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

[Qu Wenruo]

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@xxxxxxxxxx>
> > > ---
> > >    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);