[libc] Implement chown

[michaelrj-google]

Described in POSIX: https://pubs.opengroup.org/onlinepubs/9799919799/functions/chown.html

The chown is a syscall wrapper for updating the ownership of a file.

Here's a checklist for what you'll need to do for this:

• Add the implementation of chown in /src/unistd
• Add tests for chown in /test/src/unistd (they don't need to test much, just make sure the syscall wrapper passes and fails appropriately)
• Add chown to entrypoints.txt for at least x86_64 and whatever you're building on
• Add chown to include/unistd.yaml

[llvmbot]

@llvm/issue-subscribers-libc

Author: Michael Jones (michaelrj-google)

Described in POSIX: https://pubs.opengroup.org/onlinepubs/9799919799/functions/chown.html

The chown is a syscall wrapper for updating the ownership of a file.

Here's a checklist for what you'll need to do for this:

• Add the implementation of chown in /src/unistd
• Add tests for chown in /test/src/unistd (they don't need to test much, just make sure the syscall wrapper passes and fails appropriately)
• Add chown to entrypoints.txt for at least x86_64 and whatever you're building on
• Add chown to include/unistd.yaml

[shubhe25p]

Thanks for creating the issue, can I please work on it?

[shubhe25p]

Two small questions @michaelrj-google :

1. Type gid_t is not present in libc/hdr/types, can I import llvm-libc/types?

2. For tests, do I need to check for all error codes?

Apologies if the questions are too naive.

[michaelrj-google]

1. You should add a new header for gid_t.h in libc/hdr/types. It should look basically the same as the header for uid_t.
2. You don't need to check all the error codes, just that the function passes and fails. We want to check all of the branches in the function, and since it's a syscall wrapper it should only have one branch.

Don't worry about asking naive questions, it's an important step to learning.

[shubhe25p]

Thank you so much

[michaelrj-google]

Fixed by #166434