Re: [PATCH v3 1/5] btrfs: fix -o compress= level getting inherited by compression xattr property

[Qu Wenruo <wqu@suse.com>]

在 2026/8/10 05:45, Zygo Blaxell 写道:
> On Sun, Aug 09, 2026 at 08:52:59PM +0200, koraynilay wrote:
>> When setting the btrfs.compression xattr, btrfs uses the mount option level
>> (since levels in the xattr aren't supported yet) to compress the data, even
>> if the compression algorithm between the property and the compress= option
>> are different (!!).
>> For example, when mounting with compress=zstd:15 and setting
>> btrfs.compression=zlib, the data would get compressed at zlib:9, because
>> btrfs would take "zlib" from the xattr but "15" from the mount option,
>> which would then get correctly clamped at 9.
>>
>> To fix, just hard-code the compress level at 0, forcing the property's
>> algorithm default.
>>
>> Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org>
>> Signed-off-by: koraynilay <koray.fra@gmail.com>
>> ---
>>   fs/btrfs/inode.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
>> index 2534cd9284d5..6d7f2aa2555c 100644
>> --- a/fs/btrfs/inode.c
>> +++ b/fs/btrfs/inode.c
>> @@ -938,6 +938,7 @@ static void compress_file_range(struct btrfs_work *work)
>>   		compress_level = inode->defrag_compress_level;
>>   	} else if (inode->prop_compress) {
>>   		compress_type = inode->prop_compress;
>> +		compress_level = 0;
> 
> This set to zero should be conditional on inode->prop_compress !=
> fs_info->compress_type; otherwise, it prevents the compress-level mount
> option from working in the common case where 'btrfs.compression=zstd'
> or 'chattr +c' has been set.

No, read this discussion.

https://lore.kernel.org/linux-btrfs/DKK0XWCI89MM.2G6KD41GSR46J@gmail.com/T/#m79e6c1ecbcc61ebb57dca5cbb3eceabd052ecdbc

> 
>>   	}
>>   
>>   	/* Compression level is applied here. */
>> @@ -2326,6 +2327,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f
>>   			compress_level = inode->defrag_compress_level;
>>   		} else if (inode->prop_compress) {
>>   			compress_type = inode->prop_compress;
>> +			compress_level = 0;
>>   		}
>>   		cb = btrfs_compress_bio(inode, 0, blocksize, compress_type, compress_level, 0);
>>   		if (IS_ERR(cb)) {
>> -- 
>> 2.55.0
>>
>>