Re: [PATCH v2 1/2] btrfs: add support for SUPER_FLAG_CHANGING_FSID in btrfs.ko

[Anand Jain <anand.jain@oracle.com>]

On 01/08/2018 01:08 PM, Qu Wenruo wrote:
> 
> 
> On 2018年01月08日 13:04, Anand Jain wrote:
>> Userland sets SUPER_FLAG_CHANGING_FSID and resets it only when changing
>> fsid is complete. Its not a good idea to mount the device anything in
>> between, so this patch fails the mount if SB SUPER_FLAG_CHANGING_FSID
>> is set.
>>
>> Signed-off-by: Anand Jain <anand.jain@oracle.com>
>>    cc: wqu@suse.com
>> ---
>> v1->v2: Oops. Fix cut and paste error, remove ~. My bad.
>>
>>   fs/btrfs/disk-io.c              | 7 ++++++-
>>   include/uapi/linux/btrfs_tree.h | 1 +
>>   2 files changed, 7 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index a69e5944dc08..0dd215258ff9 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -61,7 +61,8 @@
>>   				 BTRFS_HEADER_FLAG_RELOC |\
>>   				 BTRFS_SUPER_FLAG_ERROR |\
>>   				 BTRFS_SUPER_FLAG_SEEDING |\
>> -				 BTRFS_SUPER_FLAG_METADUMP)
>> +				 BTRFS_SUPER_FLAG_METADUMP |\
>> +				 BTRFS_SUPER_FLAG_CHANGING_FSID)
> 
> Still the same problem here.
> 
> Since that super flag is excluded in btrfs_check_super_valid(), I didn't
> see any meaning including it into BTRFS_SUPER_FLAG_SUPP, and it will
> confuse later BTRFS_SUPER_FLAG_SUPP users.


  Anyway BTRFS_SUPER_FLAG_SUPP as such does not stop to mount, it
  just warns. So when there is a new flag which is not supported
  we get this warning. As in the case with BTRFS_SUPER_FLAG_METADUMP_V2.
  BTRFS_SUPER_FLAG_METADUMP_V2 in kernel is defined but not supported.
  However since we are supporting BTRFS_SUPER_FLAG_CHANGING_FSID, so
  adding to BTRFS_SUPER_FLAG_SUPP make sense to me. ?

Thanks, Anand


> Thanks,
> Qu
> 
>>   
>>   static const struct extent_io_ops btree_extent_io_ops;
>>   static void end_workqueue_fn(struct btrfs_work *work);
>> @@ -3906,6 +3907,10 @@ static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info)
>>   		btrfs_err(fs_info, "no valid FS found");
>>   		ret = -EINVAL;
>>   	}
>> +	if (btrfs_super_flags(sb) & BTRFS_SUPER_FLAG_CHANGING_FSID) {
>> +		btrfs_err(fs_info, "SUPER_FLAG_CHANGING_FSID is set");
>> +		ret = -EINVAL;
>> +	}
>>   	if (btrfs_super_flags(sb) & ~BTRFS_SUPER_FLAG_SUPP)
>>   		btrfs_warn(fs_info, "unrecognized super flag: %llu",
>>   				btrfs_super_flags(sb) & ~BTRFS_SUPER_FLAG_SUPP);
>> diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
>> index 38ab0e06259a..aff1356c2bb8 100644
>> --- a/include/uapi/linux/btrfs_tree.h
>> +++ b/include/uapi/linux/btrfs_tree.h
>> @@ -457,6 +457,7 @@ struct btrfs_free_space_header {
>>   #define BTRFS_SUPER_FLAG_SEEDING	(1ULL << 32)
>>   #define BTRFS_SUPER_FLAG_METADUMP	(1ULL << 33)
>>   #define BTRFS_SUPER_FLAG_METADUMP_V2	(1ULL << 34)
>> +#define BTRFS_SUPER_FLAG_CHANGING_FSID	(1ULL << 35)
>>   
>>   
>>   /*
>>
>