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btrfs: accept and ignore compression level for lzo

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The compression level is meaningless for lzo, but before commit
3f093ccb95 ("btrfs: harden parsing of compression mount options"),
it was silently ignored if passed.

After that commit, passing a level with lzo fails to mount:

    BTRFS error: unrecognized compression value lzo:1

It seems reasonable for users to expect that lzo would permit a numeric
level option, as all the other algos do, even though the kernel's
implementation of LZO currently only supports a single level. Because it
has always worked to pass a level, it seems likely to me that users in
the real world are relying on doing so.

This patch restores the old behavior, giving "lzo:N" the same semantics
as all of the other compression algos.

To be clear, silly variants like "lzo:one", "lzo:the_first_option", or
"lzo:armageddon" also used to work. This isn't meant to suggest that
any possible mis-interpretation of mount options that once worked must
continue to work forever. This is an exceptional case where it makes
sense to preserve compatibility, both because the mis-interpretation is
reasonable, and because nothing tangible is sacrificed.

Finally update btrfs_show_options() to ignore the level of LZO, as it
is only the default level without any extra meaning.

Fixes: 3f093ccb95 ("btrfs: harden parsing of compression mount options")
Reviewed-by: Daniel Vacek <neelx@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Calvin Owens <calvin@wbinvd.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Calvin Owens 2025-08-25 18:32:04 +09:30 committed by David Sterba
parent de134cb54c
commit 6db1df415d
1 changed files with 6 additions and 3 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

9
fs/btrfs/super.c
View file

@ -299,9 +299,12 @@ 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;
ctx->compress_level = btrfs_compress_str2level(BTRFS_COMPRESS_LZO,
string + 3);
if (string[3] == ':' && string[4])
btrfs_warn(NULL, "Compression level ignored for LZO");
btrfs_set_opt(ctx->mount_opt, COMPRESS);
btrfs_clear_opt(ctx->mount_opt, NODATACOW);
btrfs_clear_opt(ctx->mount_opt, NODATASUM);
@ -1079,7 +1082,7 @@ static int btrfs_show_options(struct seq_file *seq, struct dentry *dentry)
seq_printf(seq, ",compress-force=%s", compress_type);
else
seq_printf(seq, ",compress=%s", compress_type);
if (info->compress_level)
if (info->compress_level && info->compress_type != BTRFS_COMPRESS_LZO)
seq_printf(seq, ":%d", info->compress_level);
}
if (btrfs_test_opt(info, NOSSD))