Re: [PATCH v3] xfs: Add check for unsupported xflags

[Xiao Yang <yangx.jy@cn.fujitsu.com>]

On 2020/9/3 15:46, Dave Chinner wrote:
> On Thu, Sep 03, 2020 at 11:57:13AM +0800, Xiao Yang wrote:
>> Current ioctl(FSSETXATTR) ignores unsupported xflags silently
>> so it is not clear for user to know unsupported xflags.
>> For example, use ioctl(FSSETXATTR) to set dax flag on kernel
>> v4.4 which doesn't support dax flag:
>> --------------------------------
>> # xfs_io -f -c "chattr +x" testfile;echo $?
>> 0
>> # xfs_io -c "lsattr" testfile
>> ----------------X testfile
>> --------------------------------
>>
>> Add check to return -EOPNOTSUPP as ext4/f2fs/btrfs does.
>>
>> Signed-off-by: Xiao Yang<yangx.jy@cn.fujitsu.com>
>> Reviewed-by: Darrick J. Wong<darrick.wong@oracle.com>
>> ---
>>   fs/xfs/xfs_ioctl.c | 12 ++++++++++++
>>   1 file changed, 12 insertions(+)
>>
>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>> index 6f22a66777cd..59f9a86f29f7 100644
>> --- a/fs/xfs/xfs_ioctl.c
>> +++ b/fs/xfs/xfs_ioctl.c
>> @@ -1425,6 +1425,14 @@ xfs_ioctl_setattr_check_projid(
>>   	return 0;
>>   }
>>
>> +#define XFS_SUPPORTED_FS_XFLAGS \
>> +	(FS_XFLAG_REALTIME | FS_XFLAG_PREALLOC | FS_XFLAG_IMMUTABLE | \
>> +	 FS_XFLAG_APPEND | FS_XFLAG_SYNC | FS_XFLAG_NOATIME | FS_XFLAG_NODUMP | \
>> +	 FS_XFLAG_RTINHERIT | FS_XFLAG_PROJINHERIT | FS_XFLAG_NOSYMLINKS | \
>> +	 FS_XFLAG_EXTSIZE | FS_XFLAG_EXTSZINHERIT | FS_XFLAG_NODEFRAG | \
>> +	 FS_XFLAG_FILESTREAM | FS_XFLAG_DAX | FS_XFLAG_COWEXTSIZE | \
>> +	 FS_XFLAG_HASATTR)
>> +
>>   STATIC int
>>   xfs_ioctl_setattr(
>>   	xfs_inode_t		*ip,
>> @@ -1439,6 +1447,10 @@ xfs_ioctl_setattr(
>>
>>   	trace_xfs_ioctl_setattr(ip);
>>
>> +	/* Check if fsx_xflags has unsupported xflags */
>> +	if (fa->fsx_xflags&  ~XFS_SUPPORTED_FS_XFLAGS)
>> +                return -EOPNOTSUPP;
> I don't think we can do this as it may break existing applications
> that have been working on XFS for many, many years that don't
> correctly initialise fsx_xflags....
Hi Dave,

It seems that the only way is to keep the current behavior. :-(

By the way, _require_xfs_io_command "chattr" in xfstests cannot check XFS's
unsupported xflags directly because of the behavior, so we may need to check
them by extra xfs_io -c "lsattr".

Best Regards,
Xiao Yang
> Cheers,
>
> Dave.