linux-kernel - Re: [PATCH] btrfs: Accept and ignore compression level for lzo

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Message-ID: <9bdb2726-de7b-4ef0-9ad5-7050d214a85f@suse.com>
Date: Fri, 22 Aug 2025 19:48:16 +0930
From: Qu Wenruo <wqu@...e.com>
To: Calvin Owens <calvin@...nvd.org>, Qu Wenruo <quwenruo.btrfs@....com>
Cc: linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
 Daniel Vacek <neelx@...e.com>, David Sterba <dsterba@...e.com>,
 Josef Bacik <josef@...icpanda.com>, Chris Mason <clm@...com>
Subject: Re: [PATCH] btrfs: Accept and ignore compression level for lzo



在 2025/8/22 18:58, Calvin Owens 写道:
> On Friday 08/22 at 17:57 +0930, Qu Wenruo wrote:
>> 在 2025/8/22 17:15, Calvin Owens 写道:
>>> The compression level is meaningless for lzo, but before commit
>>> 3f093ccb95f30 ("btrfs: harden parsing of compression mount options"),
>>> it was silently ignored if passed.
>>
>> Since LZO doesn't support compression level, why providing a level parameter
>> in the first place?
> 
> Interpreting "no level" as "level is always one" doesn't seem that
> unreasonable to me, especially since it has worked forever.

No means no, period.

> 
>> I think it's time for those users to properly update their mount options.
> 
> It's a user visable regression, and fixing it has zero possible
> downside. I think you should take my patch :)

I do not want to encourage such usage.

Sanity overrides "regression". If it shouldn't work in the first place, 
it's not a regression.

> 
> Thanks,
> Calvin
> 
>>>
>>> After that commit, passing a level with lzo fails to mount:
>>>
>>>       BTRFS error: unrecognized compression value lzo:1
>>>
>>> Restore the old behavior, in case any users were relying on it.
>>>
>>> Fixes: 3f093ccb95f30 ("btrfs: harden parsing of compression mount options")
>>> Signed-off-by: Calvin Owens <calvin@...nvd.org>
>>> ---
>>>    fs/btrfs/super.c | 2 +-
>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>>> index a262b494a89f..7ee35038c7fb 100644
>>> --- a/fs/btrfs/super.c
>>> +++ b/fs/btrfs/super.c
>>> @@ -299,7 +299,7 @@ static int btrfs_parse_compress(struct btrfs_fs_context *ctx,
>>>    		btrfs_set_opt(ctx->mount_opt, COMPRESS);
>>>    		btrfs_clear_opt(ctx->mount_opt, NODATACOW);
>>>    		btrfs_clear_opt(ctx->mount_opt, NODATASUM);
>>> -	} else if (btrfs_match_compress_type(string, "lzo", false)) {
>>> +	} else if (btrfs_match_compress_type(string, "lzo", true)) {
>>>    		ctx->compress_type = BTRFS_COMPRESS_LZO;
>>>    		ctx->compress_level = 0;
>>>    		btrfs_set_opt(ctx->mount_opt, COMPRESS);
>>
>