_state_release(struct page *page)
{
	kfree(detach_page_private(page));
}

static void bch2_page_state_release(struct page *page)
{
	EBUG_ON(!PageLocked(page));
	__bch2_page_state_release(page);
}

/* for newly allocated pages: */
static struct bch_page_state *__bch2_page_state_create(struct page *page,
						       gfp_t gfp)
{
	struct bch_page_state *s;

	s = kzalloc(sizeof(*s), GFP_NOFS|gfp);
	if (!s)
		return NULL;

	spin_lock_init(&s->lock);
	attach_page_private(page, s);
	return s;
}

static struct bch_page_state *bch2_page_state_create(struct page *page,
						     gfp_t gfp)
{
	return bch2_page_state(page) ?: __bch2_page_state_create(page, gfp);
}

static unsigned bkey_to_sector_state(const struct bkey *k)
{
	if (k->type == KEY_TYPE_reservation)
		return SECTOR_RESERVED;
	if (bkey_extent_is_allocation(k))
		return SECTOR_ALLOCATED;
	return SECTOR_UNALLOCATED;
}

static void __bch2_page_state_set(struct page *page,
				  unsigned pg_offset, unsigned pg_len,
				  unsigned nr_ptrs, unsigned state)
{
	struct bch_page_state *s = bch2_page_state_create(page, __GFP_NOFAIL);
	unsigned i;

	BUG_ON(pg_offset >= PAGE_SECTORS);
	BUG_ON(pg_offset + pg_len > PAGE_SECTORS);

	spin_lock(&s->lock);

	for (i = pg_offset; i < pg_offset + pg_len; i++) {
		s->s[i].nr_replicas = nr_ptrs;
		s->s[i].state = state;
	}

	if (i == PAGE_SECTORS)
		s->uptodate = true;

	spin_unlock(&s->lock);
}

static int bch2_page_state_set(struct bch_fs *c, subvol_inum inum,
			       struct page **pages, unsigned nr_pages)
{
	struct btree_trans trans;
	struct btree_iter iter;
	struct bkey_s_c k;
	u64 offset = pages[0]->index << PAGE_SECTORS_SHIFT;
	unsigned pg_idx = 0;
	u32 snapshot;
	int ret;

	bch2_trans_init(&trans, c, 0, 0);
retry:
	bch2_trans_begin(&trans);

	ret = bch2_subvolume_get_snapshot(&trans, inum.subvol, &snapshot);
	if (ret)
		goto err;

	for_each_btree_key_norestart(&trans, iter, BTREE_ID_extents,
			   SPOS(inum.inum, offset, snapshot),
			   BTREE_ITER_SLOTS, k, ret) {
		unsigned nr_ptrs = bch2_bkey_nr_ptrs_fully_allocated(k);
		unsigned state = bkey_to_sector_state(k.k);

		while (pg_idx < nr_pages) {
			struct page *page = pages[pg_idx];
			u64 pg_start = page->index << PAGE_SECTORS_SHIFT;
			u64 pg_end = (page->index + 1) << PAGE_SECTORS_SHIFT;
			unsigned pg_offset = max(bkey_start_offset(k.k), pg_start) - pg_start;
			unsigned pg_len = min(k.k->p.offset, pg_end) - pg_offset - pg_start;

			BUG_ON(k.k->p.offset < pg_start);
			BUG_ON(bkey_start_offset(k.k) > pg_end);

			if (!bch2_page_state_create(page, __GFP_NOFAIL)->uptodate)
				__bch2_page_state_set(page, pg_offset, pg_len, nr_ptrs, state);

			if (k.k->p.offset < pg_end)
				break;
			pg_idx++;
		}

		if (pg_idx == nr_pages)
			break;
	}

	offset = iter.pos.offset;
	bch2_trans_iter_exit(&trans, &iter);
err:
	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
		goto retry;
	bch2_trans_exit(&trans);

	return ret;
}

static void bch2_bio_page_state_set(struct bio *bio, struct bkey_s_c k)
{
	struct bvec_iter iter;
	struct bio_vec bv;
	unsigned nr_ptrs = k.k->type == KEY_TYPE_reflink_v
		? 0 : bch2_bkey_nr_ptrs_fully_allocated(k);
	unsigned state = bkey_to_sector_state(k.k);

	bio_for_each_segment(bv, bio, iter)
		__bch2_page_state_set(bv.bv_page, bv.bv_offset >> 9,
				      bv.bv_len >> 9, nr_ptrs, state);
}

static void mark_pagecache_unallocated(struct bch_inode_info *inode,
				       u64 start, u64 end)
{
	pgoff_t index = start >> PAGE_SECTORS_SHIFT;
	pgoff_t end_index = (end - 1) >> PAGE_SECTORS_SHIFT;
	struct folio_batch fbatch;
	unsigned i, j;

	if (end <= start)
		return;

	folio_batch_init(&fbatch);

	while (filemap_get_folios(inode->v.i_mapping,
				  &index, end_index, &fbatch)) {
		for (i = 0; i < folio_batch_count(&fbatch); i++) {
			struct folio *folio = fbatch.folios[i];
			u64 pg_start = folio->index << PAGE_SECTORS_SHIFT;
			u64 pg_end = (folio->index + 1) << PAGE_SECTORS_SHIFT;
			unsigned pg_offset = max(start, pg_start) - pg_start;
			unsigned pg_len = min(end, pg_end) - pg_offset - pg_start;
			struct bch_page_state *s;

			BUG_ON(end <= pg_start);
			BUG_ON(pg_offset >= PAGE_SECTORS);
			BUG_ON(pg_offset + pg_len > PAGE_SECTORS);

			folio_lock(folio);
			s = bch2_page_state(&folio->page);

			if (s) {
				spin_lock(&s->lock);
				for (j = pg_offset; j < pg_offset + pg_len; j++)
					s->s[j].nr_replicas = 0;
				spin_unlock(&s->lock);
			}

			folio_unlock(folio);
		}
		folio_batch_release(&fbatch);
		cond_resched();
	}
}

static void mark_pagecache_reserved(struct bch_inode_info *inode,
				    u64 start, u64 end)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	pgoff_t index = start >> PAGE_SECTORS_SHIFT;
	pgoff_t end_index = (end - 1) >> PAGE_SECTORS_SHIFT;
	struct folio_batch fbatch;
	s64 i_sectors_delta = 0;
	unsigned i, j;

	if (end <= start)
		return;

	folio_batch_init(&fbatch);

	while (filemap_get_folios(inode->v.i_mapping,
				  &index, end_index, &fbatch)) {
		for (i = 0; i < folio_batch_count(&fbatch); i++) {
			struct folio *folio = fbatch.folios[i];
			u64 pg_start = folio->index << PAGE_SECTORS_SHIFT;
			u64 pg_end = (folio->index + 1) << PAGE_SECTORS_SHIFT;
			unsigned pg_offset = max(start, pg_start) - pg_start;
			unsigned pg_len = min(end, pg_end) - pg_offset - pg_start;
			struct bch_page_state *s;

			BUG_ON(end <= pg_start);
			BUG_ON(pg_offset >= PAGE_SECTORS);
			BUG_ON(pg_offset + pg_len > PAGE_SECTORS);

			folio_lock(folio);
			s = bch2_page_state(&folio->page);

			if (s) {
				spin_lock(&s->lock);
				for (j = pg_offset; j < pg_offset + pg_len; j++)
					switch (s->s[j].state) {
					case SECTOR_UNALLOCATED:
						s->s[j].state = SECTOR_RESERVED;
						break;
					case SECTOR_DIRTY:
						s->s[j].state = SECTOR_DIRTY_RESERVED;
						i_sectors_delta--;
						break;
					default:
						break;
					}
				spin_unlock(&s->lock);
			}

			folio_unlock(folio);
		}
		folio_batch_release(&fbatch);
		cond_resched();
	}

	i_sectors_acct(c, inode, NULL, i_sectors_delta);
}

static inline unsigned inode_nr_replicas(struct bch_fs *c, struct bch_inode_info *inode)
{
	/* XXX: this should not be open coded */
	return inode->ei_inode.bi_data_replicas
		? inode->ei_inode.bi_data_replicas - 1
		: c->opts.data_replicas;
}

static inline unsigned sectors_to_reserve(struct bch_page_sector *s,
						  unsigned nr_replicas)
{
	return max(0, (int) nr_replicas -
		   s->nr_replicas -
		   s->replicas_reserved);
}

static int bch2_get_page_disk_reservation(struct bch_fs *c,
				struct bch_inode_info *inode,
				struct page *page, bool check_enospc)
{
	struct bch_page_state *s = bch2_page_state_create(page, 0);
	unsigned nr_replicas = inode_nr_replicas(c, inode);
	struct disk_reservation disk_res = { 0 };
	unsigned i, disk_res_sectors = 0;
	int ret;

	if (!s)
		return -ENOMEM;

	for (i = 0; i < ARRAY_SIZE(s->s); i++)
		disk_res_sectors += sectors_to_reserve(&s->s[i], nr_replicas);

	if (!disk_res_sectors)
		return 0;

	ret = bch2_disk_reservation_get(c, &disk_res,
					disk_res_sectors, 1,
					!check_enospc
					? BCH_DISK_RESERVATION_NOFAIL
					: 0);
	if (unlikely(ret))
		return ret;

	for (i = 0; i < ARRAY_SIZE(s->s); i++)
		s->s[i].replicas_reserved +=
			sectors_to_reserve(&s->s[i], nr_replicas);

	return 0;
}

struct bch2_page_reservation {
	struct disk_reservation	disk;
	struct quota_res	quota;
};

static void bch2_page_reservation_init(struct bch_fs *c,
			struct bch_inode_info *inode,
			struct bch2_page_reservation *res)
{
	memset(res, 0, sizeof(*res));

	res->disk.nr_replicas = inode_nr_replicas(c, inode);
}

static void bch2_page_reservation_put(struct bch_fs *c,
			struct bch_inode_info *inode,
			struct bch2_page_reservation *res)
{
	bch2_disk_reservation_put(c, &res->disk);
	bch2_quota_reservation_put(c, inode, &res->quota);
}

static int bch2_page_reservation_get(struct bch_fs *c,
			struct bch_inode_info *inode, struct page *page,
			struct bch2_page_reservation *res,
			unsigned offset, unsigned len)
{
	struct bch_page_state *s = bch2_page_state_create(page, 0);
	unsigned i, disk_sectors = 0, quota_sectors = 0;
	int ret;

	if (!s)
		return -ENOMEM;

	BUG_ON(!s->uptodate);

	for (i = round_down(offset, block_bytes(c)) >> 9;
	     i < round_up(offset + len, block_bytes(c)) >> 9;
	     i++) {
		disk_sectors += sectors_to_reserve(&s->s[i],
						res->disk.nr_replicas);
		quota_sectors += s->s[i].state == SECTOR_UNALLOCATED;
	}

	if (disk_sectors) {
		ret = bch2_disk_reservation_add(c, &res->disk, disk_sectors, 0);
		if (unlikely(ret))
			return ret;
	}

	if (quota_sectors) {
		ret = bch2_quota_reservation_add(c, inode, &res->quota,
						 quota_sectors, true);
		if (unlikely(ret)) {
			struct disk_reservation tmp = {
				.sectors = disk_sectors
			};

			bch2_disk_reservation_put(c, &tmp);
			res->disk.sectors -= disk_sectors;
			return ret;
		}
	}

	return 0;
}

static void bch2_clear_page_bits(struct page *page)
{
	struct bch_inode_info *inode = to_bch_ei(page->mapping->host);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch_page_state *s = bch2_page_state(page);
	struct disk_reservation disk_res = { 0 };
	int i, dirty_sectors = 0;

	if (!s)
		return;

	EBUG_ON(!PageLocked(page));
	EBUG_ON(PageWriteback(page));

	for (i = 0; i < ARRAY_SIZE(s->s); i++) {
		disk_res.sectors += s->s[i].replicas_reserved;
		s->s[i].replicas_reserved = 0;

		switch (s->s[i].state) {
		case SECTOR_DIRTY:
			s->s[i].state = SECTOR_UNALLOCATED;
			--dirty_sectors;
			break;
		case SECTOR_DIRTY_RESERVED:
			s->s[i].state = SECTOR_RESERVED;
			break;
		default:
			break;
		}
	}

	bch2_disk_reservation_put(c, &disk_res);

	i_sectors_acct(c, inode, NULL, dirty_sectors);

	bch2_page_state_release(page);
}

static void bch2_set_page_dirty(struct bch_fs *c,
			struct bch_inode_info *inode, struct page *page,
			struct bch2_page_reservation *res,
			unsigned offset, unsigned len)
{
	struct bch_page_state *s = bch2_page_state(page);
	unsigned i, dirty_sectors = 0;

	WARN_ON((u64) page_offset(page) + offset + len >
		round_up((u64) i_size_read(&inode->v), block_bytes(c)));

	spin_lock(&s->lock);

	for (i = round_down(offset, block_bytes(c)) >> 9;
	     i < round_up(offset + len, block_bytes(c)) >> 9;
	     i++) {
		unsigned sectors = sectors_to_reserve(&s->s[i],
						res->disk.nr_replicas);

		/*
		 * This can happen if we race with the error path in
		 * bch2_writepage_io_done():
		 */
		sectors = min_t(unsigned, sectors, res->disk.sectors);

		s->s[i].replicas_reserved += sectors;
		res->disk.sectors -= sectors;

		switch (s->s[i].state) {
		case SECTOR_UNALLOCATED:
			s->s[i].state = SECTOR_DIRTY;
			dirty_sectors++;
			break;
		case SECTOR_RESERVED:
			s->s[i].state = SECTOR_DIRTY_RESERVED;
			break;
		default:
			break;
		}
	}

	spin_unlock(&s->lock);

	i_sectors_acct(c, inode, &res->quota, dirty_sectors);

	if (!PageDirty(page))
		__set_page_dirty_nobuffers(page);
}

vm_fault_t bch2_page_fault(struct vm_fault *vmf)
{
	struct file *file = vmf->vma->vm_file;
	struct address_space *mapping = file->f_mapping;
	struct address_space *fdm = faults_disabled_mapping();
	struct bch_inode_info *inode = file_bch_inode(file);
	int ret;

	if (fdm == mapping)
		return VM_FAULT_SIGBUS;

	/* Lock ordering: */
	if (fdm > mapping) {
		struct bch_inode_info *fdm_host = to_bch_ei(fdm->host);

		if (bch2_pagecache_add_tryget(&inode->ei_pagecache_lock))
			goto got_lock;

		bch2_pagecache_block_put(&fdm_host->ei_pagecache_lock);

		bch2_pagecache_add_get(&inode->ei_pagecache_lock);
		bch2_pagecache_add_put(&inode->ei_pagecache_lock);

		bch2_pagecache_block_get(&fdm_host->ei_pagecache_lock);

		/* Signal that lock has been dropped: */
		set_fdm_dropped_locks();
		return VM_FAULT_SIGBUS;
	}

	bch2_pagecache_add_get(&inode->ei_pagecache_lock);
got_lock:
	ret = filemap_fault(vmf);
	bch2_pagecache_add_put(&inode->ei_pagecache_lock);

	return ret;
}

vm_fault_t bch2_page_mkwrite(struct vm_fault *vmf)
{
	struct page *page = vmf->page;
	struct file *file = vmf->vma->vm_file;
	struct bch_inode_info *inode = file_bch_inode(file);
	struct address_space *mapping = file->f_mapping;
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch2_page_reservation res;
	unsigned len;
	loff_t isize;
	int ret;

	bch2_page_reservation_init(c, inode, &res);

	sb_start_pagefault(inode->v.i_sb);
	file_update_time(file);

	/*
	 * Not strictly necessary, but helps avoid dio writes livelocking in
	 * write_invalidate_inode_pages_range() - can drop this if/when we get
	 * a write_invalidate_inode_pages_range() that works without dropping
	 * page lock before invalidating page
	 */
	bch2_pagecache_add_get(&inode->ei_pagecache_lock);

	lock_page(page);
	isize = i_size_read(&inode->v);

	if (page->mapping != mapping || page_offset(page) >= isize) {
		unlock_page(page);
		ret = VM_FAULT_NOPAGE;
		goto out;
	}

	len = min_t(loff_t, PAGE_SIZE, isize - page_offset(page));

	if (!bch2_page_state_create(page, __GFP_NOFAIL)->uptodate) {
		if (bch2_page_state_set(c, inode_inum(inode), &page, 1)) {
			unlock_page(page);
			ret = VM_FAULT_SIGBUS;
			goto out;
		}
	}

	if (bch2_page_reservation_get(c, inode, page, &res, 0, len)) {
		unlock_page(page);
		ret = VM_FAULT_SIGBUS;
		goto out;
	}

	bch2_set_page_dirty(c, inode, page, &res, 0, len);
	bch2_page_reservation_put(c, inode, &res);

	wait_for_stable_page(page);
	ret = VM_FAULT_LOCKED;
out:
	bch2_pagecache_add_put(&inode->ei_pagecache_lock);
	sb_end_pagefault(inode->v.i_sb);

	return ret;
}

void bch2_invalidate_folio(struct folio *folio, size_t offset, size_t length)
{
	if (offset || length < folio_size(folio))
		return;

	bch2_clear_page_bits(&folio->page);
}

bool bch2_release_folio(struct folio *folio, gfp_t gfp_mask)
{
	if (folio_test_dirty(folio) || folio_test_writeback(folio))
		return false;

	bch2_clear_page_bits(&folio->page);
	return true;
}

/* readpage(s): */

static void bch2_readpages_end_io(struct bio *bio)
{
	struct bvec_iter_all iter;
	struct bio_vec *bv;

	bio_for_each_segment_all(bv, bio, iter) {
		struct page *page = bv->bv_page;

		if (!bio->bi_status) {
			SetPageUptodate(page);
		} else {
			ClearPageUptodate(page);
			SetPageError(page);
		}
		unlock_page(page);
	}

	bio_put(bio);
}

struct readpages_iter {
	struct address_space	*mapping;
	struct page		**pages;
	unsigned		nr_pages;
	unsigned		idx;
	pgoff_t			offset;
};

static int readpages_iter_init(struct readpages_iter *iter,
			       struct readahead_control *ractl)
{
	unsigned i, nr_pages = readahead_count(ractl);

	memset(iter, 0, sizeof(*iter));

	iter->mapping	= ractl->mapping;
	iter->offset	= readahead_index(ractl);
	iter->nr_pages	= nr_pages;

	iter->pages = kmalloc_array(nr_pages, sizeof(struct page *), GFP_NOFS);
	if (!iter->pages)
		return -ENOMEM;

	nr_pages = __readahead_batch(ractl, iter->pages, nr_pages);
	for (i = 0; i < nr_pages; i++) {
		__bch2_page_state_create(iter->pages[i], __GFP_NOFAIL);
		put_page(iter->pages[i]);
	}

	return 0;
}

static inline struct page *readpage_iter_next(struct readpages_iter *iter)
{
	if (iter->idx >= iter->nr_pages)
		return NULL;

	EBUG_ON(iter->pages[iter->idx]->index != iter->offset + iter->idx);

	return iter->pages[iter->idx];
}

static bool extent_partial_reads_expensive(struct bkey_s_c k)
{
	struct bkey_ptrs_c ptrs = bch2_bkey_ptrs_c(k);
	struct bch_extent_crc_unpacked crc;
	const union bch_extent_entry *i;

	bkey_for_each_crc(k.k, ptrs, crc, i)
		if (crc.csum_type || crc.compression_type)
			return true;
	return false;
}

static void readpage_bio_extend(struct readpages_iter *iter,
				struct bio *bio,
				unsigned sectors_this_extent,
				bool get_more)
{
	while (bio_sectors(bio) < sectors_this_extent &&
	       bio->bi_vcnt < bio->bi_max_vecs) {
		pgoff_t page_offset = bio_end_sector(bio) >> PAGE_SECTORS_SHIFT;
		struct page *page = readpage_iter_next(iter);
		int ret;

		if (page) {
			if (iter->offset + iter->idx != page_offset)
				break;

			iter->idx++;
		} else {
			if (!get_more)
				break;

			page = xa_load(&iter->mapping->i_pages, page_offset);
			if (page && !xa_is_value(page))
				break;

			page = __page_cache_alloc(readahead_gfp_mask(iter->mapping));
			if (!page)
				break;

			if (!__bch2_page_state_create(page, 0)) {
				put_page(page);
				break;
			}

			ret = add_to_page_cache_lru(page, iter->mapping,
						    page_offset, GFP_NOFS);
			if (ret) {
				__bch2_page_state_release(page);
				put_page(page);
				break;
			}

			put_page(page);
		}

		BUG_ON(!bio_add_page(bio, page, PAGE_SIZE, 0));
	}
}

static void bchfs_read(struct btree_trans *trans,
		       struct bch_read_bio *rbio,
		       subvol_inum inum,
		       struct readpages_iter *readpages_iter)
{
	struct bch_fs *c = trans->c;
	struct btree_iter iter;
	struct bkey_buf sk;
	int flags = BCH_READ_RETRY_IF_STALE|
		BCH_READ_MAY_PROMOTE;
	u32 snapshot;
	int ret = 0;

	rbio->c = c;
	rbio->start_time = local_clock();
	rbio->subvol = inum.subvol;

	bch2_bkey_buf_init(&sk);
retry:
	bch2_trans_begin(trans);
	iter = (struct btree_iter) { NULL };

	ret = bch2_subvolume_get_snapshot(trans, inum.subvol, &snapshot);
	if (ret)
		goto err;

	bch2_trans_iter_init(trans, &iter, BTREE_ID_extents,
			     SPOS(inum.inum, rbio->bio.bi_iter.bi_sector, snapshot),
			     BTREE_ITER_SLOTS);
	while (1) {
		struct bkey_s_c k;
		unsigned bytes, sectors, offset_into_extent;
		enum btree_id data_btree = BTREE_ID_extents;

		/*
		 * read_extent -> io_time_reset may cause a transaction restart
		 * without returning an error, we need to check for that here:
		 */
		ret = bch2_trans_relock(trans);
		if (ret)
			break;

		bch2_btree_iter_set_pos(&iter,
				POS(inum.inum, rbio->bio.bi_iter.bi_sector));

		k = bch2_btree_iter_peek_slot(&iter);
		ret = bkey_err(k);
		if (ret)
			break;

		offset_into_extent = iter.pos.offset -
			bkey_start_offset(k.k);
		sectors = k.k->size - offset_into_extent;

		bch2_bkey_buf_reassemble(&sk, c, k);

		ret = bch2_read_indirect_extent(trans, &data_btree,
					&offset_into_extent, &sk);
		if (ret)
			break;

		k = bkey_i_to_s_c(sk.k);

		sectors = min(sectors, k.k->size - offset_into_extent);

		if (readpages_iter)
			readpage_bio_extend(readpages_iter, &rbio->bio, sectors,
					    extent_partial_reads_expensive(k));

		bytes = min(sectors, bio_sectors(&rbio->bio)) << 9;
		swap(rbio->bio.bi_iter.bi_size, bytes);

		if (rbio->bio.bi_iter.bi_size == bytes)
			flags |= BCH_READ_LAST_FRAGMENT;

		bch2_bio_page_state_set(&rbio->bio, k);

		bch2_read_extent(trans, rbio, iter.pos,
				 data_btree, k, offset_into_extent, flags);

		if (flags & BCH_READ_LAST_FRAGMENT)
			break;

		swap(rbio->bio.bi_iter.bi_size, bytes);
		bio_advance(&rbio->bio, bytes);

		ret = btree_trans_too_many_iters(trans);
		if (ret)
			break;
	}
err:
	bch2_trans_iter_exit(trans, &iter);

	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
		goto retry;

	if (ret) {
		bch_err_inum_ratelimited(c, inum.inum,
				"read error %i from btree lookup", ret);
		rbio->bio.bi_status = BLK_STS_IOERR;
		bio_endio(&rbio->bio);
	}

	bch2_bkey_buf_exit(&sk, c);
}

void bch2_readahead(struct readahead_control *ractl)
{
	struct bch_inode_info *inode = to_bch_ei(ractl->mapping->host);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch_io_opts opts = io_opts(c, &inode->ei_inode);
	struct btree_trans trans;
	struct page *page;
	struct readpages_iter readpages_iter;
	int ret;

	ret = readpages_iter_init(&readpages_iter, ractl);
	BUG_ON(ret);

	bch2_trans_init(&trans, c, 0, 0);

	bch2_pagecache_add_get(&inode->ei_pagecache_lock);

	while ((page = readpage_iter_next(&readpages_iter))) {
		pgoff_t index = readpages_iter.offset + readpages_iter.idx;
		unsigned n = min_t(unsigned,
				   readpages_iter.nr_pages -
				   readpages_iter.idx,
				   BIO_MAX_VECS);
		struct bch_read_bio *rbio =
			rbio_init(bio_alloc_bioset(NULL, n, REQ_OP_READ,
						   GFP_NOFS, &c->bio_read),
				  opts);

		readpages_iter.idx++;

		rbio->bio.bi_iter.bi_sector = (sector_t) index << PAGE_SECTORS_SHIFT;
		rbio->bio.bi_end_io = bch2_readpages_end_io;
		BUG_ON(!bio_add_page(&rbio->bio, page, PAGE_SIZE, 0));

		bchfs_read(&trans, rbio, inode_inum(inode),
			   &readpages_iter);
	}

	bch2_pagecache_add_put(&inode->ei_pagecache_lock);

	bch2_trans_exit(&trans);
	kfree(readpages_iter.pages);
}

static void __bchfs_readpage(struct bch_fs *c, struct bch_read_bio *rbio,
			     subvol_inum inum, struct page *page)
{
	struct btree_trans trans;

	bch2_page_state_create(page, __GFP_NOFAIL);

	bio_set_op_attrs(&rbio->bio, REQ_OP_READ, REQ_SYNC);
	rbio->bio.bi_iter.bi_sector =
		(sector_t) page->index << PAGE_SECTORS_SHIFT;
	BUG_ON(!bio_add_page(&rbio->bio, page, PAGE_SIZE, 0));

	bch2_trans_init(&trans, c, 0, 0);
	bchfs_read(&trans, rbio, inum, NULL);
	bch2_trans_exit(&trans);
}

static void bch2_read_single_page_end_io(struct bio *bio)
{
	complete(bio->bi_private);
}

static int bch2_read_single_page(struct page *page,
				 struct address_space *mapping)
{
	struct bch_inode_info *inode = to_bch_ei(mapping->host);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch_read_bio *rbio;
	int ret;
	DECLARE_COMPLETION_ONSTACK(done);

	rbio = rbio_init(bio_alloc_bioset(NULL, 1, REQ_OP_READ, GFP_NOFS, &c->bio_read),
			 io_opts(c, &inode->ei_inode));
	rbio->bio.bi_private = &done;
	rbio->bio.bi_end_io = bch2_read_single_page_end_io;

	__bchfs_readpage(c, rbio, inode_inum(inode), page);
	wait_for_completion(&done);

	ret = blk_status_to_errno(rbio->bio.bi_status);
	bio_put(&rbio->bio);

	if (ret < 0)
		return ret;

	SetPageUptodate(page);
	return 0;
}

int bch2_read_folio(struct file *file, struct folio *folio)
{
	struct page *page = &folio->page;
	int ret;

	ret = bch2_read_single_page(page, page->mapping);
	folio_unlock(folio);
	return bch2_err_class(ret);
}

/* writepages: */

struct bch_writepage_state {
	struct bch_writepage_io	*io;
	struct bch_io_opts	opts;
};

static inline struct bch_writepage_state bch_writepage_state_init(struct bch_fs *c,
								  struct bch_inode_info *inode)
{
	return (struct bch_writepage_state) {
		.opts = io_opts(c, &inode->ei_inode)
	};
}

static void bch2_writepage_io_free(struct closure *cl)
{
	struct bch_writepage_io *io = container_of(cl,
					struct bch_writepage_io, cl);

	bio_put(&io->op.wbio.bio);
}

static void bch2_writepage_io_done(struct closure *cl)
{
	struct bch_writepage_io *io = container_of(cl,
					struct bch_writepage_io, cl);
	struct bch_fs *c = io->op.c;
	struct bio *bio = &io->op.wbio.bio;
	struct bvec_iter_all iter;
	struct bio_vec *bvec;
	unsigned i;

	if (io->op.error) {
		set_bit(EI_INODE_ERROR, &io->inode->ei_flags);

		bio_for_each_segment_all(bvec, bio, iter) {
			struct bch_page_state *s;

			SetPageError(bvec->bv_page);
			mapping_set_error(bvec->bv_page->mapping, -EIO);

			s = __bch2_page_state(bvec->bv_page);
			spin_lock(&s->lock);
			for (i = 0; i < PAGE_SECTORS; i++)
				s->s[i].nr_replicas = 0;
			spin_unlock(&s->lock);
		}
	}

	if (io->op.flags & BCH_WRITE_WROTE_DATA_INLINE) {
		bio_for_each_segment_all(bvec, bio, iter) {
			struct bch_page_state *s;

			s = __bch2_page_state(bvec->bv_page);
			spin_lock(&s->lock);
			for (i = 0; i < PAGE_SECTORS; i++)
				s->s[i].nr_replicas = 0;
			spin_unlock(&s->lock);
		}
	}

	/*
	 * racing with fallocate can cause us to add fewer sectors than
	 * expected - but we shouldn't add more sectors than expected:
	 */
	WARN_ON_ONCE(io->op.i_sectors_delta > 0);

	/*
	 * (error (due to going RO) halfway through a page can screw that up
	 * slightly)
	 * XXX wtf?
	   BUG_ON(io->op.op.i_sectors_delta >= PAGE_SECTORS);
	 */

	/*
	 * PageWriteback is effectively our ref on the inode - fixup i_blocks
	 * before calling end_page_writeback:
	 */
	i_sectors_acct(c, io->inode, NULL, io->op.i_sectors_delta);

	bio_for_each_segment_all(bvec, bio, iter) {
		struct bch_page_state *s = __bch2_page_state(bvec->bv_page);

		if (atomic_dec_and_test(&s->write_count))
			end_page_writeback(bvec->bv_page);
	}

	closure_return_with_destructor(&io->cl, bch2_writepage_io_free);
}

static void bch2_writepage_do_io(struct bch_writepage_state *w)
{
	struct bch_writepage_io *io = w->io;

	w->io = NULL;
	closure_call(&io->op.cl, bch2_write, NULL, &io->cl);
	continue_at(&io->cl, bch2_writepage_io_done, NULL);
}

/*
 * Get a bch_writepage_io and add @page to it - appending to an existing one if
 * possible, else allocating a new one:
 */
static void bch2_writepage_io_alloc(struct bch_fs *c,
				    struct writeback_control *wbc,
				    struct bch_writepage_state *w,
				    struct bch_inode_info *inode,
				    u64 sector,
				    unsigned nr_replicas)
{
	struct bch_write_op *op;

	w->io = container_of(bio_alloc_bioset(NULL, BIO_MAX_VECS,
					      REQ_OP_WRITE,
					      GFP_NOFS,
					      &c->writepage_bioset),
			     struct bch_writepage_io, op.wbio.bio);

	closure_init(&w->io->cl, NULL);
	w->io->inode		= inode;

	op			= &w->io->op;
	bch2_write_op_init(op, c, w->opts);
	op->target		= w->opts.foreground_target;
	op->nr_replicas		= nr_replicas;
	op->res.nr_replicas	= nr_replicas;
	op->write_point		= writepoint_hashed(inode->ei_last_dirtied);
	op->subvol		= inode->ei_subvol;
	op->pos			= POS(inode->v.i_ino, sector);
	op->wbio.bio.bi_iter.bi_sector = sector;
	op->wbio.bio.bi_opf	= wbc_to_write_flags(wbc);
}

static int __bch2_writepage(struct page *page,
			    struct writeback_control *wbc,
			    void *data)
{
	struct bch_inode_info *inode = to_bch_ei(page->mapping->host);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch_writepage_state *w = data;
	struct bch_page_state *s, orig;
	unsigned i, offset, nr_replicas_this_write = U32_MAX;
	loff_t i_size = i_size_read(&inode->v);
	pgoff_t end_index = i_size >> PAGE_SHIFT;
	int ret;

	EBUG_ON(!PageUptodate(page));

	/* Is the page fully inside i_size? */
	if (page->index < end_index)
		goto do_io;

	/* Is the page fully outside i_size? (truncate in progress) */
	offset = i_size & (PAGE_SIZE - 1);
	if (page->index > end_index || !offset) {
		unlock_page(page);
		return 0;
	}

	/*
	 * The page straddles i_size.  It must be zeroed out on each and every
	 * writepage invocation because it may be mmapped.  "A file is mapped
	 * in multiples of the page size.  For a file that is not a multiple of
	 * the  page size, the remaining memory is zeroed when mapped, and
	 * writes to that region are not written out to the file."
	 */
	zero_user_segment(page, offset, PAGE_SIZE);
do_io:
	s = bch2_page_state_create(page, __GFP_NOFAIL);

	/*
	 * Things get really hairy with errors during writeback:
	 */
	ret = bch2_get_page_disk_reservation(c, inode, page, false);
	BUG_ON(ret);

	/* Before unlocking the page, get copy of reservations: */
	spin_lock(&s->lock);
	orig = *s;
	spin_unlock(&s->lock);

	for (i = 0; i < PAGE_SECTORS; i++) {
		if (s->s[i].state < SECTOR_DIRTY)
			continue;

		nr_replicas_this_write =
			min_t(unsigned, nr_replicas_this_write,
			      s->s[i].nr_replicas +
			      s->s[i].replicas_reserved);
	}

	for (i = 0; i < PAGE_SECTORS; i++) {
		if (s->s[i].state < SECTOR_DIRTY)
			continue;

		s->s[i].nr_replicas = w->opts.compression
			? 0 : nr_replicas_this_write;

		s->s[i].replicas_reserved = 0;
		s->s[i].state = SECTOR_ALLOCATED;
	}

	BUG_ON(atomic_read(&s->write_count));
	atomic_set(&s->write_count, 1);

	BUG_ON(PageWriteback(page));
	set_page_writeback(page);

	unlock_page(page);

	offset = 0;
	while (1) {
		unsigned sectors = 0, dirty_sectors = 0, reserved_sectors = 0;
		u64 sector;

		while (offset < PAGE_SECTORS &&
		       orig.s[offset].state < SECTOR_DIRTY)
			offset++;

		if (offset == PAGE_SECTORS)
			break;

		while (offset + sectors < PAGE_SECTORS &&
		       orig.s[offset + sectors].state >= SECTOR_DIRTY) {
			reserved_sectors += orig.s[offset + sectors].replicas_reserved;
			dirty_sectors += orig.s[offset + sectors].state == SECTOR_DIRTY;
			sectors++;
		}
		BUG_ON(!sectors);

		sector = ((u64) page->index << PAGE_SECTORS_SHIFT) + offset;

		if (w->io &&
		    (w->io->op.res.nr_replicas != nr_replicas_this_write ||
		     bio_full(&w->io->op.wbio.bio, PAGE_SIZE) ||
		     w->io->op.wbio.bio.bi_iter.bi_size + (sectors << 9) >=
		     (BIO_MAX_VECS * PAGE_SIZE) ||
		     bio_end_sector(&w->io->op.wbio.bio) != sector))
			bch2_writepage_do_io(w);

		if (!w->io)
			bch2_writepage_io_alloc(c, wbc, w, inode, sector,
						nr_replicas_this_write);

		atomic_inc(&s->write_count);

		BUG_ON(inode != w->io->inode);
		BUG_ON(!bio_add_page(&w->io->op.wbio.bio, page,
				     sectors << 9, offset << 9));

		/* Check for writing past i_size: */
		WARN_ON_ONCE((bio_end_sector(&w->io->op.wbio.bio) << 9) >
			     round_up(i_size, block_bytes(c)));

		w->io->op.res.sectors += reserved_sectors;
		w->io->op.i_sectors_delta -= dirty_sectors;
		w->io->op.new_i_size = i_size;

		offset += sectors;
	}

	if (atomic_dec_and_test(&s->write_count))
		end_page_writeback(page);

	return 0;
}

int bch2_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
	struct bch_fs *c = mapping->host->i_sb->s_fs_info;
	struct bch_writepage_state w =
		bch_writepage_state_init(c, to_bch_ei(mapping->host));
	struct blk_plug plug;
	int ret;

	blk_start_plug(&plug);
	ret = write_cache_pages(mapping, wbc, __bch2_writepage, &w);
	if (w.io)
		bch2_writepage_do_io(&w);
	blk_finish_plug(&plug);
	return bch2_err_class(ret);
}

/* buffered writes: */

int bch2_write_begin(struct file *file, struct address_space *mapping,
		     loff_t pos, unsigned len,
		     struct page **pagep, void **fsdata)
{
	struct bch_inode_info *inode = to_bch_ei(mapping->host);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch2_page_reservation *res;
	pgoff_t index = pos >> PAGE_SHIFT;
	unsigned offset = pos & (PAGE_SIZE - 1);
	struct page *page;
	int ret = -ENOMEM;

	res = kmalloc(sizeof(*res), GFP_KERNEL);
	if (!res)
		return -ENOMEM;

	bch2_page_reservation_init(c, inode, res);
	*fsdata = res;

	bch2_pagecache_add_get(&inode->ei_pagecache_lock);

	page = grab_cache_page_write_begin(mapping, index);
	if (!page)
		goto err_unlock;

	if (PageUptodate(page))
		goto out;

	/* If we're writing entire page, don't need to read it in first: */
	if (len == PAGE_SIZE)
		goto out;

	if (!offset && pos + len >= inode->v.i_size) {
		zero_user_segment(page, len, PAGE_SIZE);
		flush_dcache_page(page);
		goto out;
	}

	if (index > inode->v.i_size >> PAGE_SHIFT) {
		zero_user_segments(page, 0, offset, offset + len, PAGE_SIZE);
		flush_dcache_page(page);
		goto out;
	}
readpage:
	ret = bch2_read_single_page(page, mapping);
	if (ret)
		goto err;
out:
	if (!bch2_page_state_create(page, __GFP_NOFAIL)->uptodate) {
		ret = bch2_page_state_set(c, inode_inum(inode), &page, 1);
		if (ret)
			goto err;
	}

	ret = bch2_page_reservation_get(c, inode, page, res, offset, len);
	if (ret) {
		if (!PageUptodate(page)) {
			/*
			 * If the page hasn't been read in, we won't know if we
			 * actually need a reservation - we don't actually need
			 * to read here, we just need to check if the page is
			 * fully backed by uncompressed data:
			 */
			goto readpage;
		}

		goto err;
	}

	*pagep = page;
	return 0;
err:
	unlock_page(page);
	put_page(page);
	*pagep = NULL;
err_unlock:
	bch2_pagecache_add_put(&inode->ei_pagecache_lock);
	kfree(res);
	*fsdata = NULL;
	return bch2_err_class(ret);
}

int bch2_write_end(struct file *file, struct address_space *mapping,
		   loff_t pos, unsigned len, unsigned copied,
		   struct page *page, void *fsdata)
{
	struct bch_inode_info *inode = to_bch_ei(mapping->host);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch2_page_reservation *res = fsdata;
	unsigned offset = pos & (PAGE_SIZE - 1);

	lockdep_assert_held(&inode->v.i_rwsem);

	if (unlikely(copied < len && !PageUptodate(page))) {
		/*
		 * The page needs to be read in, but that would destroy
		 * our partial write - simplest thing is to just force
		 * userspace to redo the write:
		 */
		zero_user(page, 0, PAGE_SIZE);
		flush_dcache_page(page);
		copied = 0;
	}

	spin_lock(&inode->v.i_lock);
	if (pos + copied > inode->v.i_size)
		i_size_write(&inode->v, pos + copied);
	spin_unlock(&inode->v.i_lock);

	if (copied) {
		if (!PageUptodate(page))
			SetPageUptodate(page);

		bch2_set_page_dirty(c, inode, page, res, offset, copied);

		inode->ei_last_dirtied = (unsigned long) current;
	}

	unlock_page(page);
	put_page(page);
	bch2_pagecache_add_put(&inode->ei_pagecache_lock);

	bch2_page_reservation_put(c, inode, res);
	kfree(res);

	return copied;
}

#define WRITE_BATCH_PAGES	32

static int __bch2_buffered_write(struct bch_inode_info *inode,
				 struct address_space *mapping,
				 struct iov_iter *iter,
				 loff_t pos, unsigned len)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct page *pages[WRITE_BATCH_PAGES];
	struct bch2_page_reservation res;
	unsigned long index = pos >> PAGE_SHIFT;
	unsigned offset = pos & (PAGE_SIZE - 1);
	unsigned nr_pages = DIV_ROUND_UP(offset + len, PAGE_SIZE);
	unsigned i, reserved = 0, set_dirty = 0;
	unsigned copied = 0, nr_pages_copied = 0;
	int ret = 0;

	BUG_ON(!len);
	BUG_ON(nr_pages > ARRAY_SIZE(pages));

	bch2_page_reservation_init(c, inode, &res);

	for (i = 0; i < nr_pages; i++) {
		pages[i] = grab_cache_page_write_begin(mapping, index + i);
		if (!pages[i]) {
			nr_pages = i;
			if (!i) {
				ret = -ENOMEM;
				goto out;
			}
			len = min_t(unsigned, len,
				    nr_pages * PAGE_SIZE - offset);
			break;
		}
	}

	if (offset && !PageUptodate(pages[0])) {
		ret = bch2_read_single_page(pages[0], mapping);
		if (ret)
			goto out;
	}

	if ((pos + len) & (PAGE_SIZE - 1) &&
	    !PageUptodate(pages[nr_pages - 1])) {
		if ((index + nr_pages - 1) << PAGE_SHIFT >= inode->v.i_size) {
			zero_user(pages[nr_pages - 1], 0, PAGE_SIZE);
		} else {
			ret = bch2_read_single_page(pages[nr_pages - 1], mapping);
			if (ret)
				goto out;
		}
	}

	while (reserved < len) {
		unsigned i = (offset + reserved) >> PAGE_SHIFT;
		struct page *page = pages[i];
		unsigned pg_offset = (offset + reserved) & (PAGE_SIZE - 1);
		unsigned pg_len = min_t(unsigned, len - reserved,
					PAGE_SIZE - pg_offset);

		if (!bch2_page_state_create(page, __GFP_NOFAIL)->uptodate) {
			ret = bch2_page_state_set(c, inode_inum(inode),
						  pages + i, nr_pages - i);
			if (ret)
				goto out;
		}

		ret = bch2_page_reservation_get(c, inode, page, &res,
						pg_offset, pg_len);
		if (ret)
			goto out;

		reserved += pg_len;
	}

	if (mapping_writably_mapped(mapping))
		for (i = 0; i < nr_pages; i++)
			flush_dcache_page(pages[i]);

	while (copied < len) {
		struct page *page = pages[(offset + copied) >> PAGE_SHIFT];
		unsigned pg_offset = (offset + copied) & (PAGE_SIZE - 1);
		unsigned pg_len = min_t(unsigned, len - copied,
					PAGE_SIZE - pg_offset);
		unsigned pg_copied = copy_page_from_iter_atomic(page,
						pg_offset, pg_len,iter);

		if (!pg_copied)
			break;

		if (!PageUptodate(page) &&
		    pg_copied != PAGE_SIZE &&
		    pos + copied + pg_copied < inode->v.i_size) {
			zero_user(page, 0, PAGE_SIZE);
			break;
		}

		flush_dcache_page(page);
		copied += pg_copied;

		if (pg_copied != pg_len)
			break;
	}

	if (!copied)
		goto out;

	spin_lock(&inode->v.i_lock);
	if (pos + copied > inode->v.i_size)
		i_size_write(&inode->v, pos + copied);
	spin_unlock(&inode->v.i_lock);

	while (set_dirty < copied) {
		struct page *page = pages[(offset + set_dirty) >> PAGE_SHIFT];
		unsigned pg_offset = (offset + set_dirty) & (PAGE_SIZE - 1);
		unsigned pg_len = min_t(unsigned, copied - set_dirty,
					PAGE_SIZE - pg_offset);

		if (!PageUptodate(page))
			SetPageUptodate(page);

		bch2_set_page_dirty(c, inode, page, &res, pg_offset, pg_len);
		unlock_page(page);
		put_page(page);

		set_dirty += pg_len;
	}

	nr_pages_copied = DIV_ROUND_UP(offset + copied, PAGE_SIZE);
	inode->ei_last_dirtied = (unsigned long) current;
out:
	for (i = nr_pages_copied; i < nr_pages; i++) {
		unlock_page(pages[i]);
		put_page(pages[i]);
	}

	bch2_page_reservation_put(c, inode, &res);

	return copied ?: ret;
}

static ssize_t bch2_buffered_write(struct kiocb *iocb, struct iov_iter *iter)
{
	struct file *file = iocb->ki_filp;
	struct address_space *mapping = file->f_mapping;
	struct bch_inode_info *inode = file_bch_inode(file);
	loff_t pos = iocb->ki_pos;
	ssize_t written = 0;
	int ret = 0;

	bch2_pagecache_add_get(&inode->ei_pagecache_lock);

	do {
		unsigned offset = pos & (PAGE_SIZE - 1);
		unsigned bytes = min_t(unsigned long, iov_iter_count(iter),
			      PAGE_SIZE * WRITE_BATCH_PAGES - offset);
again:
		/*
		 * Bring in the user page that we will copy from _first_.
		 * Otherwise there's a nasty deadlock on copying from the
		 * same page as we're writing to, without it being marked
		 * up-to-date.
		 *
		 * Not only is this an optimisation, but it is also required
		 * to check that the address is actually valid, when atomic
		 * usercopies are used, below.
		 */
		if (unlikely(fault_in_iov_iter_readable(iter, bytes))) {
			bytes = min_t(unsigned long, iov_iter_count(iter),
				      PAGE_SIZE - offset);

			if (unlikely(fault_in_iov_iter_readable(iter, bytes))) {
				ret = -EFAULT;
				break;
			}
		}

		if (unlikely(fatal_signal_pending(current))) {
			ret = -EINTR;
			break;
		}

		ret = __bch2_buffered_write(inode, mapping, iter, pos, bytes);
		if (unlikely(ret < 0))
			break;

		cond_resched();

		if (unlikely(ret == 0)) {
			/*
			 * If we were unable to copy any data at all, we must
			 * fall back to a single segment length write.
			 *
			 * If we didn't fallback here, we could livelock
			 * because not all segments in the iov can be copied at
			 * once without a pagefault.
			 */
			bytes = min_t(unsigned long, PAGE_SIZE - offset,
				      iov_iter_single_seg_count(iter));
			goto again;
		}
		pos += ret;
		written += ret;
		ret = 0;

		balance_dirty_pages_ratelimited(mapping);
	} while (iov_iter_count(iter));

	bch2_pagecache_add_put(&inode->ei_pagecache_lock);

	return written ? written : ret;
}

/* O_DIRECT reads */

static void bio_check_or_release(struct bio *bio, bool check_dirty)
{
	if (check_dirty) {
		bio_check_pages_dirty(bio);
	} else {
		bio_release_pages(bio, false);
		bio_put(bio);
	}
}

static void bch2_dio_read_complete(struct closure *cl)
{
	struct dio_read *dio = container_of(cl, struct dio_read, cl);

	dio->req->ki_complete(dio->req, dio->ret);
	bio_check_or_release(&dio->rbio.bio, dio->should_dirty);
}

static void bch2_direct_IO_read_endio(struct bio *bio)
{
	struct dio_read *dio = bio->bi_private;

	if (bio->bi_status)
		dio->ret = blk_status_to_errno(bio->bi_status);

	closure_put(&dio->cl);
}

static void bch2_direct_IO_read_split_endio(struct bio *bio)
{
	struct dio_read *dio = bio->bi_private;
	bool should_dirty = dio->should_dirty;

	bch2_direct_IO_read_endio(bio);
	bio_check_or_release(bio, should_dirty);
}

static int bch2_direct_IO_read(struct kiocb *req, struct iov_iter *iter)
{
	struct file *file = req->ki_filp;
	struct bch_inode_info *inode = file_bch_inode(file);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bch_io_opts opts = io_opts(c, &inode->ei_inode);
	struct dio_read *dio;
	struct bio *bio;
	loff_t offset = req->ki_pos;
	bool sync = is_sync_kiocb(req);
	size_t shorten;
	ssize_t ret;

	if ((offset|iter->count) & (block_bytes(c) - 1))
		return -EINVAL;

	ret = min_t(loff_t, iter->count,
		    max_t(loff_t, 0, i_size_read(&inode->v) - offset));

	if (!ret)
		return ret;

	shorten = iov_iter_count(iter) - round_up(ret, block_bytes(c));
	iter->count -= shorten;

	bio = bio_alloc_bioset(NULL,
			       bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS),
			       REQ_OP_READ,
			       GFP_KERNEL,
			       &c->dio_read_bioset);

	bio->bi_end_io = bch2_direct_IO_read_endio;

	dio = container_of(bio, struct dio_read, rbio.bio);
	closure_init(&dio->cl, NULL);

	/*
	 * this is a _really_ horrible hack just to avoid an atomic sub at the
	 * end:
	 */
	if (!sync) {
		set_closure_fn(&dio->cl, bch2_dio_read_complete, NULL);
		atomic_set(&dio->cl.remaining,
			   CLOSURE_REMAINING_INITIALIZER -
			   CLOSURE_RUNNING +
			   CLOSURE_DESTRUCTOR);
	} else {
		atomic_set(&dio->cl.remaining,
			   CLOSURE_REMAINING_INITIALIZER + 1);
	}

	dio->req	= req;
	dio->ret	= ret;
	/*
	 * This is one of the sketchier things I've encountered: we have to skip
	 * the dirtying of requests that are internal from the kernel (i.e. from
	 * loopback), because we'll deadlock on page_lock.
	 */
	dio->should_dirty = iter_is_iovec(iter);

	goto start;
	while (iter->count) {
		bio = bio_alloc_bioset(NULL,
				       bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS),
				       REQ_OP_READ,
				       GFP_KERNEL,
				       &c->bio_read);
		bio->bi_end_io		= bch2_direct_IO_read_split_endio;
start:
		bio_set_op_attrs(bio, REQ_OP_READ, REQ_SYNC);
		bio->bi_iter.bi_sector	= offset >> 9;
		bio->bi_private		= dio;

		ret = bio_iov_iter_get_pages(bio, iter);
		if (ret < 0) {
			/* XXX: fault inject this path */
			bio->bi_status = BLK_STS_RESOURCE;
			bio_endio(bio);
			break;
		}

		offset += bio->bi_iter.bi_size;

		if (dio->should_dirty)
			bio_set_pages_dirty(bio);

		if (iter->count)
			closure_get(&dio->cl);

		bch2_read(c, rbio_init(bio, opts), inode_inum(inode));
	}

	iter->count += shorten;

	if (sync) {
		closure_sync(&dio->cl);
		closure_debug_destroy(&dio->cl);
		ret = dio->ret;
		bio_check_or_release(&dio->rbio.bio, dio->should_dirty);
		return ret;
	} else {
		return -EIOCBQUEUED;
	}
}

ssize_t bch2_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
	struct file *file = iocb->ki_filp;
	struct bch_inode_info *inode = file_bch_inode(file);
	struct address_space *mapping = file->f_mapping;
	size_t count = iov_iter_count(iter);
	ssize_t ret;

	if (!count)
		return 0; /* skip atime */

	if (iocb->ki_flags & IOCB_DIRECT) {
		struct blk_plug plug;

		ret = filemap_write_and_wait_range(mapping,
					iocb->ki_pos,
					iocb->ki_pos + count - 1);
		if (ret < 0)
			goto out;

		file_accessed(file);

		blk_start_plug(&plug);
		ret = bch2_direct_IO_read(iocb, iter);
		blk_finish_plug(&plug);

		if (ret >= 0)
			iocb->ki_pos += ret;
	} else {
		bch2_pagecache_add_get(&inode->ei_pagecache_lock);
		ret = generic_file_read_iter(iocb, iter);
		bch2_pagecache_add_put(&inode->ei_pagecache_lock);
	}
out:
	return bch2_err_class(ret);
}

/* O_DIRECT writes */

static bool bch2_check_range_allocated(struct bch_fs *c, subvol_inum inum,
				       u64 offset, u64 size,
				       unsigned nr_replicas, bool compressed)
{
	struct btree_trans trans;
	struct btree_iter iter;
	struct bkey_s_c k;
	u64 end = offset + size;
	u32 snapshot;
	bool ret = true;
	int err;

	bch2_trans_init(&trans, c, 0, 0);
retry:
	bch2_trans_begin(&trans);

	err = bch2_subvolume_get_snapshot(&trans, inum.subvol, &snapshot);
	if (err)
		goto err;

	for_each_btree_key_norestart(&trans, iter, BTREE_ID_extents,
			   SPOS(inum.inum, offset, snapshot),
			   BTREE_ITER_SLOTS, k, err) {
		if (bkey_cmp(bkey_start_pos(k.k), POS(inum.inum, end)) >= 0)
			break;

		if (k.k->p.snapshot != snapshot ||
		    nr_replicas > bch2_bkey_replicas(c, k) ||
		    (!compressed && bch2_bkey_sectors_compressed(k))) {
			ret = false;
			break;
		}
	}

	offset = iter.pos.offset;
	bch2_trans_iter_exit(&trans, &iter);
err:
	if (bch2_err_matches(err, BCH_ERR_transaction_restart))
		goto retry;
	bch2_trans_exit(&trans);

	return err ? false : ret;
}

static void bch2_dio_write_loop_async(struct bch_write_op *);

static long bch2_dio_write_loop(struct dio_write *dio)
{
	bool kthread = (current->flags & PF_KTHREAD) != 0;
	struct kiocb *req = dio->req;
	struct address_space *mapping = req->ki_filp->f_mapping;
	struct bch_inode_info *inode = file_bch_inode(req->ki_filp);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct bio *bio = &dio->op.wbio.bio;
	struct bvec_iter_all iter;
	struct bio_vec *bv;
	unsigned unaligned, iter_count;
	bool sync = dio->sync, dropped_locks;
	long ret;

	if (dio->loop)
		goto loop;

	while (1) {
		iter_count = dio->iter.count;

		if (kthread && dio->mm)
			kthread_use_mm(dio->mm);
		BUG_ON(current->faults_disabled_mapping);
		current->faults_disabled_mapping = mapping;

		ret = bio_iov_iter_get_pages(bio, &dio->iter);

		dropped_locks = fdm_dropped_locks();

		current->faults_disabled_mapping = NULL;
		if (kthread && dio->mm)
			kthread_unuse_mm(dio->mm);

		/*
		 * If the fault handler returned an error but also signalled
		 * that it dropped & retook ei_pagecache_lock, we just need to
		 * re-shoot down the page cache and retry:
		 */
		if (dropped_locks && ret)
			ret = 0;

		if (unlikely(ret < 0))
			goto err;

		if (unlikely(dropped_locks)) {
			ret = write_invalidate_inode_pages_range(mapping,
					req->ki_pos,
					req->ki_pos + iter_count - 1);
			if (unlikely(ret))
				goto err;

			if (!bio->bi_iter.bi_size)
				continue;
		}

		unaligned = bio->bi_iter.bi_size & (block_bytes(c) - 1);
		bio->bi_iter.bi_size -= unaligned;
		iov_iter_revert(&dio->iter, unaligned);

		if (!bio->bi_iter.bi_size) {
			/*
			 * bio_iov_iter_get_pages was only able to get <
			 * blocksize worth of pages:
			 */
			ret = -EFAULT;
			goto err;
		}

		bch2_write_op_init(&dio->op, c, io_opts(c, &inode->ei_inode));
		dio->op.end_io		= bch2_dio_write_loop_async;
		dio->op.target		= dio->op.opts.foreground_target;
		dio->op.write_point	= writepoint_hashed((unsigned long) current);
		dio->op.nr_replicas	= dio->op.opts.data_replicas;
		dio->op.subvol		= inode->ei_subvol;
		dio->op.pos		= POS(inode->v.i_ino, (u64) req->ki_pos >> 9);

		if ((req->ki_flags & IOCB_DSYNC) &&
		    !c->opts.journal_flush_disabled)
			dio->op.flags |= BCH_WRITE_FLUSH;
		dio->op.flags |= BCH_WRITE_CHECK_ENOSPC;

		ret = bch2_disk_reservation_get(c, &dio->op.res, bio_sectors(bio),
						dio->op.opts.data_replicas, 0);
		if (unlikely(ret) &&
		    !bch2_check_range_allocated(c, inode_inum(inode),
				dio->op.pos.offset, bio_sectors(bio),
				dio->op.opts.data_replicas,
				dio->op.opts.compression != 0))
			goto err;

		task_io_account_write(bio->bi_iter.bi_size);

		if (!dio->sync && !dio->loop && dio->iter.count) {
			struct iovec *iov = dio->inline_vecs;

			if (dio->iter.nr_segs > ARRAY_SIZE(dio->inline_vecs)) {
				iov = kmalloc(dio->iter.nr_segs * sizeof(*iov),
					      GFP_KERNEL);
				if (unlikely(!iov)) {
					dio->sync = sync = true;
					goto do_io;
				}

				dio->free_iov = true;
			}

			memcpy(iov, dio->iter.iov, dio->iter.nr_segs * sizeof(*iov));
			dio->iter.iov = iov;
		}
do_io:
		dio->loop = true;
		closure_call(&dio->op.cl, bch2_write, NULL, NULL);

		if (sync)
			wait_for_completion(&dio->done);
		else
			return -EIOCBQUEUED;
loop:
		i_sectors_acct(c, inode, &dio->quota_res,
			       dio->op.i_sectors_delta);
		req->ki_pos += (u64) dio->op.written << 9;
		dio->written += dio->op.written;

		spin_lock(&inode->v.i_lock);
		if (req->ki_pos > inode->v.i_size)
			i_size_write(&inode->v, req->ki_pos);
		spin_unlock(&inode->v.i_lock);

		if (likely(!bio_flagged(bio, BIO_NO_PAGE_REF)))
			bio_for_each_segment_all(bv, bio, iter)
				put_page(bv->bv_page);
		bio->bi_vcnt = 0;

		if (dio->op.error) {
			set_bit(EI_INODE_ERROR, &inode->ei_flags);
			break;
		}

		if (!dio->iter.count)
			break;

		bio_reset(bio, NULL, REQ_OP_WRITE);
		reinit_completion(&dio->done);
	}

	ret = dio->op.error ?: ((long) dio->written << 9);
err:
	bch2_pagecache_block_put(&inode->ei_pagecache_lock);
	bch2_quota_reservation_put(c, inode, &dio->quota_res);

	if (dio->free_iov)
		kfree(dio->iter.iov);

	if (likely(!bio_flagged(bio, BIO_NO_PAGE_REF)))
		bio_for_each_segment_all(bv, bio, iter)
			put_page(bv->bv_page);
	bio_put(bio);

	/* inode->i_dio_count is our ref on inode and thus bch_fs */
	inode_dio_end(&inode->v);

	if (ret < 0)
		ret = bch2_err_class(ret);

	if (!sync) {
		req->ki_complete(req, ret);
		ret = -EIOCBQUEUED;
	}
	return ret;
}

static void bch2_dio_write_loop_async(struct bch_write_op *op)
{
	struct dio_write *dio = container_of(op, struct dio_write, op);

	if (dio->sync)
		complete(&dio->done);
	else
		bch2_dio_write_loop(dio);
}

static noinline
ssize_t bch2_direct_write(struct kiocb *req, struct iov_iter *iter)
{
	struct file *file = req->ki_filp;
	struct address_space *mapping = file->f_mapping;
	struct bch_inode_info *inode = file_bch_inode(file);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct dio_write *dio;
	struct bio *bio;
	bool locked = true, extending;
	ssize_t ret;

	prefetch(&c->opts);
	prefetch((void *) &c->opts + 64);
	prefetch(&inode->ei_inode);
	prefetch((void *) &inode->ei_inode + 64);

	inode_lock(&inode->v);

	ret = generic_write_checks(req, iter);
	if (unlikely(ret <= 0))
		goto err;

	ret = file_remove_privs(file);
	if (unlikely(ret))
		goto err;

	ret = file_update_time(file);
	if (unlikely(ret))
		goto err;

	if (unlikely((req->ki_pos|iter->count) & (block_bytes(c) - 1)))
		goto err;

	inode_dio_begin(&inode->v);
	bch2_pagecache_block_get(&inode->ei_pagecache_lock);

	extending = req->ki_pos + iter->count > inode->v.i_size;
	if (!extending) {
		inode_unlock(&inode->v);
		locked = false;
	}

	bio = bio_alloc_bioset(NULL,
			       bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS),
			       REQ_OP_WRITE,
			       GFP_KERNEL,
			       &c->dio_write_bioset);
	dio = container_of(bio, struct dio_write, op.wbio.bio);
	init_completion(&dio->done);
	dio->req		= req;
	dio->mm			= current->mm;
	dio->loop		= false;
	dio->sync		= is_sync_kiocb(req) || extending;
	dio->free_iov		= false;
	dio->quota_res.sectors	= 0;
	dio->written		= 0;
	dio->iter		= *iter;

	ret = bch2_quota_reservation_add(c, inode, &dio->quota_res,
					 iter->count >> 9, true);
	if (unlikely(ret))
		goto err_put_bio;

	ret = write_invalidate_inode_pages_range(mapping,
					req->ki_pos,
					req->ki_pos + iter->count - 1);
	if (unlikely(ret))
		goto err_put_bio;

	ret = bch2_dio_write_loop(dio);
err:
	if (locked)
		inode_unlock(&inode->v);
	return ret;
err_put_bio:
	bch2_pagecache_block_put(&inode->ei_pagecache_lock);
	bch2_quota_reservation_put(c, inode, &dio->quota_res);
	bio_put(bio);
	inode_dio_end(&inode->v);
	goto err;
}

ssize_t bch2_write_iter(struct kiocb *iocb, struct iov_iter *from)
{
	struct file *file = iocb->ki_filp;
	struct bch_inode_info *inode = file_bch_inode(file);
	ssize_t ret;

	if (iocb->ki_flags & IOCB_DIRECT) {
		ret = bch2_direct_write(iocb, from);
		goto out;
	}

	/* We can write back this queue in page reclaim */
	current->backing_dev_info = inode_to_bdi(&inode->v);
	inode_lock(&inode->v);

	ret = generic_write_checks(iocb, from);
	if (ret <= 0)
		goto unlock;

	ret = file_remove_privs(file);
	if (ret)
		goto unlock;

	ret = file_update_time(file);
	if (ret)
		goto unlock;

	ret = bch2_buffered_write(iocb, from);
	if (likely(ret > 0))
		iocb->ki_pos += ret;
unlock:
	inode_unlock(&inode->v);
	current->backing_dev_info = NULL;

	if (ret > 0)
		ret = generic_write_sync(iocb, ret);
out:
	return bch2_err_class(ret);
}

/* fsync: */

/*
 * inode->ei_inode.bi_journal_seq won't be up to date since it's set in an
 * insert trigger: look up the btree inode instead
 */
static int bch2_flush_inode(struct bch_fs *c, subvol_inum inum)
{
	struct bch_inode_unpacked inode;
	int ret;

	if (c->opts.journal_flush_disabled)
		return 0;

	ret = bch2_inode_find_by_inum(c, inum, &inode);
	if (ret)
		return ret;

	return bch2_journal_flush_seq(&c->journal, inode.bi_journal_seq);
}

int bch2_fsync(struct file *file, loff_t start, loff_t end, int datasync)
{
	struct bch_inode_info *inode = file_bch_inode(file);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	int ret, ret2, ret3;

	ret = file_write_and_wait_range(file, start, end);
	ret2 = sync_inode_metadata(&inode->v, 1);
	ret3 = bch2_flush_inode(c, inode_inum(inode));

	return bch2_err_class(ret ?: ret2 ?: ret3);
}

/* truncate: */

static inline int range_has_data(struct bch_fs *c, u32 subvol,
				 struct bpos start,
				 struct bpos end)
{
	struct btree_trans trans;
	struct btree_iter iter;
	struct bkey_s_c k;
	int ret = 0;

	bch2_trans_init(&trans, c, 0, 0);
retry:
	bch2_trans_begin(&trans);

	ret = bch2_subvolume_get_snapshot(&trans, subvol, &start.snapshot);
	if (ret)
		goto err;

	for_each_btree_key_norestart(&trans, iter, BTREE_ID_extents, start, 0, k, ret) {
		if (bkey_cmp(bkey_start_pos(k.k), end) >= 0)
			break;

		if (bkey_extent_is_data(k.k)) {
			ret = 1;
			break;
		}
	}
	start = iter.pos;
	bch2_trans_iter_exit(&trans, &iter);
err:
	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
		goto retry;

	bch2_trans_exit(&trans);
	return ret;
}

static int __bch2_truncate_page(struct bch_inode_info *inode,
				pgoff_t index, loff_t start, loff_t end)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct address_space *mapping = inode->v.i_mapping;
	struct bch_page_state *s;
	unsigned start_offset = start & (PAGE_SIZE - 1);
	unsigned end_offset = ((end - 1) & (PAGE_SIZE - 1)) + 1;
	unsigned i;
	struct page *page;
	s64 i_sectors_delta = 0;
	int ret = 0;

	/* Page boundary? Nothing to do */
	if (!((index == start >> PAGE_SHIFT && start_offset) ||
	      (index == end >> PAGE_SHIFT && end_offset != PAGE_SIZE)))
		return 0;

	/* Above i_size? */
	if (index << PAGE_SHIFT >= inode->v.i_size)
		return 0;

	page = find_lock_page(mapping, index);
	if (!page) {
		/*
		 * XXX: we're doing two index lookups when we end up reading the
		 * page
		 */
		ret = range_has_data(c, inode->ei_subvol,
				POS(inode->v.i_ino, index << PAGE_SECTORS_SHIFT),
				POS(inode->v.i_ino, (index + 1) << PAGE_SECTORS_SHIFT));
		if (ret <= 0)
			return ret;

		page = find_or_create_page(mapping, index, GFP_KERNEL);
		if (unlikely(!page)) {
			ret = -ENOMEM;
			goto out;
		}
	}

	s = bch2_page_state_create(page, 0);
	if (!s) {
		ret = -ENOMEM;
		goto unlock;
	}

	if (!PageUptodate(page)) {
		ret = bch2_read_single_page(page, mapping);
		if (ret)
			goto unlock;
	}

	if (index != start >> PAGE_SHIFT)
		start_offset = 0;
	if (index != end >> PAGE_SHIFT)
		end_offset = PAGE_SIZE;

	for (i = round_up(start_offset, block_bytes(c)) >> 9;
	     i < round_down(end_offset, block_bytes(c)) >> 9;
	     i++) {
		s->s[i].nr_replicas	= 0;
		if (s->s[i].state == SECTOR_DIRTY)
			i_sectors_delta--;
		s->s[i].state		= SECTOR_UNALLOCATED;
	}

	i_sectors_acct(c, inode, NULL, i_sectors_delta);

	/*
	 * Caller needs to know whether this page will be written out by
	 * writeback - doing an i_size update if necessary - or whether it will
	 * be responsible for the i_size update:
	 */
	ret = s->s[(min_t(u64, inode->v.i_size - (index << PAGE_SHIFT),
			  PAGE_SIZE) - 1) >> 9].state >= SECTOR_DIRTY;

	zero_user_segment(page, start_offset, end_offset);

	/*
	 * Bit of a hack - we don't want truncate to fail due to -ENOSPC.
	 *
	 * XXX: because we aren't currently tracking whether the page has actual
	 * data in it (vs. just 0s, or only partially written) this wrong. ick.
	 */
	BUG_ON(bch2_get_page_disk_reservation(c, inode, page, false));

	/*
	 * This removes any writeable userspace mappings; we need to force
	 * .page_mkwrite to be called again before any mmapped writes, to
	 * redirty the full page:
	 */
	page_mkclean(page);
	__set_page_dirty_nobuffers(page);
unlock:
	unlock_page(page);
	put_page(page);
out:
	return ret;
}

static int bch2_truncate_page(struct bch_inode_info *inode, loff_t from)
{
	return __bch2_truncate_page(inode, from >> PAGE_SHIFT,
				    from, round_up(from, PAGE_SIZE));
}

static int bch2_truncate_pages(struct bch_inode_info *inode,
			       loff_t start, loff_t end)
{
	int ret = __bch2_truncate_page(inode, start >> PAGE_SHIFT,
				       start, end);

	if (ret >= 0 &&
	    start >> PAGE_SHIFT != end >> PAGE_SHIFT)
		ret = __bch2_truncate_page(inode,
					   end >> PAGE_SHIFT,
					   start, end);
	return ret;
}

static int bch2_extend(struct user_namespace *mnt_userns,
		       struct bch_inode_info *inode,
		       struct bch_inode_unpacked *inode_u,
		       struct iattr *iattr)
{
	struct address_space *mapping = inode->v.i_mapping;
	int ret;

	/*
	 * sync appends:
	 *
	 * this has to be done _before_ extending i_size:
	 */
	ret = filemap_write_and_wait_range(mapping, inode_u->bi_size, S64_MAX);
	if (ret)
		return ret;

	truncate_setsize(&inode->v, iattr->ia_size);

	return bch2_setattr_nonsize(mnt_userns, inode, iattr);
}

static int bch2_truncate_finish_fn(struct bch_inode_info *inode,
				   struct bch_inode_unpacked *bi,
				   void *p)
{
	bi->bi_flags &= ~BCH_INODE_I_SIZE_DIRTY;
	return 0;
}

static int bch2_truncate_start_fn(struct bch_inode_info *inode,
				  struct bch_inode_unpacked *bi, void *p)
{
	u64 *new_i_size = p;

	bi->bi_flags |= BCH_INODE_I_SIZE_DIRTY;
	bi->bi_size = *new_i_size;
	return 0;
}

int bch2_truncate(struct user_namespace *mnt_userns,
		  struct bch_inode_info *inode, struct iattr *iattr)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct address_space *mapping = inode->v.i_mapping;
	struct bch_inode_unpacked inode_u;
	u64 new_i_size = iattr->ia_size;
	s64 i_sectors_delta = 0;
	int ret = 0;

	/*
	 * If the truncate call with change the size of the file, the
	 * cmtimes should be updated. If the size will not change, we
	 * do not need to update the cmtimes.
	 */
	if (iattr->ia_size != inode->v.i_size) {
		if (!(iattr->ia_valid & ATTR_MTIME))
			ktime_get_coarse_real_ts64(&iattr->ia_mtime);
		if (!(iattr->ia_valid & ATTR_CTIME))
			ktime_get_coarse_real_ts64(&iattr->ia_ctime);
		iattr->ia_valid |= ATTR_MTIME|ATTR_CTIME;
	}

	inode_dio_wait(&inode->v);
	bch2_pagecache_block_get(&inode->ei_pagecache_lock);

	ret = bch2_inode_find_by_inum(c, inode_inum(inode), &inode_u);
	if (ret)
		goto err;

	/*
	 * check this before next assertion; on filesystem error our normal
	 * invariants are a bit broken (truncate has to truncate the page cache
	 * before the inode).
	 */
	ret = bch2_journal_error(&c->journal);
	if (ret)
		goto err;

	WARN_ON(!test_bit(EI_INODE_ERROR, &inode->ei_flags) &&
		inode->v.i_size < inode_u.bi_size);

	if (iattr->ia_size > inode->v.i_size) {
		ret = bch2_extend(mnt_userns, inode, &inode_u, iattr);
		goto err;
	}

	iattr->ia_valid &= ~ATTR_SIZE;

	ret = bch2_truncate_page(inode, iattr->ia_size);
	if (unlikely(ret < 0))
		goto err;

	/*
	 * When extending, we're going to write the new i_size to disk
	 * immediately so we need to flush anything above the current on disk
	 * i_size first:
	 *
	 * Also, when extending we need to flush the page that i_size currently
	 * straddles - if it's mapped to userspace, we need to ensure that
	 * userspace has to redirty it and call .mkwrite -> set_page_dirty
	 * again to allocate the part of the page that was extended.
	 */
	if (iattr->ia_size > inode_u.bi_size)
		ret = filemap_write_and_wait_range(mapping,
				inode_u.bi_size,
				iattr->ia_size - 1);
	else if (iattr->ia_size & (PAGE_SIZE - 1))
		ret = filemap_write_and_wait_range(mapping,
				round_down(iattr->ia_size, PAGE_SIZE),
				iattr->ia_size - 1);
	if (ret)
		goto err;

	mutex_lock(&inode->ei_update_lock);
	ret = bch2_write_inode(c, inode, bch2_truncate_start_fn,
			       &new_i_size, 0);
	mutex_unlock(&inode->ei_update_lock);

	if (unlikely(ret))
		goto err;

	truncate_setsize(&inode->v, iattr->ia_size);

	ret = bch2_fpunch(c, inode_inum(inode),
			round_up(iattr->ia_size, block_bytes(c)) >> 9,
			U64_MAX, &i_sectors_delta);
	i_sectors_acct(c, inode, NULL, i_sectors_delta);

	bch2_fs_inconsistent_on(!inode->v.i_size && inode->v.i_blocks &&
				!bch2_journal_error(&c->journal), c,
				"inode %lu truncated to 0 but i_blocks %llu (ondisk %lli)",
				inode->v.i_ino, (u64) inode->v.i_blocks,
				inode->ei_inode.bi_sectors);
	if (unlikely(ret))
		goto err;

	mutex_lock(&inode->ei_update_lock);
	ret = bch2_write_inode(c, inode, bch2_truncate_finish_fn, NULL, 0);
	mutex_unlock(&inode->ei_update_lock);

	ret = bch2_setattr_nonsize(mnt_userns, inode, iattr);
err:
	bch2_pagecache_block_put(&inode->ei_pagecache_lock);
	return bch2_err_class(ret);
}

/* fallocate: */

static int inode_update_times_fn(struct bch_inode_info *inode,
				 struct bch_inode_unpacked *bi, void *p)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;

	bi->bi_mtime = bi->bi_ctime = bch2_current_time(c);
	return 0;
}

static long bchfs_fpunch(struct bch_inode_info *inode, loff_t offset, loff_t len)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	u64 end		= offset + len;
	u64 block_start	= round_up(offset, block_bytes(c));
	u64 block_end	= round_down(end, block_bytes(c));
	bool truncated_last_page;
	int ret = 0;

	ret = bch2_truncate_pages(inode, offset, end);
	if (unlikely(ret < 0))
		goto err;

	truncated_last_page = ret;

	truncate_pagecache_range(&inode->v, offset, end - 1);

	if (block_start < block_end ) {
		s64 i_sectors_delta = 0;

		ret = bch2_fpunch(c, inode_inum(inode),
				  block_start >> 9, block_end >> 9,
				  &i_sectors_delta);
		i_sectors_acct(c, inode, NULL, i_sectors_delta);
	}

	mutex_lock(&inode->ei_update_lock);
	if (end >= inode->v.i_size && !truncated_last_page) {
		ret = bch2_write_inode_size(c, inode, inode->v.i_size,
					    ATTR_MTIME|ATTR_CTIME);
	} else {
		ret = bch2_write_inode(c, inode, inode_update_times_fn, NULL,
				       ATTR_MTIME|ATTR_CTIME);
	}
	mutex_unlock(&inode->ei_update_lock);
err:
	return ret;
}

static long bchfs_fcollapse_finsert(struct bch_inode_info *inode,
				   loff_t offset, loff_t len,
				   bool insert)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct address_space *mapping = inode->v.i_mapping;
	struct bkey_buf copy;
	struct btree_trans trans;
	struct btree_iter src, dst, del;
	loff_t shift, new_size;
	u64 src_start;
	int ret = 0;

	if ((offset | len) & (block_bytes(c) - 1))
		return -EINVAL;

	if (insert) {
		if (inode->v.i_sb->s_maxbytes - inode->v.i_size < len)
			return -EFBIG;

		if (offset >= inode->v.i_size)
			return -EINVAL;

		src_start	= U64_MAX;
		shift		= len;
	} else {
		if (offset + len >= inode->v.i_size)
			return -EINVAL;

		src_start	= offset + len;
		shift		= -len;
	}

	new_size = inode->v.i_size + shift;

	ret = write_invalidate_inode_pages_range(mapping, offset, LLONG_MAX);
	if (ret)
		return ret;

	if (insert) {
		i_size_write(&inode->v, new_size);
		mutex_lock(&inode->ei_update_lock);
		ret = bch2_write_inode_size(c, inode, new_size,
					    ATTR_MTIME|ATTR_CTIME);
		mutex_unlock(&inode->ei_update_lock);
	} else {
		s64 i_sectors_delta = 0;

		ret = bch2_fpunch(c, inode_inum(inode),
				  offset >> 9, (offset + len) >> 9,
				  &i_sectors_delta);
		i_sectors_acct(c, inode, NULL, i_sectors_delta);

		if (ret)
			return ret;
	}

	bch2_bkey_buf_init(&copy);
	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 1024);
	bch2_trans_iter_init(&trans, &src, BTREE_ID_extents,
			POS(inode->v.i_ino, src_start >> 9),
			BTREE_ITER_INTENT);
	bch2_trans_copy_iter(&dst, &src);
	bch2_trans_copy_iter(&del, &src);

	while (ret == 0 ||
	       bch2_err_matches(ret, BCH_ERR_transaction_restart)) {
		struct disk_reservation disk_res =
			bch2_disk_reservation_init(c, 0);
		struct bkey_i delete;
		struct bkey_s_c k;
		struct bpos next_pos;
		struct bpos move_pos = POS(inode->v.i_ino, offset >> 9);
		struct bpos atomic_end;
		unsigned trigger_flags = 0;
		u32 snapshot;

		bch2_trans_begin(&trans);

		ret = bch2_subvolume_get_snapshot(&trans,
					inode->ei_subvol, &snapshot);
		if (ret)
			continue;

		bch2_btree_iter_set_snapshot(&src, snapshot);
		bch2_btree_iter_set_snapshot(&dst, snapshot);
		bch2_btree_iter_set_snapshot(&del, snapshot);

		bch2_trans_begin(&trans);

		k = insert
			? bch2_btree_iter_peek_prev(&src)
			: bch2_btree_iter_peek(&src);
		if ((ret = bkey_err(k)))
			continue;

		if (!k.k || k.k->p.inode != inode->v.i_ino)
			break;

		if (insert &&
		    bkey_cmp(k.k->p, POS(inode->v.i_ino, offset >> 9)) <= 0)
			break;
reassemble:
		bch2_bkey_buf_reassemble(&copy, c, k);

		if (insert &&
		    bkey_cmp(bkey_start_pos(k.k), move_pos) < 0)
			bch2_cut_front(move_pos, copy.k);

		copy.k->k.p.offset += shift >> 9;
		bch2_btree_iter_set_pos(&dst, bkey_start_pos(&copy.k->k));

		ret = bch2_extent_atomic_end(&trans, &dst, copy.k, &atomic_end);
		if (ret)
			continue;

		if (bkey_cmp(atomic_end, copy.k->k.p)) {
			if (insert) {
				move_pos = atomic_end;
				move_pos.offset -= shift >> 9;
				goto reassemble;
			} else {
				bch2_cut_back(atomic_end, copy.k);
			}
		}

		bkey_init(&delete.k);
		delete.k.p = copy.k->k.p;
		delete.k.size = copy.k->k.size;
		delete.k.p.offset -= shift >> 9;
		bch2_btree_iter_set_pos(&del, bkey_start_pos(&delete.k));

		next_pos = insert ? bkey_start_pos(&delete.k) : delete.k.p;

		if (copy.k->k.size != k.k->size) {
			/* We might end up splitting compressed extents: */
			unsigned nr_ptrs =
				bch2_bkey_nr_ptrs_allocated(bkey_i_to_s_c(copy.k));

			ret = bch2_disk_reservation_get(c, &disk_res,
					copy.k->k.size, nr_ptrs,
					BCH_DISK_RESERVATION_NOFAIL);
			BUG_ON(ret);
		}

		ret =   bch2_btree_iter_traverse(&del) ?:
			bch2_trans_update(&trans, &del, &delete, trigger_flags) ?:
			bch2_trans_update(&trans, &dst, copy.k, trigger_flags) ?:
			bch2_trans_commit(&trans, &disk_res, NULL,
					  BTREE_INSERT_NOFAIL);
		bch2_disk_reservation_put(c, &disk_res);

		if (!ret)
			bch2_btree_iter_set_pos(&src, next_pos);
	}
	bch2_trans_iter_exit(&trans, &del);
	bch2_trans_iter_exit(&trans, &dst);
	bch2_trans_iter_exit(&trans, &src);
	bch2_trans_exit(&trans);
	bch2_bkey_buf_exit(&copy, c);

	if (ret)
		return ret;

	mutex_lock(&inode->ei_update_lock);
	if (!insert) {
		i_size_write(&inode->v, new_size);
		ret = bch2_write_inode_size(c, inode, new_size,
					    ATTR_MTIME|ATTR_CTIME);
	} else {
		/* We need an inode update to update bi_journal_seq for fsync: */
		ret = bch2_write_inode(c, inode, inode_update_times_fn, NULL,
				       ATTR_MTIME|ATTR_CTIME);
	}
	mutex_unlock(&inode->ei_update_lock);
	return ret;
}

static int __bchfs_fallocate(struct bch_inode_info *inode, int mode,
			     u64 start_sector, u64 end_sector)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct btree_trans trans;
	struct btree_iter iter;
	struct bpos end_pos = POS(inode->v.i_ino, end_sector);
	unsigned replicas = io_opts(c, &inode->ei_inode).data_replicas;
	int ret = 0;

	bch2_trans_init(&trans, c, BTREE_ITER_MAX, 512);

	bch2_trans_iter_init(&trans, &iter, BTREE_ID_extents,
			POS(inode->v.i_ino, start_sector),
			BTREE_ITER_SLOTS|BTREE_ITER_INTENT);

	while (!ret && bkey_cmp(iter.pos, end_pos) < 0) {
		s64 i_sectors_delta = 0;
		struct disk_reservation disk_res = { 0 };
		struct quota_res quota_res = { 0 };
		struct bkey_i_reservation reservation;
		struct bkey_s_c k;
		unsigned sectors;
		u32 snapshot;

		bch2_trans_begin(&trans);

		ret = bch2_subvolume_get_snapshot(&trans,
					inode->ei_subvol, &snapshot);
		if (ret)
			goto bkey_err;

		bch2_btree_iter_set_snapshot(&iter, snapshot);

		k = bch2_btree_iter_peek_slot(&iter);
		if ((ret = bkey_err(k)))
			goto bkey_err;

		/* already reserved */
		if (k.k->type == KEY_TYPE_reservation &&
		    bkey_s_c_to_reservation(k).v->nr_replicas >= replicas) {
			bch2_btree_iter_advance(&iter);
			continue;
		}

		if (bkey_extent_is_data(k.k) &&
		    !(mode & FALLOC_FL_ZERO_RANGE)) {
			bch2_btree_iter_advance(&iter);
			continue;
		}

		bkey_reservation_init(&reservation.k_i);
		reservation.k.type	= KEY_TYPE_reservation;
		reservation.k.p		= k.k->p;
		reservation.k.size	= k.k->size;

		bch2_cut_front(iter.pos,	&reservation.k_i);
		bch2_cut_back(end_pos,		&reservation.k_i);

		sectors = reservation.k.size;
		reservation.v.nr_replicas = bch2_bkey_nr_ptrs_allocated(k);

		if (!bkey_extent_is_allocation(k.k)) {
			ret = bch2_quota_reservation_add(c, inode,
					&quota_res,
					sectors, true);
			if (unlikely(ret))
				goto bkey_err;
		}

		if (reservation.v.nr_replicas < replicas ||
		    bch2_bkey_sectors_compressed(k)) {
			ret = bch2_disk_reservation_get(c, &disk_res, sectors,
							replicas, 0);
			if (unlikely(ret))
				goto bkey_err;

			reservation.v.nr_replicas = disk_res.nr_replicas;
		}

		ret = bch2_extent_update(&trans, inode_inum(inode), &iter,
					 &reservation.k_i,
				&disk_res, NULL,
				0, &i_sectors_delta, true);
		if (ret)
			goto bkey_err;
		i_sectors_acct(c, inode, &quota_res, i_sectors_delta);
bkey_err:
		bch2_quota_reservation_put(c, inode, &quota_res);
		bch2_disk_reservation_put(c, &disk_res);
		if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
			ret = 0;
	}

	bch2_trans_unlock(&trans); /* lock ordering, before taking pagecache locks: */
	mark_pagecache_reserved(inode, start_sector, iter.pos.offset);

	if (bch2_err_matches(ret, ENOSPC) && (mode & FALLOC_FL_ZERO_RANGE)) {
		struct quota_res quota_res = { 0 };
		s64 i_sectors_delta = 0;

		bch2_fpunch_at(&trans, &iter, inode_inum(inode),
			       end_sector, &i_sectors_delta);
		i_sectors_acct(c, inode, &quota_res, i_sectors_delta);
		bch2_quota_reservation_put(c, inode, &quota_res);
	}

	bch2_trans_iter_exit(&trans, &iter);
	bch2_trans_exit(&trans);
	return ret;
}

static long bchfs_fallocate(struct bch_inode_info *inode, int mode,
			    loff_t offset, loff_t len)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	u64 end		= offset + len;
	u64 block_start	= round_down(offset,	block_bytes(c));
	u64 block_end	= round_up(end,		block_bytes(c));
	bool truncated_last_page = false;
	int ret, ret2 = 0;

	if (!(mode & FALLOC_FL_KEEP_SIZE) && end > inode->v.i_size) {
		ret = inode_newsize_ok(&inode->v, end);
		if (ret)
			return ret;
	}

	if (mode & FALLOC_FL_ZERO_RANGE) {
		ret = bch2_truncate_pages(inode, offset, end);
		if (unlikely(ret < 0))
			return ret;

		truncated_last_page = ret;

		truncate_pagecache_range(&inode->v, offset, end - 1);

		block_start	= round_up(offset,	block_bytes(c));
		block_end	= round_down(end,	block_bytes(c));
	}

	ret = __bchfs_fallocate(inode, mode, block_start >> 9, block_end >> 9);

	/*
	 * On -ENOSPC in ZERO_RANGE mode, we still want to do the inode update,
	 * so that the VFS cache i_size is consistent with the btree i_size:
	 */
	if (ret &&
	    !(bch2_err_matches(ret, ENOSPC) && (mode & FALLOC_FL_ZERO_RANGE)))
		return ret;

	if (mode & FALLOC_FL_KEEP_SIZE && end > inode->v.i_size)
		end = inode->v.i_size;

	if (end >= inode->v.i_size &&
	    (((mode & FALLOC_FL_ZERO_RANGE) && !truncated_last_page) ||
	     !(mode & FALLOC_FL_KEEP_SIZE))) {
		spin_lock(&inode->v.i_lock);
		i_size_write(&inode->v, end);
		spin_unlock(&inode->v.i_lock);

		mutex_lock(&inode->ei_update_lock);
		ret2 = bch2_write_inode_size(c, inode, end, 0);
		mutex_unlock(&inode->ei_update_lock);
	}

	return ret ?: ret2;
}

long bch2_fallocate_dispatch(struct file *file, int mode,
			     loff_t offset, loff_t len)
{
	struct bch_inode_info *inode = file_bch_inode(file);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	long ret;

	if (!percpu_ref_tryget_live(&c->writes))
		return -EROFS;

	inode_lock(&inode->v);
	inode_dio_wait(&inode->v);
	bch2_pagecache_block_get(&inode->ei_pagecache_lock);

	ret = file_modified(file);
	if (ret)
		goto err;

	if (!(mode & ~(FALLOC_FL_KEEP_SIZE|FALLOC_FL_ZERO_RANGE)))
		ret = bchfs_fallocate(inode, mode, offset, len);
	else if (mode == (FALLOC_FL_PUNCH_HOLE|FALLOC_FL_KEEP_SIZE))
		ret = bchfs_fpunch(inode, offset, len);
	else if (mode == FALLOC_FL_INSERT_RANGE)
		ret = bchfs_fcollapse_finsert(inode, offset, len, true);
	else if (mode == FALLOC_FL_COLLAPSE_RANGE)
		ret = bchfs_fcollapse_finsert(inode, offset, len, false);
	else
		ret = -EOPNOTSUPP;
err:
	bch2_pagecache_block_put(&inode->ei_pagecache_lock);
	inode_unlock(&inode->v);
	percpu_ref_put(&c->writes);

	return bch2_err_class(ret);
}

static int quota_reserve_range(struct bch_inode_info *inode,
			       struct quota_res *res,
			       u64 start, u64 end)
{
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct btree_trans trans;
	struct btree_iter iter;
	struct bkey_s_c k;
	u32 snapshot;
	u64 sectors = end - start;
	u64 pos = start;
	int ret;

	bch2_trans_init(&trans, c, 0, 0);
retry:
	bch2_trans_begin(&trans);

	ret = bch2_subvolume_get_snapshot(&trans, inode->ei_subvol, &snapshot);
	if (ret)
		goto err;

	bch2_trans_iter_init(&trans, &iter, BTREE_ID_extents,
			     SPOS(inode->v.i_ino, pos, snapshot), 0);

	while (!(ret = btree_trans_too_many_iters(&trans)) &&
	       (k = bch2_btree_iter_peek_upto(&iter, POS(inode->v.i_ino, end - 1))).k &&
	       !(ret = bkey_err(k))) {
		if (bkey_extent_is_allocation(k.k)) {
			u64 s = min(end, k.k->p.offset) -
				max(start, bkey_start_offset(k.k));
			BUG_ON(s > sectors);
			sectors -= s;
		}
		bch2_btree_iter_advance(&iter);
	}
	pos = iter.pos.offset;
	bch2_trans_iter_exit(&trans, &iter);
err:
	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
		goto retry;

	bch2_trans_exit(&trans);

	if (ret)
		return ret;

	return bch2_quota_reservation_add(c, inode, res, sectors, true);
}

loff_t bch2_remap_file_range(struct file *file_src, loff_t pos_src,
			     struct file *file_dst, loff_t pos_dst,
			     loff_t len, unsigned remap_flags)
{
	struct bch_inode_info *src = file_bch_inode(file_src);
	struct bch_inode_info *dst = file_bch_inode(file_dst);
	struct bch_fs *c = src->v.i_sb->s_fs_info;
	struct quota_res quota_res = { 0 };
	s64 i_sectors_delta = 0;
	u64 aligned_len;
	loff_t ret = 0;

	if (remap_flags & ~(REMAP_FILE_DEDUP|REMAP_FILE_ADVISORY))
		return -EINVAL;

	if (remap_flags & REMAP_FILE_DEDUP)
		return -EOPNOTSUPP;

	if ((pos_src & (block_bytes(c) - 1)) ||
	    (pos_dst & (block_bytes(c) - 1)))
		return -EINVAL;

	if (src == dst &&
	    abs(pos_src - pos_dst) < len)
		return -EINVAL;

	bch2_lock_inodes(INODE_LOCK|INODE_PAGECACHE_BLOCK, src, dst);

	inode_dio_wait(&src->v);
	inode_dio_wait(&dst->v);

	ret = generic_remap_file_range_prep(file_src, pos_src,
					    file_dst, pos_dst,
					    &len, remap_flags);
	if (ret < 0 || len == 0)
		goto err;

	aligned_len = round_up((u64) len, block_bytes(c));

	ret = write_invalidate_inode_pages_range(dst->v.i_mapping,
				pos_dst, pos_dst + len - 1);
	if (ret)
		goto err;

	ret = quota_reserve_range(dst, &quota_res, pos_dst >> 9,
				  (pos_dst + aligned_len) >> 9);
	if (ret)
		goto err;

	file_update_time(file_dst);

	mark_pagecache_unallocated(src, pos_src >> 9,
				   (pos_src + aligned_len) >> 9);

	ret = bch2_remap_range(c,
			       inode_inum(dst), pos_dst >> 9,
			       inode_inum(src), pos_src >> 9,
			       aligned_len >> 9,
			       pos_dst + len, &i_sectors_delta);
	if (ret < 0)
		goto err;

	/*
	 * due to alignment, we might have remapped slightly more than requsted
	 */
	ret = min((u64) ret << 9, (u64) len);

	i_sectors_acct(c, dst, &quota_res, i_sectors_delta);

	spin_lock(&dst->v.i_lock);
	if (pos_dst + ret > dst->v.i_size)
		i_size_write(&dst->v, pos_dst + ret);
	spin_unlock(&dst->v.i_lock);

	if ((file_dst->f_flags & (__O_SYNC | O_DSYNC)) ||
	    IS_SYNC(file_inode(file_dst)))
		ret = bch2_flush_inode(c, inode_inum(dst));
err:
	bch2_quota_reservation_put(c, dst, &quota_res);
	bch2_unlock_inodes(INODE_LOCK|INODE_PAGECACHE_BLOCK, src, dst);

	return bch2_err_class(ret);
}

/* fseek: */

static int page_data_offset(struct page *page, unsigned offset)
{
	struct bch_page_state *s = bch2_page_state(page);
	unsigned i;

	if (s)
		for (i = offset >> 9; i < PAGE_SECTORS; i++)
			if (s->s[i].state >= SECTOR_DIRTY)
				return i << 9;

	return -1;
}

static loff_t bch2_seek_pagecache_data(struct inode *vinode,
				       loff_t start_offset,
				       loff_t end_offset)
{
	struct folio_batch fbatch;
	pgoff_t start_index	= start_offset >> PAGE_SHIFT;
	pgoff_t end_index	= end_offset >> PAGE_SHIFT;
	pgoff_t index		= start_index;
	unsigned i;
	loff_t ret;
	int offset;

	folio_batch_init(&fbatch);

	while (filemap_get_folios(vinode->i_mapping,
				  &index, end_index, &fbatch)) {
		for (i = 0; i < folio_batch_count(&fbatch); i++) {
			struct folio *folio = fbatch.folios[i];

			folio_lock(folio);

			offset = page_data_offset(&folio->page,
					folio->index == start_index
					? start_offset & (PAGE_SIZE - 1)
					: 0);
			if (offset >= 0) {
				ret = clamp(((loff_t) folio->index << PAGE_SHIFT) +
					    offset,
					    start_offset, end_offset);
				folio_unlock(folio);
				folio_batch_release(&fbatch);
				return ret;
			}

			folio_unlock(folio);
		}
		folio_batch_release(&fbatch);
		cond_resched();
	}

	return end_offset;
}

static loff_t bch2_seek_data(struct file *file, u64 offset)
{
	struct bch_inode_info *inode = file_bch_inode(file);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct btree_trans trans;
	struct btree_iter iter;
	struct bkey_s_c k;
	subvol_inum inum = inode_inum(inode);
	u64 isize, next_data = MAX_LFS_FILESIZE;
	u32 snapshot;
	int ret;

	isize = i_size_read(&inode->v);
	if (offset >= isize)
		return -ENXIO;

	bch2_trans_init(&trans, c, 0, 0);
retry:
	bch2_trans_begin(&trans);

	ret = bch2_subvolume_get_snapshot(&trans, inum.subvol, &snapshot);
	if (ret)
		goto err;

	for_each_btree_key_norestart(&trans, iter, BTREE_ID_extents,
			   SPOS(inode->v.i_ino, offset >> 9, snapshot), 0, k, ret) {
		if (k.k->p.inode != inode->v.i_ino) {
			break;
		} else if (bkey_extent_is_data(k.k)) {
			next_data = max(offset, bkey_start_offset(k.k) << 9);
			break;
		} else if (k.k->p.offset >> 9 > isize)
			break;
	}
	bch2_trans_iter_exit(&trans, &iter);
err:
	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
		goto retry;

	bch2_trans_exit(&trans);
	if (ret)
		return ret;

	if (next_data > offset)
		next_data = bch2_seek_pagecache_data(&inode->v,
						     offset, next_data);

	if (next_data >= isize)
		return -ENXIO;

	return vfs_setpos(file, next_data, MAX_LFS_FILESIZE);
}

static int __page_hole_offset(struct page *page, unsigned offset)
{
	struct bch_page_state *s = bch2_page_state(page);
	unsigned i;

	if (!s)
		return 0;

	for (i = offset >> 9; i < PAGE_SECTORS; i++)
		if (s->s[i].state < SECTOR_DIRTY)
			return i << 9;

	return -1;
}

static loff_t page_hole_offset(struct address_space *mapping, loff_t offset)
{
	pgoff_t index = offset >> PAGE_SHIFT;
	struct page *page;
	int pg_offset;
	loff_t ret = -1;

	page = find_lock_page(mapping, index);
	if (!page)
		return offset;

	pg_offset = __page_hole_offset(page, offset & (PAGE_SIZE - 1));
	if (pg_offset >= 0)
		ret = ((loff_t) index << PAGE_SHIFT) + pg_offset;

	unlock_page(page);

	return ret;
}

static loff_t bch2_seek_pagecache_hole(struct inode *vinode,
				       loff_t start_offset,
				       loff_t end_offset)
{
	struct address_space *mapping = vinode->i_mapping;
	loff_t offset = start_offset, hole;

	while (offset < end_offset) {
		hole = page_hole_offset(mapping, offset);
		if (hole >= 0 && hole <= end_offset)
			return max(start_offset, hole);

		offset += PAGE_SIZE;
		offset &= PAGE_MASK;
	}

	return end_offset;
}

static loff_t bch2_seek_hole(struct file *file, u64 offset)
{
	struct bch_inode_info *inode = file_bch_inode(file);
	struct bch_fs *c = inode->v.i_sb->s_fs_info;
	struct btree_trans trans;
	struct btree_iter iter;
	struct bkey_s_c k;
	subvol_inum inum = inode_inum(inode);
	u64 isize, next_hole = MAX_LFS_FILESIZE;
	u32 snapshot;
	int ret;

	isize = i_size_read(&inode->v);
	if (offset >= isize)
		return -ENXIO;

	bch2_trans_init(&trans, c, 0, 0);
retry:
	bch2_trans_begin(&trans);

	ret = bch2_subvolume_get_snapshot(&trans, inum.subvol, &snapshot);
	if (ret)
		goto err;

	for_each_btree_key_norestart(&trans, iter, BTREE_ID_extents,
			   SPOS(inode->v.i_ino, offset >> 9, snapshot),
			   BTREE_ITER_SLOTS, k, ret) {
		if (k.k->p.inode != inode->v.i_ino) {
			next_hole = bch2_seek_pagecache_hole(&inode->v,
					offset, MAX_LFS_FILESIZE);
			break;
		} else if (!bkey_extent_is_data(k.k)) {
			next_hole = bch2_seek_pagecache_hole(&inode->v,
					max(offset, bkey_start_offset(k.k) << 9),
					k.k->p.offset << 9);

			if (next_hole < k.k->p.offset << 9)
				break;
		} else {
			offset = max(offset, bkey_start_offset(k.k) << 9);
		}
	}
	bch2_trans_iter_exit(&trans, &iter);
err:
	if (bch2_err_matches(ret, BCH_ERR_transaction_restart))
		goto retry;

	bch2_trans_exit(&trans);
	if (ret)
		return ret;

	if (next_hole > isize)
		next_hole = isize;

	return vfs_setpos(file, next_hole, MAX_LFS_FILESIZE);
}

loff_t bch2_llseek(struct file *file, loff_t offset, int whence)
{
	loff_t ret;

	switch (whence) {
	case SEEK_SET:
	case SEEK_CUR:
	case SEEK_END:
		ret = generic_file_llseek(file, offset, whence);
		break;
	case SEEK_DATA:
		ret = bch2_seek_data(file, offset);
		break;
	case SEEK_HOLE:
		ret = bch2_seek_hole(file, offset);
		break;
	default:
		ret = -EINVAL;
		break;
	}

	return bch2_err_class(ret);
}

void bch2_fs_fsio_exit(struct bch_fs *c)
{
	bioset_exit(&c->dio_write_bioset);
	bioset_exit(&c->dio_read_bioset);
	bioset_exit(&c->writepage_bioset);
}

int bch2_fs_fsio_init(struct bch_fs *c)
{
	int ret = 0;

	pr_verbose_init(c->opts, "");

	if (bioset_init(&c->writepage_bioset,
			4, offsetof(struct bch_writepage_io, op.wbio.bio),
			BIOSET_NEED_BVECS) ||
	    bioset_init(&c->dio_read_bioset,
			4, offsetof(struct dio_read, rbio.bio),
			BIOSET_NEED_BVECS) ||
	    bioset_init(&c->dio_write_bioset,
			4, offsetof(struct dio_write, op.wbio.bio),
			BIOSET_NEED_BVECS))
		ret = -ENOMEM;

	pr_verbose_init(c->opts, "ret %i", ret);
	return ret;
}

#endif /* NO_BCACHEFS_FS */