setrlimit silently fails

[smasher164]

Windows build number:

>ver

Microsoft Windows [Version 10.0.18362.295]

What I'm doing and what's happening:

Use any C compiler to produce binaries for WSL and any POSIX for the following source file:

#include <errno.h>
#include <stdio.h>
#include <sys/resource.h>
#include <sys/time.h>
#include <sys/types.h>
#include <unistd.h>

int main() {
  struct rlimit rlp = {1, 4};
  if (setrlimit(RLIMIT_NPROC, &rlp) < 0) goto handle;

  rlp.rlim_cur = 0;
  rlp.rlim_max = 0;
  if (getrlimit(RLIMIT_NPROC, &rlp) < 0) goto handle;
  printf("Process limits: (%llu, %llu)\n", rlp.rlim_cur, rlp.rlim_max);

  if (fork() < 0) goto handle;
  printf("Hello 1\n");
  if (fork() < 0) goto handle;
  printf("Hello 2\n");
  if (fork() < 0) goto handle;
  printf("Hello 3\n");

  return 0;
handle:
  perror(NULL);
  return 1;
}

What's wrong / what should be happening instead:

The outputs on the two systems differ. Here is the correct output produced on my Ubuntu system:

$ ./a.out
Process limits: (1, 4)
Resource temporarily unavailable

And here is the output from WSL(Ubuntu):

$ ./a.out
Process limits: (1, 4)
Hello 1
Hello 1
Hello 2
Hello 2
Hello 2
Hello 2
Hello 3
Hello 3
Hello 3
Hello 3
Hello 3
Hello 3
Hello 3
Hello 3

setrlimit returns 0 to indicate success, even though the hard process limit isn't being set, which permits all of the forks to successfully execute.

Strace of the command here

[therealkenc]

Spiritually similar to #3505. setrlimit(2) on WSL1 is.... limited.