btrfs: better document struct btrfs_bio

Update the comments on btrfs_bio to better describe the structure.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/bio.h b/fs/btrfs/bio.h
index b12f84b3b3410f0479fd176c124a9bc55acce6e3..baaa27961cc8121363759567c69bdda0e440c5a3 100644 (file)
--- a/fs/btrfs/bio.h
+++ b/fs/btrfs/bio.h
@@ -26,9 +26,8 @@ struct btrfs_fs_info;
 typedef void (*btrfs_bio_end_io_t)(struct btrfs_bio *bbio);
 
 /*
- * Additional info to pass along bio.
- *
- * Mostly for btrfs specific features like csum and mirror_num.
+ * Highlevel btrfs I/O structure.  It is allocated by btrfs_bio_alloc and
+ * passed to btrfs_submit_bio for mapping to the physical devices.
  */
 struct btrfs_bio {
        unsigned int mirror_num:7;
@@ -42,7 +41,7 @@ struct btrfs_bio {
        unsigned int is_metadata:1;
        struct bvec_iter iter;
 
-       /* for direct I/O */
+       /* File offset that this I/O operates on. */
        u64 file_offset;
 
        /* @device is for stripe IO submission. */
@@ -62,7 +61,7 @@ struct btrfs_bio {
        btrfs_bio_end_io_t end_io;
        void *private;
 
-       /* For read end I/O handling */
+       /* For internal use in read end I/O handling */
        struct work_struct end_io_work;
 
        /*