[LTP] [PATCH v2] syscalls: add syscall syncfs test

Cyril Hrubis chrubis@suse.cz
Mon Feb 18 13:24:53 CET 2019

> > >> Thanks for the pointers. IIUC, you are referring to following change:
> > >>
> > >> -       TEST(syncfs(fd));
> > >> +       TEST(tst_syscall(__NR_syncfs, fd));
> > >>
> > >> If yes, then I will incorporate it.
> > >
> > > The most complete solution is configure check + fallback definition.
> > >
> > > Have a look at:
> > >
> > > include/lapi/execveat.h
> > > m4/ltp-execveat.m4
> > > configure.ac
> >
> > For tests in testcases/kernel/syscalls, should the tests typically
> > directly call the syscall? I'd think this is preferable to the use of C
> > library wrappers as these tests (by their location in the tree) seem to
> > be focused on the syscall functionality in the kernel.
> >
> Sounds reasonable to me. But as per following manpage text for syscall():
> "Each architecture ABI has its own requirements on how system call
> arguments are passed to the kernel.  For system calls that have a
> glibc  wrapper  (e.g., most  system  calls), glibc handles the details
> of copying arguments to the right registers in a manner suitable for
> the architecture. However, when using syscall() to make a system call,
> the caller might need to handle architecture-dependent details; this
> requirement is most commonly encountered  on certain 32-bit
> architectures."
> So I am not sure how we handle this architecture specific stuff if
> required in test-cases.

In more than 99% of the cases this is not an issue, as far as the
arguments are passed as long int and we do not have to pass more than
six, which is the common case, we don't have to do anything.

In some cases we have to split 64bit values in half and pass them as two
arguments, then we put the code into the lapi hader such as

Then there are cases where we pass a pointer to architecture specific
structure such as the sigaction which sometimes contains a pointer to
function that restores the program state after we return from the signal
handler and this is where calling the kernel syscall directly gets
complex. We do carry that code under include/lapi/rt_sigaction.h.

Cyril Hrubis

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