[LTP] [RFC][PATCH 1/2] libltp: add support to mount tmpfs

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> Hi!
> > Some tests go through losetup, create, format and mount
> > filesystems only to run tests for 'EROFS' return value from
> > system calls. The tests end up being flaky depending on the tools
> > available on the platform. e.g. mkfs.<filesystem> tool is required for
> > mounting a device with filesystem.
> > 
> > If the test is only to check for EROFS, this can be achieved by simply
> > doing a 'tmpfs' read-only mount in $tmpdir.
> 
> Using tmpfs for EROFS sounds like a good idea, that should be much
> faster than loop device as well, but there is a catch. There most likely
> are embedded Linux devices that do not have tmpfs support compiled in
> and as it is this would break these testcases on such platforms.
> 
> What about we created even more high-level interface for this? For
> instance we can add .needs_rofs flag to the tst_test structure (reuse
> the mntpoint to mount it) and let the library handle the details. I.e.
> go for tmpfs and if that fails fall back to loop mounted device.

Can we bind mount "/" as read-only somewhere to $tmpdir? That should be
widely supported (MS_BIND since 2.4).