Re: [PATCH U-BOOT 3/3] btrfs: btfs_file_read: zero trailing data if no extent was found

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2023/4/18 09:17, Dominique Martinet wrote:
> From: Dominique Martinet <dominique.martinet@atmark-techno.com>
> 
> btfs_file_read's truncate path has a comment noting '>0 means no extent'
> and bailing out immediately, but the buffer has not been written so
> probably needs zeroing out.
> 
> This is a theorical fix only and hasn't been tested on a file that
> actually runs this code path.

IIRC there is a memset() at the very beginning of btrfs_file_read() to 
set the whole dest memory to zero.

This is to handle cases like NO_HOLE cases, which we can skip hole extents.

Thanks,
Qu
> 
> Signed-off-by: Dominique Martinet <dominique.martinet@atmark-techno.com>
> ---
>   fs/btrfs/inode.c | 7 +++++--
>   1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index efffec0f2e68..23c006c98c3b 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -756,9 +756,12 @@ int btrfs_file_read(struct btrfs_root *root, u64 ino, u64 file_offset, u64 len,
>   		btrfs_release_path(&path);
>   		ret = lookup_data_extent(root, &path, ino, cur,
>   					 &next_offset);
> -		/* <0 is error, >0 means no extent */
> -		if (ret)
> +		/* <0 is error, >0 means no extent: zero end of buffer */
> +		if (ret) {
> +			if (ret > 0)
> +				memset(dest + cur, 0, end - cur);
>   			goto out;
> +		}
>   		fi = btrfs_item_ptr(path.nodes[0], path.slots[0],
>   				    struct btrfs_file_extent_item);
>   		ret = read_and_truncate_page(&path, fi, cur,
>