[LTP] [PATCH] tst_device: add new tst_dev_sync

[Petr Vorel <pvorel@suse.cz>]

Hi Li, Cyril,

> > > +before the tst_dev_bytes_written first invocation. And an inline
> > function named
> > > +tst_dev_sync is created for that intention.

> > Other than this it looks good to me, thanks for doing this, acked.

> Pushed.

This broke build with -Werror=implicit-function-declaration [1]:

../include/tst_device.h:78:2: error: implicit declaration of function 'syncfs'; did you mean 'sync'? [-Werror=implicit-function-declaration]
2770  syncfs(fd);
2771  ^~~~~~
2772  sync

The problem is that syncfs() is guarded with __USE_GNU (in glibc, in musl
directly _GNU_SOURCE), so this requires to use _GNU_SOURCE (before including
first header).
Because it's in tst_device.h, we effectively need to build with -D_GNU_SOURCE.
Is that what we want? Or should we always use tst_syscall(__NR_syncfs, fd)
(without conditional check #ifndef HAVE_SYNCFS) ?

Kind regards,
Petr

[1] https://travis-ci.org/linux-test-project/ltp/jobs/634178861