ZTS: small fix for SEEK_DATA/SEEK_HOLE tests

[mcmilk]

Motivation and Context

Some libc's like uClibc lag the proper definition of SEEK_DATA and SEEK_HOLE.
Since we have only two files in ZTS which use these definitons, let's define them by hand.

There should be no failures, because:

• FreeBSD has support for SEEK_DATA/SEEK_HOLE since FreeBSD 8
• Linux has it since Linux 3.1
• the libc will submit the parameters unchanged to the kernel

There is another pull request for fixing this by skipping the tests here: #16169.
This one is a bit more complex and not finished currently.

Description

I would prefer to make the needed definitions by hand for now:

#ifndef SEEK_DATA
#define SEEK_DATA 3
#endif
#ifndef SEEK_HOLE
#define SEEK_HOLE 4
#endif

Some more details about the Defines themself:

• FreeBSD has SEEK_DATA/SEEK_HOLE since april 2007 (FreeBSD 8): freebsd/freebsd-src@f6521d1
• Linux has it since around 2011 (Linux 3.1): torvalds/linux@982d816
• POSIX has it defined also now: https://www.austingroupbugs.net/view.php?id=415
• musl supports it: kraj/musl@cbacd63
• uClibc will hopefully apply them in near future also

So in the end, ZTS uses the Defines here:

1. tests/zfs-tests/cmd/mmap_seek.c
2. tests/zfs-tests/tests/functional/cp_files/seekflood.c

So let's define them in order to do the tests on uClibc based ZTS runs also.

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[jlsalvador]

Are you sure that defining this does not crash at runtime?

https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/sysdeps/linux/common/lseek.c?id=05b11809bd11450aff3d20e43f18415ce58601e7#n44

	switch(whence) {
		case SEEK_SET:
		case SEEK_CUR:
		case SEEK_END:
			break;
		default:
			__set_errno(EINVAL);
			return -1;
	}

[mcmilk]

Are you sure that defining this does not crash at runtime?

The test will fail then, because the seek will return -1, that should be fine.

https://github.com/kraj/uclibc-ng/blob/dc3ad9110793e67b13421135f714085cb8ab3c68/libc/sysdeps/linux/common/lseek.c#L39

	switch(whence) {
		case SEEK_SET:
		case SEEK_CUR:
		case SEEK_END:
			break;
		default:
			__set_errno(EINVAL);
			return -1;
	}

I didn't check uClibc itself. Is there a way that uClibc will get support for it?

Edit: oh, uClibc was last updated in 2012?!

I can change my PR so that it handles EINVAL ... and creates a skipped test.

[jlsalvador]

I have already tested this patch for Buildroot (uClibc). It works correctly 👏. Thank you all!