btrfs: rework the order of btrfs_ordered_extent::flags

[BUG]
There is a long existing bug in the last parameter of
btrfs_add_ordered_extent(), in commit 771ed689d2cd ("Btrfs: Optimize
compressed writeback and reads") back to 2008.

In that ancient commit btrfs_add_ordered_extent() expects the @type
parameter to be one of the following:

- BTRFS_ORDERED_REGULAR
- BTRFS_ORDERED_NOCOW
- BTRFS_ORDERED_PREALLOC
- BTRFS_ORDERED_COMPRESSED

But we pass 0 in cow_file_range(), which means BTRFS_ORDERED_IO_DONE.

Ironically extra check in __btrfs_add_ordered_extent() won't set the bit
if we see (type == IO_DONE || type == IO_COMPLETE), and avoid any
obvious bug.

But this still leads to regular COW ordered extent having no bit to
indicate its type in various trace events, rendering REGULAR bit
useless.

[FIX]
Change the following aspects to avoid such problem:

- Reorder btrfs_ordered_extent::flags
  Now the type bits go first (REGULAR/NOCOW/PREALLCO/COMPRESSED), then
  DIRECT bit, finally extra status bits like IO_DONE/COMPLETE/IOERR.

- Add extra ASSERT() for btrfs_add_ordered_extent_*()

- Remove @type parameter for btrfs_add_ordered_extent_compress()
  As the only valid @type here is BTRFS_ORDERED_COMPRESSED.

- Remove the unnecessary special check for IO_DONE/COMPLETE in
  __btrfs_add_ordered_extent()
  This is just to make the code work, with extra ASSERT(), there are
  limited values can be passed in.

Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 24 insertions, 13 deletions

diff --git a/fs/btrfs/ordered-data.h b/fs/btrfs/ordered-data.h
index 46194c2c05d4..cca3307807e8 100644
--- a/fs/btrfs/ordered-data.h
+++ b/fs/btrfs/ordered-data.h
@@ -27,7 +27,7 @@ struct btrfs_ordered_sum {
 };
 
 /*
- * bits for the flags field:
+ * Bits for btrfs_ordered_extent::flags.
  *
  * BTRFS_ORDERED_IO_DONE is set when all of the blocks are written.
  * It is used to make sure metadata is inserted into the tree only once
@@ -38,24 +38,36 @@ struct btrfs_ordered_sum {
  * IO is done and any metadata is inserted into the tree.
  */
 enum {
+	/*
+	 * Different types for direct io, one and only one of the 4 type can
+	 * be set when creating ordered extent.
+	 *
+	 * REGULAR:	For regular non-compressed COW write
+	 * NOCOW:	For NOCOW write into existing non-hole extent
+	 * PREALLOC:	For NOCOW write into preallocated extent
+	 * COMPRESSED:	For compressed COW write
+	 */
+	BTRFS_ORDERED_REGULAR,
+	BTRFS_ORDERED_NOCOW,
+	BTRFS_ORDERED_PREALLOC,
+	BTRFS_ORDERED_COMPRESSED,
+
+	/*
+	 * Extra bit for direct io, can only be set for
+	 * REGULAR/NOCOW/PREALLOC. No direct io for compressed extent.
+	 */
+	BTRFS_ORDERED_DIRECT,
+
+	/* Extra status bits for ordered extents */
+
 	/* set when all the pages are written */
 	BTRFS_ORDERED_IO_DONE,
 	/* set when removed from the tree */
 	BTRFS_ORDERED_COMPLETE,
-	/* set when we want to write in place */
-	BTRFS_ORDERED_NOCOW,
-	/* writing a zlib compressed extent */
-	BTRFS_ORDERED_COMPRESSED,
-	/* set when writing to preallocated extent */
-	BTRFS_ORDERED_PREALLOC,
-	/* set when we're doing DIO with this extent */
-	BTRFS_ORDERED_DIRECT,
 	/* We had an io error when writing this out */
 	BTRFS_ORDERED_IOERR,
 	/* Set when we have to truncate an extent */
 	BTRFS_ORDERED_TRUNCATED,
-	/* Regular IO for COW */
-	BTRFS_ORDERED_REGULAR,
 	/* Used during fsync to track already logged extents */
 	BTRFS_ORDERED_LOGGED,
 	/* We have already logged all the csums of the ordered extent */
@@ -167,8 +179,7 @@ int btrfs_add_ordered_extent_dio(struct btrfs_inode *inode, u64 file_offset,
 				 u64 disk_num_bytes, int type);
 int btrfs_add_ordered_extent_compress(struct btrfs_inode *inode, u64 file_offset,
 				      u64 disk_bytenr, u64 num_bytes,
-				      u64 disk_num_bytes, int type,
-				      int compress_type);
+				      u64 disk_num_bytes, int compress_type);
 void btrfs_add_ordered_sum(struct btrfs_ordered_extent *entry,
 			   struct btrfs_ordered_sum *sum);
 struct btrfs_ordered_extent *btrfs_lookup_ordered_extent(struct btrfs_inode *inode,