consequences of XFS_IOC_FSSETXATTR on non-empty file?

[Ilya Dryomov]

On Sun, Jul 13, 2014 at 5:48 AM, Samuel Just <sam.just at inktank.com> wrote:
> Actually, on this ubuntu kernel (3.13.0-24-generic), it doesn't seem
> to give an error.  I'll attach my test case for that.  We don't yet
> have a way of reproducing the corruption -- the ext_size change in the
> osd simply seemed like a promising lead.
> -Sam
>
> On Sat, Jul 12, 2014 at 6:26 PM, Dave Chinner <david at fromorbit.com> wrote:
>> On Sat, Jul 12, 2014 at 06:16:54PM -0700, Samuel Just wrote:
>>> Hi,
>>>
>>> We are seeing reports of ceph-osd stores on xfs of files with some
>>> garbage data (possibly misplaced from data elsewhere in the
>>> filesystem).  There was a bug for a while where the ceph-osd process
>>> would set a value for fsx_extsize on a non-empty (possibly sparse)
>>> file using XFS_IOC_FSSETXATTR.  Could that plausibly result in a file
>>> with garbage data?
>>
>> No, setting an extent size on a non-empty file will simply fail
>> with EINVAL.

AFAIR it checks whether or not any extents are actually allocated, not
whether the file is empty or not.  I think if you call fsync() or even
fdatasync() before close(fd), it will fail as expected.

Thanks,

                Ilya