The following functions were replaced with their *at variants or
similar:
- lstat -> lstat -> fstatat
- stat -> stat -> fstatat
- fstat -> fstatat
- fchmod -> fchmodat
- fchown -> fchownat
- lchown -> fchownat
- mkfifo -> mkfifoat
- open -> openat
- renameat -> renameat2
- rmdir -> unlinkat
- unlink -> unlinkat
- symlink-> symlinkat
The `open_flags` logic for fstatat was redundant, as this is already
handled (and better so) in `openat2`.
Additionally, the fstatat test succeeds in os-test, and no longer
returns EINVAL. This is because `O_SYMLINK` is no longer
unconditionally passed like it was before. This is a problem because
redoxfs returns EINVAL if a node isn't a symlink but set `O_SYMLINK`.
Linux's variant uses the syscall as intended. Redox's variant uses fpath to build a path to pass to mkdir from the file descriptor plus the file name, which isn't atomic due to the fpath lookup being subject to TOCTOU when paired with mkdir.
Capability based `fchmod`. I also implemented unit tests for chmod,
fchmod, and fchmodat.
The unit tests check Redox-specific behavior, so some of the tests are
disabled for Linux.
Linux's variant uses the syscall as intended. Redox's variant uses fpath
to build a path to pass to fstat from the file descriptor plus the file
name. Unlike the syscall, this isn't atomic so the liminal space between
fpath/getcwd and fstat is subject to TOCTOU.
Beyond fstatat, I moved the stat test to its correct location and added
an assert since the output of the test is unchecked.
I also added AT_FDCWD which seems to be -100 across Unixes. The other
AT_* constants are unimplemented for now.
auronandace