Re: [LTP] [PATCH v2 03/10] setxattr01: add setxattrat variant

[Cyril Hrubis <chrubis@suse.cz>]

Hi!
> > Can we please, in a subsequent patch, convert this part to our standard
> > approach where we check for the availability in the test setup and
> > expect the syscalls to be present if kernel is new enough?
> 
> What do you think it's the best way? Some of these tests have multiple
> syscalls related to *xattrat and in this test in particular we are
> testing 2 syscalls.

The same what we do for the rest of the syscalls, introduce a
setxattrat_supported() helper into a shared header that would call
tst_brk(TCONF, "") if kernel is older than the version the syscall was
added to and we got ENOSYS.

We actually have to handle a few cases here:

For setxattrat:
  - ENOSYS -> kernel too old
  - EOPNOTSUPP -> filesystem does not support extended attributes
                  (e.g. vfat)

And as for filesystem support, it looks like TMPFS has
CONFIG_TMPFS_XATTR option so it could be enabled or disabled, however
they should be supported for native Linux filesystems such as ext, btrfs
or xfs.

And we have to handle EOPNOTSUPP for setxattr() as well, so the test
setup would look like:

	if (tst_variant)
		setxattrat_supported();
	else
		setxattr_supported();

At the moment the ENOSYS branch would be covered by the fallback
function since it calls tst_syscall() but once the function gets added
to libc the check would no longer happen, so we need to eventually
handle the ENOSYS in the foo_supported() function as well.

> Maybe the best way would be to check for HAVE_FUNC_* declarations in
> this case, but then fallback function would fail anyway.

No this does not work, the only way how to find out if a syscall is
supported is to call it and check the return value.

-- 
Cyril Hrubis
chrubis@suse.cz

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