Re: [PATCH] common: add support for the "local" file system type

[Eryu Guan <eguan@redhat.com>]

On Mon, Sep 26, 2016 at 11:14:31AM -0400, Theodore Ts'o wrote:
> On Mon, Sep 26, 2016 at 09:25:03PM +0800, Eryu Guan wrote:
> > On Fri, Sep 23, 2016 at 04:05:26PM -0400, Theodore Ts'o wrote:
> > > It is sometimes useful to be able to test the local file system
> > > provided in a restricted execution environment (such as that which is
> > > provided by Docker, for example) where it is not possible to mount and
> > > unmount the file system under test.
> > 
> > This looks useful to me. But I'm not sure what other people think.
> > 
> > I tested this patch a bit (ran auto group), noticed some isuses.
> > 
> > - Tests call _require_scratch_shutdown would shutdown your root fs, if
> >   $SCRATCH_MNT is on root fs and root fs is xfs. e.g. generic/044
> > - Tests do freeze/unfreeze would freeze your root fs, e.g. generic/068
> > - Tests fulfill $SCRATCH_DEV would eat all free space on root fs,
> >   because _scratch_mkfs_sized for "local" only checks for lower boundary
> >   but not upper boundary, some tests rely on the upper boundary too,
> >   e.g. generic/027
> > 
> > There might be other issues I didn't notice, since I didn't manage to
> > finish a "FSTYP=local ./check -g auto" run because of above issues.
> 
> Oops, I was testing on small test devices using ext4, so I didn't
> notice these issues.  I'll fix them up.
> 
> > > To support this test case, add support for a new file system type
> > > called "local".  The TEST_DEV and SCRATCH_DEV should be have a
> > > non-block device format (e.g., local:/test or local:/scratch), and the
> > 
> > It's probably good to have a new fstype, as how we test NFS and overlay.
> > i.e. ./check -local, and do all the necessary checks as how we check NFS
> > and overlay setups.
> 
> Even for NFS and overlayfs there are some tests we do where mounting
> and remounting the file system (e.g., with the ro mount option)
> probably does make sense.  Although I do agree there are a large
> number of the NFS mounts and umounts which are largely pointless.
> 
> I was implementing the local file systme type for situations where it
> is simply *not* *possible* at all to mount and unmount the underlying
> file system because it was operating inside a docker container where
> even root didn't have access to modify the supplied file system.
> (Yes, in some cases we could test the underlying file system, but not
> all, and it is useful to have end-to-end tests.)

Sorry, I should have been more clear.

It has nothing to do with mount & umount, it's about adding a new
"-local" option to "check", like "-nfs" and "-overlay". And do
TEST_DEV/TEST_DIR and SCRATCH_DEV/SCRATCH_MNT validations in
_require_test and _require_scratch_nocheck, as how we do the check for
NFS and overlayfs. So we don't have to work around the validation by
specifying TEST_DEV/SCRATCH_DEV in a non-block device format (e.g.
local:/test to mimic an NFS export).

Thanks,
Eryu