Re: [PATCH] linux: return UNSUPPORTED in tst-mount if support_become_root fails

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 14/07/22 00:23, Michael Hudson-Doyle via Libc-alpha wrote:
> Otherwise the test fails if run in a chroot by a non-root user:
> 
> warning: could not become root outside namespace (Operation not permitted)
> ../sysdeps/unix/sysv/linux/tst-mount.c:36: numeric comparison failure
>    left: 1 (0x1); from: errno
>   right: 19 (0x13); from: ENODEV
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:39: not true: fd != -1
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:46: not true: r != -1
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:48: not true: r != -1
> ../sysdeps/unix/sysv/linux/tst-mount.c:52: numeric comparison failure
>    left: 1 (0x1); from: errno
>   right: 9 (0x9); from: EBADF
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:55: not true: mfd != -1
> ../sysdeps/unix/sysv/linux/tst-mount.c:58: numeric comparison failure
>    left: 1 (0x1); from: errno
>   right: 2 (0x2); from: ENOENT
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:61: not true: r != -1
> ../sysdeps/unix/sysv/linux/tst-mount.c:65: numeric comparison failure
>    left: 1 (0x1); from: errno
>   right: 2 (0x2); from: ENOENT
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:68: not true: pfd != -1
> error: ../sysdeps/unix/sysv/linux/tst-mount.c:75: not true: fd_tree != -1
> ../sysdeps/unix/sysv/linux/tst-mount.c:88: numeric comparison failure
>    left: 1 (0x1); from: errno
>   right: 38 (0x26); from: ENOSYS
> error: 12 test failures
> ---
>  sysdeps/unix/sysv/linux/tst-mount.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/tst-mount.c b/sysdeps/unix/sysv/linux/tst-mount.c
> index 502d7e3433..bd75c9e704 100644
> --- a/sysdeps/unix/sysv/linux/tst-mount.c
> +++ b/sysdeps/unix/sysv/linux/tst-mount.c
> @@ -103,7 +103,8 @@ subprocess (void)
>  static int
>  do_test (void)
>  {
> -  support_become_root ();
> +  if (!support_become_root ())
> +    FAIL_UNSUPPORTED("could not become root");
>  

I think the usual way is to check if process can chroot:

  support_become_root ();
  if (!support_can_chroot ())
    return EXIT_UNSUPPORTED;

As done by other tests.

>    pid_t pid = xfork ();
>    if (pid == 0)