Re: [PATCH] btrfs: prevent remounting to v1 space cache for subpage mount

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/5/16 23:05, Josef Bacik wrote:
> On Mon, May 16, 2022 at 02:26:53PM +0800, Qu Wenruo wrote:
>> Upstream commit 9f73f1aef98b ("btrfs: force v2 space cache usage for
>> subpage mount") forces subpage mount to use v2 cache, to avoid
>> deprecated v1 cache which doesn't support subpage properly.
>>
>> But there is a loophole that user can still remount to v1 cache.
>>
>> The existing check will only give users a warning, but not really
>> prevents the users to do the remount.
>>
>> Although remounting to v1 will not cause any problems since the v1 cache
>> will always be marked invalid when mounted with a different page size,
>> it's still better to prevent v1 cache at all for subpage mounts.
>>
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   fs/btrfs/super.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
>> index b1fdc6a26c76..1617528a3367 100644
>> --- a/fs/btrfs/super.c
>> +++ b/fs/btrfs/super.c
>> @@ -1985,6 +1985,14 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
>>   	if (ret)
>>   		goto restore;
>>
>> +	/* V1 cache is not supported for subpage mount. */
>> +	if (fs_info->sectorsize < PAGE_SIZE &&
>> +	    btrfs_test_opt(fs_info, SPACE_CACHE)) {
>> +		btrfs_warn(fs_info,
>> +	"v1 space cache is not supported for page size %lu with sectorsize %u",
>> +			   PAGE_SIZE, fs_info->sectorsize);
>
> Shouldn't we be doing ret = -EINVAL; here?  Thanks,
>
> Josef

Oh, forgot that.

Thanks for catching it,
Qu