Re: [RFC PATCH] fstests: generic: Test that fsync works on file in overlayfs merged directory

[Eric Sandeen <sandeen@sandeen.net>]

On 9/30/15 4:56 PM, Dave Chinner wrote:
> On Wed, Sep 30, 2015 at 10:57:45PM +0300, Roman Lebedev wrote:
>> As per overlayfs documentation, any activity on a merged directory
>> for a application that is doing such activity should work exactly
>> as if that would be a normal, non overlayfs-merged directory.
>>
>> That is, e.g. simple fopen-fwrite-fsync-fclose sequence should
>> work just fine.
> 
> We have plenty of tests that do things like that.
> 
>> But apparently it does not. Add a simple generic test to check that.
>> As of right now (linux-4.2.1) this test fails at least on btrfs.
>>
>> PS: An alternative (and probably better approach) would be to run
>> fstests test suite with TEST_DIR set to overlayfs work directory.
> 
> Much better is to run xfstests directly on overlayfs. THere have
> been some patches to do that posted in the past, but those patches
> and discussions kinda ended up going nowhere:
> 
> http://www.mail-archive.com/fstests@vger.kernel.org/msg00474.html
> 
> Perhaps you'd like to pick this up, and then overlay will by much
> easier to test and hence likely not to have bugs like this...

Yeah, that could still be used for fun, but Zach's POV was that
we should just have a specific overlayfs config (dictating paths
to over/under/merge/around/through/whatever directories), a special
mount_overlayfs helper, etc, ala NFS & CIFS.  It may actually be
easier than what I proposed.

If you want to take a stab at it I'm happy to help, answer questions,
etc - I'm not sure when I'll get back to it...

-Eric