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-rw-r--r--fs/netfs/buffered_read.c428
1 files changed, 428 insertions, 0 deletions
diff --git a/fs/netfs/buffered_read.c b/fs/netfs/buffered_read.c
new file mode 100644
index 000000000000..281a88a5b8dc
--- /dev/null
+++ b/fs/netfs/buffered_read.c
@@ -0,0 +1,428 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* Network filesystem high-level buffered read support.
+ *
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/export.h>
+#include <linux/task_io_accounting_ops.h>
+#include "internal.h"
+
+/*
+ * Unlock the folios in a read operation. We need to set PG_fscache on any
+ * folios we're going to write back before we unlock them.
+ */
+void netfs_rreq_unlock_folios(struct netfs_io_request *rreq)
+{
+ struct netfs_io_subrequest *subreq;
+ struct folio *folio;
+ unsigned int iopos, account = 0;
+ pgoff_t start_page = rreq->start / PAGE_SIZE;
+ pgoff_t last_page = ((rreq->start + rreq->len) / PAGE_SIZE) - 1;
+ bool subreq_failed = false;
+
+ XA_STATE(xas, &rreq->mapping->i_pages, start_page);
+
+ if (test_bit(NETFS_RREQ_FAILED, &rreq->flags)) {
+ __clear_bit(NETFS_RREQ_COPY_TO_CACHE, &rreq->flags);
+ list_for_each_entry(subreq, &rreq->subrequests, rreq_link) {
+ __clear_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags);
+ }
+ }
+
+ /* Walk through the pagecache and the I/O request lists simultaneously.
+ * We may have a mixture of cached and uncached sections and we only
+ * really want to write out the uncached sections. This is slightly
+ * complicated by the possibility that we might have huge pages with a
+ * mixture inside.
+ */
+ subreq = list_first_entry(&rreq->subrequests,
+ struct netfs_io_subrequest, rreq_link);
+ iopos = 0;
+ subreq_failed = (subreq->error < 0);
+
+ trace_netfs_rreq(rreq, netfs_rreq_trace_unlock);
+
+ rcu_read_lock();
+ xas_for_each(&xas, folio, last_page) {
+ unsigned int pgpos = (folio_index(folio) - start_page) * PAGE_SIZE;
+ unsigned int pgend = pgpos + folio_size(folio);
+ bool pg_failed = false;
+
+ for (;;) {
+ if (!subreq) {
+ pg_failed = true;
+ break;
+ }
+ if (test_bit(NETFS_SREQ_COPY_TO_CACHE, &subreq->flags))
+ folio_start_fscache(folio);
+ pg_failed |= subreq_failed;
+ if (pgend < iopos + subreq->len)
+ break;
+
+ account += subreq->transferred;
+ iopos += subreq->len;
+ if (!list_is_last(&subreq->rreq_link, &rreq->subrequests)) {
+ subreq = list_next_entry(subreq, rreq_link);
+ subreq_failed = (subreq->error < 0);
+ } else {
+ subreq = NULL;
+ subreq_failed = false;
+ }
+ if (pgend == iopos)
+ break;
+ }
+
+ if (!pg_failed) {
+ flush_dcache_folio(folio);
+ folio_mark_uptodate(folio);
+ }
+
+ if (!test_bit(NETFS_RREQ_DONT_UNLOCK_FOLIOS, &rreq->flags)) {
+ if (folio_index(folio) == rreq->no_unlock_folio &&
+ test_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags))
+ _debug("no unlock");
+ else
+ folio_unlock(folio);
+ }
+ }
+ rcu_read_unlock();
+
+ task_io_account_read(account);
+ if (rreq->netfs_ops->done)
+ rreq->netfs_ops->done(rreq);
+}
+
+static void netfs_cache_expand_readahead(struct netfs_io_request *rreq,
+ loff_t *_start, size_t *_len, loff_t i_size)
+{
+ struct netfs_cache_resources *cres = &rreq->cache_resources;
+
+ if (cres->ops && cres->ops->expand_readahead)
+ cres->ops->expand_readahead(cres, _start, _len, i_size);
+}
+
+static void netfs_rreq_expand(struct netfs_io_request *rreq,
+ struct readahead_control *ractl)
+{
+ /* Give the cache a chance to change the request parameters. The
+ * resultant request must contain the original region.
+ */
+ netfs_cache_expand_readahead(rreq, &rreq->start, &rreq->len, rreq->i_size);
+
+ /* Give the netfs a chance to change the request parameters. The
+ * resultant request must contain the original region.
+ */
+ if (rreq->netfs_ops->expand_readahead)
+ rreq->netfs_ops->expand_readahead(rreq);
+
+ /* Expand the request if the cache wants it to start earlier. Note
+ * that the expansion may get further extended if the VM wishes to
+ * insert THPs and the preferred start and/or end wind up in the middle
+ * of THPs.
+ *
+ * If this is the case, however, the THP size should be an integer
+ * multiple of the cache granule size, so we get a whole number of
+ * granules to deal with.
+ */
+ if (rreq->start != readahead_pos(ractl) ||
+ rreq->len != readahead_length(ractl)) {
+ readahead_expand(ractl, rreq->start, rreq->len);
+ rreq->start = readahead_pos(ractl);
+ rreq->len = readahead_length(ractl);
+
+ trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+ netfs_read_trace_expanded);
+ }
+}
+
+/**
+ * netfs_readahead - Helper to manage a read request
+ * @ractl: The description of the readahead request
+ *
+ * Fulfil a readahead request by drawing data from the cache if possible, or
+ * the netfs if not. Space beyond the EOF is zero-filled. Multiple I/O
+ * requests from different sources will get munged together. If necessary, the
+ * readahead window can be expanded in either direction to a more convenient
+ * alighment for RPC efficiency or to make storage in the cache feasible.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+void netfs_readahead(struct readahead_control *ractl)
+{
+ struct netfs_io_request *rreq;
+ struct netfs_i_context *ctx = netfs_i_context(ractl->mapping->host);
+ int ret;
+
+ _enter("%lx,%x", readahead_index(ractl), readahead_count(ractl));
+
+ if (readahead_count(ractl) == 0)
+ return;
+
+ rreq = netfs_alloc_request(ractl->mapping, ractl->file,
+ readahead_pos(ractl),
+ readahead_length(ractl),
+ NETFS_READAHEAD);
+ if (IS_ERR(rreq))
+ return;
+
+ if (ctx->ops->begin_cache_operation) {
+ ret = ctx->ops->begin_cache_operation(rreq);
+ if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+ goto cleanup_free;
+ }
+
+ netfs_stat(&netfs_n_rh_readahead);
+ trace_netfs_read(rreq, readahead_pos(ractl), readahead_length(ractl),
+ netfs_read_trace_readahead);
+
+ netfs_rreq_expand(rreq, ractl);
+
+ /* Drop the refs on the folios here rather than in the cache or
+ * filesystem. The locks will be dropped in netfs_rreq_unlock().
+ */
+ while (readahead_folio(ractl))
+ ;
+
+ netfs_begin_read(rreq, false);
+ return;
+
+cleanup_free:
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
+ return;
+}
+EXPORT_SYMBOL(netfs_readahead);
+
+/**
+ * netfs_readpage - Helper to manage a readpage request
+ * @file: The file to read from
+ * @subpage: A subpage of the folio to read
+ *
+ * Fulfil a readpage request by drawing data from the cache if possible, or the
+ * netfs if not. Space beyond the EOF is zero-filled. Multiple I/O requests
+ * from different sources will get munged together.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+int netfs_readpage(struct file *file, struct page *subpage)
+{
+ struct folio *folio = page_folio(subpage);
+ struct address_space *mapping = folio_file_mapping(folio);
+ struct netfs_io_request *rreq;
+ struct netfs_i_context *ctx = netfs_i_context(mapping->host);
+ int ret;
+
+ _enter("%lx", folio_index(folio));
+
+ rreq = netfs_alloc_request(mapping, file,
+ folio_file_pos(folio), folio_size(folio),
+ NETFS_READPAGE);
+ if (IS_ERR(rreq)) {
+ ret = PTR_ERR(rreq);
+ goto alloc_error;
+ }
+
+ if (ctx->ops->begin_cache_operation) {
+ ret = ctx->ops->begin_cache_operation(rreq);
+ if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+ goto discard;
+ }
+
+ netfs_stat(&netfs_n_rh_readpage);
+ trace_netfs_read(rreq, rreq->start, rreq->len, netfs_read_trace_readpage);
+ return netfs_begin_read(rreq, true);
+
+discard:
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_discard);
+alloc_error:
+ folio_unlock(folio);
+ return ret;
+}
+EXPORT_SYMBOL(netfs_readpage);
+
+/*
+ * Prepare a folio for writing without reading first
+ * @folio: The folio being prepared
+ * @pos: starting position for the write
+ * @len: length of write
+ * @always_fill: T if the folio should always be completely filled/cleared
+ *
+ * In some cases, write_begin doesn't need to read at all:
+ * - full folio write
+ * - write that lies in a folio that is completely beyond EOF
+ * - write that covers the folio from start to EOF or beyond it
+ *
+ * If any of these criteria are met, then zero out the unwritten parts
+ * of the folio and return true. Otherwise, return false.
+ */
+static bool netfs_skip_folio_read(struct folio *folio, loff_t pos, size_t len,
+ bool always_fill)
+{
+ struct inode *inode = folio_inode(folio);
+ loff_t i_size = i_size_read(inode);
+ size_t offset = offset_in_folio(folio, pos);
+ size_t plen = folio_size(folio);
+
+ if (unlikely(always_fill)) {
+ if (pos - offset + len <= i_size)
+ return false; /* Page entirely before EOF */
+ zero_user_segment(&folio->page, 0, plen);
+ folio_mark_uptodate(folio);
+ return true;
+ }
+
+ /* Full folio write */
+ if (offset == 0 && len >= plen)
+ return true;
+
+ /* Page entirely beyond the end of the file */
+ if (pos - offset >= i_size)
+ goto zero_out;
+
+ /* Write that covers from the start of the folio to EOF or beyond */
+ if (offset == 0 && (pos + len) >= i_size)
+ goto zero_out;
+
+ return false;
+zero_out:
+ zero_user_segments(&folio->page, 0, offset, offset + len, plen);
+ return true;
+}
+
+/**
+ * netfs_write_begin - Helper to prepare for writing
+ * @file: The file to read from
+ * @mapping: The mapping to read from
+ * @pos: File position at which the write will begin
+ * @len: The length of the write (may extend beyond the end of the folio chosen)
+ * @aop_flags: AOP_* flags
+ * @_folio: Where to put the resultant folio
+ * @_fsdata: Place for the netfs to store a cookie
+ *
+ * Pre-read data for a write-begin request by drawing data from the cache if
+ * possible, or the netfs if not. Space beyond the EOF is zero-filled.
+ * Multiple I/O requests from different sources will get munged together. If
+ * necessary, the readahead window can be expanded in either direction to a
+ * more convenient alighment for RPC efficiency or to make storage in the cache
+ * feasible.
+ *
+ * The calling netfs must provide a table of operations, only one of which,
+ * issue_op, is mandatory.
+ *
+ * The check_write_begin() operation can be provided to check for and flush
+ * conflicting writes once the folio is grabbed and locked. It is passed a
+ * pointer to the fsdata cookie that gets returned to the VM to be passed to
+ * write_end. It is permitted to sleep. It should return 0 if the request
+ * should go ahead; unlock the folio and return -EAGAIN to cause the folio to
+ * be regot; or return an error.
+ *
+ * The calling netfs must initialise a netfs context contiguous to the vfs
+ * inode before calling this.
+ *
+ * This is usable whether or not caching is enabled.
+ */
+int netfs_write_begin(struct file *file, struct address_space *mapping,
+ loff_t pos, unsigned int len, unsigned int aop_flags,
+ struct folio **_folio, void **_fsdata)
+{
+ struct netfs_io_request *rreq;
+ struct netfs_i_context *ctx = netfs_i_context(file_inode(file ));
+ struct folio *folio;
+ unsigned int fgp_flags;
+ pgoff_t index = pos >> PAGE_SHIFT;
+ int ret;
+
+ DEFINE_READAHEAD(ractl, file, NULL, mapping, index);
+
+retry:
+ fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
+ if (aop_flags & AOP_FLAG_NOFS)
+ fgp_flags |= FGP_NOFS;
+ folio = __filemap_get_folio(mapping, index, fgp_flags,
+ mapping_gfp_mask(mapping));
+ if (!folio)
+ return -ENOMEM;
+
+ if (ctx->ops->check_write_begin) {
+ /* Allow the netfs (eg. ceph) to flush conflicts. */
+ ret = ctx->ops->check_write_begin(file, pos, len, folio, _fsdata);
+ if (ret < 0) {
+ trace_netfs_failure(NULL, NULL, ret, netfs_fail_check_write_begin);
+ if (ret == -EAGAIN)
+ goto retry;
+ goto error;
+ }
+ }
+
+ if (folio_test_uptodate(folio))
+ goto have_folio;
+
+ /* If the page is beyond the EOF, we want to clear it - unless it's
+ * within the cache granule containing the EOF, in which case we need
+ * to preload the granule.
+ */
+ if (!netfs_is_cache_enabled(ctx) &&
+ netfs_skip_folio_read(folio, pos, len, false)) {
+ netfs_stat(&netfs_n_rh_write_zskip);
+ goto have_folio_no_wait;
+ }
+
+ rreq = netfs_alloc_request(mapping, file,
+ folio_file_pos(folio), folio_size(folio),
+ NETFS_READ_FOR_WRITE);
+ if (IS_ERR(rreq)) {
+ ret = PTR_ERR(rreq);
+ goto error;
+ }
+ rreq->no_unlock_folio = folio_index(folio);
+ __set_bit(NETFS_RREQ_NO_UNLOCK_FOLIO, &rreq->flags);
+
+ if (ctx->ops->begin_cache_operation) {
+ ret = ctx->ops->begin_cache_operation(rreq);
+ if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
+ goto error_put;
+ }
+
+ netfs_stat(&netfs_n_rh_write_begin);
+ trace_netfs_read(rreq, pos, len, netfs_read_trace_write_begin);
+
+ /* Expand the request to meet caching requirements and download
+ * preferences.
+ */
+ ractl._nr_pages = folio_nr_pages(folio);
+ netfs_rreq_expand(rreq, &ractl);
+
+ /* We hold the folio locks, so we can drop the references */
+ folio_get(folio);
+ while (readahead_folio(&ractl))
+ ;
+
+ ret = netfs_begin_read(rreq, true);
+ if (ret < 0)
+ goto error;
+
+have_folio:
+ ret = folio_wait_fscache_killable(folio);
+ if (ret < 0)
+ goto error;
+have_folio_no_wait:
+ *_folio = folio;
+ _leave(" = 0");
+ return 0;
+
+error_put:
+ netfs_put_request(rreq, false, netfs_rreq_trace_put_failed);
+error:
+ folio_unlock(folio);
+ folio_put(folio);
+ _leave(" = %d", ret);
+ return ret;
+}
+EXPORT_SYMBOL(netfs_write_begin);