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

[Anand Jain <anand.jain@oracle.com>]

On 3/14/19 4:32 PM, Nikolay Borisov wrote:
> 
> 
> 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.

  Right. I wanted to show the bugs, its reason, and fix separately.

> 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.

  Oh. Let me try. Thanks.

-Anand

>> ---
>>   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;
>>