On 18/06/2020 09:50, Qu Wenruo wrote:
> These two functions have extra conditions that their callers need to
> meet, and some not-that-common parameters used for return value.
>
> So adding some comments may save reviewers some time.
These comments have a style/formatting similar to kerneldoc, can you make
them real kerneldoc?
>
> Signed-off-by: Qu Wenruo <wqu@xxxxxxxx>
> ---
> fs/btrfs/file.c | 19 +++++++++++++++++++
> fs/btrfs/inode.c | 19 +++++++++++++++++--
> 2 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index fccf5862cd3e..0e4f57fb2737 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1533,6 +1533,25 @@ lock_and_cleanup_extent_if_need(struct btrfs_inode *inode, struct page **pages,
> return ret;
> }
>
> +/*
> + * Check if we can do nocow write into the range [@pos, @pos + @write_bytes)
> + *
> + * This function will flush ordered extents in the range to ensure proper
> + * nocow checks for (nowait == false) case.
> + *
> + * Return >0 and update @write_bytes if we can do nocow write into the range.
> + * Return 0 if we can't do nocow write.
> + * Return -EAGAIN if we can't get the needed lock, or for (nowait == true) case,
> + * there are ordered extents need to be flushed.
> + * Return <0 for if other error happened.
> + *
> + * NOTE: For wait (nowait==false) calls, callers need to release the drew write
> + * lock of inode->root->snapshot_lock if return value > 0.
> + *
> + * @pos: File offset of the range
> + * @write_bytes: The length of the range to check, also contains the nocow
> + * writable length if we can do nocow write
> + */
> static noinline int check_can_nocow(struct btrfs_inode *inode, loff_t pos,
> size_t *write_bytes, bool nowait)
> {
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 86f7aa377da9..48e16eae7278 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -6922,8 +6922,23 @@ static struct extent_map *btrfs_new_extent_direct(struct inode *inode,
> }
>
> /*
> - * returns 1 when the nocow is safe, < 1 on error, 0 if the
> - * block must be cow'd
> + * Check if we can write into [@offset, @offset + @len) of @inode.
> + *
> + * Return >0 and update @len if we can do nocow write into [@offset, @offset +
> + * @len).
> + * Return 0 if we can't do nocow write.
> + * Return <0 if error happened.
> + *
> + * NOTE: This only checks the file extents, caller is responsible to wait for
> + * any ordered extents.
> + *
> + * @offset: File offset
> + * @len: The length to write, will be updated to the nocow writable
> + * range
> + *
> + * @orig_start: (Optional) Return the original file offset of the file extent
> + * @orig_len: (Optional) Return the original on-disk length of the file extent
> + * @ram_bytes: (Optional) Return the ram_bytes of the file extent
> */
> noinline int can_nocow_extent(struct inode *inode, u64 offset, u64 *len,
> u64 *orig_start, u64 *orig_block_len,
>
