bcachefs: Nocow support

This adds support for nocow mode, where we do writes in-place when
possible. Patch components:

 - New boolean filesystem and inode option, nocow: note that when nocow
   is enabled, data checksumming and compression are implicitly disabled

 - To prevent in-place writes from racing with data moves
   (data_update.c) or bucket reuse (i.e. a bucket being reused and
   re-allocated while a nocow write is in flight, we have a new locking
   mechanism.

   Buckets can be locked for either data update or data move, using a
   fixed size hash table of two_state_shared locks. We don't have any
   chaining, meaning updates and moves to different buckets that hash to
   the same lock will wait unnecessarily - we'll want to watch for this
   becoming an issue.

 - The allocator path also needs to check for in-place writes in flight
   to a given bucket before giving it out: thus we add another counter
   to bucket_alloc_state so we can track this.

 - Fsync now may need to issue cache flushes to block devices instead of
   flushing the journal. We add a device bitmask to bch_inode_info,
   ei_devs_need_flush, which tracks devices that need to have flushes
   issued - note that this will lead to unnecessary flushes when other
   codepaths have already issued flushes, we may want to replace this with
   a sequence number.

 - New nocow write path: look up extents, and if they're writable write
   to them - otherwise fall back to the normal COW write path.

XXX: switch to sequence numbers instead of bitmask for devs needing
journal flush

XXX: ei_quota_lock being a mutex means bch2_nocow_write_done() needs to
run in process context - see if we can improve this

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 5 insertions, 2 deletions

diff --git a/fs/bcachefs/checksum.h b/fs/bcachefs/checksum.h
index f7ccef7a5520..409ad534d9f4 100644
--- a/fs/bcachefs/checksum.h
+++ b/fs/bcachefs/checksum.h
@@ -99,14 +99,17 @@ static inline enum bch_csum_type bch2_csum_opt_to_type(enum bch_csum_opts type,
 }
 
 static inline enum bch_csum_type bch2_data_checksum_type(struct bch_fs *c,
-							 unsigned opt)
+							 struct bch_io_opts opts)
 {
+	if (opts.nocow)
+		return 0;
+
 	if (c->sb.encryption_type)
 		return c->opts.wide_macs
 			? BCH_CSUM_chacha20_poly1305_128
 			: BCH_CSUM_chacha20_poly1305_80;
 
-	return bch2_csum_opt_to_type(opt, true);
+	return bch2_csum_opt_to_type(opts.data_checksum, true);
 }
 
 static inline enum bch_csum_type bch2_meta_checksum_type(struct bch_fs *c)