Btrfs: add and improve comments

This improves the comments at the top of many functions.  It didn't
dive into the guts of functions because I was trying to
avoid merging problems with the new allocator and back reference work.

extent-tree.c and volumes.c were both skipped, and there is definitely
more work todo in cleaning and commenting the code.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

1 files changed, 51 insertions, 3 deletions

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index 0577fda2168a..0b2e623cf421 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -25,27 +25,58 @@
 
 /* in memory btrfs inode */
 struct btrfs_inode {
+	/* which subvolume this inode belongs to */
 	struct btrfs_root *root;
+
+	/* the block group preferred for allocations.  This pointer is buggy
+	 * and needs to be replaced with a bytenr instead
+	 */
 	struct btrfs_block_group_cache *block_group;
+
+	/* key used to find this inode on disk.  This is used by the code
+	 * to read in roots of subvolumes
+	 */
 	struct btrfs_key location;
+
+	/* the extent_tree has caches of all the extent mappings to disk */
 	struct extent_map_tree extent_tree;
+
+	/* the io_tree does range state (DIRTY, LOCKED etc) */
 	struct extent_io_tree io_tree;
+
+	/* special utility tree used to record which mirrors have already been
+	 * tried when checksums fail for a given block
+	 */
 	struct extent_io_tree io_failure_tree;
+
+	/* held while inserting checksums to avoid races */
 	struct mutex csum_mutex;
+
+	/* held while inesrting or deleting extents from files */
 	struct mutex extent_mutex;
+
+	/* held while logging the inode in tree-log.c */
 	struct mutex log_mutex;
-	struct inode vfs_inode;
+
+	/* used to order data wrt metadata */
 	struct btrfs_ordered_inode_tree ordered_tree;
 
+	/* standard acl pointers */
 	struct posix_acl *i_acl;
 	struct posix_acl *i_default_acl;
 
 	/* for keeping track of orphaned inodes */
 	struct list_head i_orphan;
 
+	/* list of all the delalloc inodes in the FS.  There are times we need
+	 * to write all the delalloc pages to disk, and this list is used
+	 * to walk them all.
+	 */
 	struct list_head delalloc_inodes;
 
-	/* full 64 bit generation number */
+	/* full 64 bit generation number, struct vfs_inode doesn't have a big
+	 * enough field for this.
+	 */
 	u64 generation;
 
 	/*
@@ -57,10 +88,25 @@ struct btrfs_inode {
 	 */
 	u64 logged_trans;
 
-	/* trans that last made a change that should be fully fsync'd */
+	/*
+	 * trans that last made a change that should be fully fsync'd.  This
+	 * gets reset to zero each time the inode is logged
+	 */
 	u64 log_dirty_trans;
+
+	/* total number of bytes pending delalloc, used by stat to calc the
+	 * real block usage of the file
+	 */
 	u64 delalloc_bytes;
+
+	/*
+	 * the size of the file stored in the metadata on disk.  data=ordered
+	 * means the in-memory i_size might be larger than the size on disk
+	 * because not all the blocks are written yet.
+	 */
 	u64 disk_i_size;
+
+	/* flags field from the on disk inode */
 	u32 flags;
 
 	/*
@@ -68,6 +114,8 @@ struct btrfs_inode {
 	 * number for new files that are created
 	 */
 	u64 index_cnt;
+
+	struct inode vfs_inode;
 };
 
 static inline struct btrfs_inode *BTRFS_I(struct inode *inode)