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btrfs: improve comments around nocow path

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run_delalloc_nocow contains numerous, somewhat subtle, checks when
figuring out whether a particular extent should be CoW'ed or not. This
patch explicitly states the assumptions those checks verify. As a
result also document 2 of the more subtle checks in check_committed_ref
as well.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Nikolay Borisov
2019-08-21 10:42:57 +03:00
committed by David Sterba
parent 3e024846d2
commit a6bd9cd155
2 changed files with 50 additions and 4 deletions
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3
fs/btrfs/extent-tree.c
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@@ -2357,16 +2357,19 @@ static noinline int check_committed_ref(struct btrfs_root *root,
item_size = btrfs_item_size_nr(leaf, path->slots[0]);
ei = btrfs_item_ptr(leaf, path->slots[0], struct btrfs_extent_item);
/* If extent item has more than 1 inline ref then it's shared */
if (item_size != sizeof(*ei) +
btrfs_extent_inline_ref_size(BTRFS_EXTENT_DATA_REF_KEY))
goto out;
/* If extent created before last snapshot => it's definitely shared */
if (btrfs_extent_generation(leaf, ei) <=
btrfs_root_last_snapshot(&root->root_item))
goto out;
iref = (struct btrfs_extent_inline_ref *)(ei + 1);
/* If this extent has SHARED_DATA_REF then it's shared */
type = btrfs_get_extent_inline_ref_type(leaf, iref, BTRFS_REF_TYPE_DATA);
if (type != BTRFS_EXTENT_DATA_REF_KEY)
goto out;