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Btrfs: add and improve comments

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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>
This commit is contained in:
Chris Mason
2008-09-29 15:18:18 -04:00
parent 9a5e1ea1e1
commit d352ac6814
25 changed files with 653 additions and 277 deletions
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33
fs/btrfs/disk-io.c
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@@ -55,6 +55,11 @@ static int check_tree_block(struct btrfs_root *root, struct extent_buffer *buf)
static struct extent_io_ops btree_extent_io_ops;
static void end_workqueue_fn(struct btrfs_work *work);
/*
* end_io_wq structs are used to do processing in task context when an IO is
* complete. This is used during reads to verify checksums, and it is used
* by writes to insert metadata for new file extents after IO is complete.
*/
struct end_io_wq {
struct bio *bio;
bio_end_io_t *end_io;
@@ -66,6 +71,11 @@ struct end_io_wq {
struct btrfs_work work;
};
/*
* async submit bios are used to offload expensive checksumming
* onto the worker threads. They checksum file and metadata bios
* just before they are sent down the IO stack.
*/
struct async_submit_bio {
struct inode *inode;
struct bio *bio;
@@ -76,6 +86,10 @@ struct async_submit_bio {
struct btrfs_work work;
};
/*
* extents on the btree inode are pretty simple, there's one extent
* that covers the entire device
*/
struct extent_map *btree_get_extent(struct inode *inode, struct page *page,
size_t page_offset, u64 start, u64 len,
int create)
@@ -151,6 +165,10 @@ void btrfs_csum_final(u32 crc, char *result)
*(__le32 *)result = ~cpu_to_le32(crc);
}
/*
* compute the csum for a btree block, and either verify it or write it
* into the csum field of the block.
*/
static int csum_tree_block(struct btrfs_root *root, struct extent_buffer *buf,
int verify)
{
@@ -204,6 +222,12 @@ static int csum_tree_block(struct btrfs_root *root, struct extent_buffer *buf,
return 0;
}
/*
* we can't consider a given block up to date unless the transid of the
* block matches the transid in the parent node's pointer. This is how we
* detect blocks that either didn't get written at all or got written
* in the wrong place.
*/
static int verify_parent_transid(struct extent_io_tree *io_tree,
struct extent_buffer *eb, u64 parent_transid)
{
@@ -228,9 +252,12 @@ out:
unlock_extent(io_tree, eb->start, eb->start + eb->len - 1,
GFP_NOFS);
return ret;
}
/*
* helper to read a given tree block, doing retries as required when
* the checksums don't match and we have alternate mirrors to try.
*/
static int btree_read_extent_buffer_pages(struct btrfs_root *root,
struct extent_buffer *eb,
u64 start, u64 parent_transid)
@@ -260,6 +287,10 @@ printk("read extent buffer pages failed with ret %d mirror no %d\n", ret, mirror
return -EIO;
}
/*
* checksum a dirty tree block before IO. This has extra checks to make
* sure we only fill in the checksum field in the first page of a multi-page block
*/
int csum_dirty_buffer(struct btrfs_root *root, struct page *page)
{
struct extent_io_tree *tree;