*at() methods accept -1 for AT_FDCWD

[bhaible]

POSIX ​https://pubs.opengroup.org/onlinepubs/9799919799/functions/readlink.html specifies that the readlinkat() function "shall fail" with error code EBADF if "The path argument does not specify an absolute path and the fd argument is neither AT_FDCWD nor a valid file descriptor open for reading or searching."

This does not work in Haiku hrev57823 (from 2024-07-15): it fails with error code ENOENT instead.

How to reproduce: Compile and run the attached test program.

gcc -Wall foo.c
./a.out

Expected output:

ret = -1, errno == EBADF
OK

Actual output:

ret = -1, errno == No such file or directory
a.out: foo.c:20:main: ret < 0 && errno == EBADF
Kill Thread

[bhaible]

test case foo.c

[waddlesplash]

This, and all the other *at() tickets you have opened today, all have one and the same cause: -1 used to be the value for AT_FDCWD on Haiku. This was changed to -100 so things are clearer, but the kernel still accepts -1 so we don't break ABI too soon. (BeOS did not have AT_FDCWD, so we can change this without breaking ABI with BeOS.)

If one uses a large positive but nonexistent FD, then the tests all work as expected.

[bhaible]

If one uses a large positive but nonexistent FD, then the tests all work as expected.

I confirm this part: I tried fd = 99, and got EBADF in this case.

[waddlesplash]

I've adjusted things in hrev58059 so that the kernel at least rejects anything which isn't -1 or AT_FDCWD, so -2 and other such values should now trigger the error.

Changing this ticket's title and will consolidate the other tickets into it.