Re: [PATCH 2/4] btrfs: fix vanished compression property after failed set

[Nikolay Borisov <nborisov@suse.com>]

On 14.03.19 г. 7:05 ч., Anand Jain wrote:
> The compression property resets to NULL, instead of the old value if we
> fail to set the new compression parameter.
> 
> btrfs prop get /btrfs compression
>   compression=lzo
> btrfs prop set /btrfs compression zli
>   ERROR: failed to set compression for /btrfs: Invalid argument
> btrfs prop get /btrfs compression
> 
> This is because the compression property ->validate() is successful for
> 'zli' as the strncmp() used the len passed from the userland.
> 
> Fix it by using the expected string length in strncmp().
> 
> Signed-off-by: Anand Jain <anand.jain@oracle.com>

The changelog could be a bit clearer. The failure is due to the fact
that ->validate succeeds but ->apply fails and the handling code calls

	btrfs_setxattr(trans, inode, handler->xattr_name,
              NULL, 0, flags);

However, if you make this patch be the first in the series you obsolete
the existing patch 1 and fix the issue in this one. I.e 2 birds with 1
stone.

Also I believe btrfs/048 could use some extension in the part where it
validates compression properties to test for the bugs discovered/fixed
in this series.

> ---
>  fs/btrfs/props.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/btrfs/props.c b/fs/btrfs/props.c
> index 3cc007e3c7f8..72a06c4d3c70 100644
> --- a/fs/btrfs/props.c
> +++ b/fs/btrfs/props.c
> @@ -275,11 +275,11 @@ static int prop_compression_validate(const char *value, size_t len)
>  	if (!value)
>  		return 0;
>  
> -	if (!strncmp("lzo", value, len))
> +	if (!strncmp("lzo", value, 3))
>  		return 0;
> -	else if (!strncmp("zlib", value, len))
> +	else if (!strncmp("zlib", value, 4))
>  		return 0;
> -	else if (!strncmp("zstd", value, len))
> +	else if (!strncmp("zstd", value, 4))
>  		return 0;
>  
>  	return -EINVAL;
>