[PATCH] getlogin_r: return early when linux sentinel value is set

[Adhemerval Zanella]

On 17/03/2018 00:18, Jesse Hathaway wrote:
> When there is no login uid Linux sets /proc/self/loginid to the sentinel
> value of 4294967295. If this is set we can return early and avoid
> needlessly looking up the sentinel value in any configured nss
> databases.

The change is short enough so I think it won't require a copyright
assignment.  However it does require a ChangeLog entry, could you please
resend the patch with a proper one?

> 
> diff --git a/sysdeps/unix/sysv/linux/getlogin_r.c
> b/sysdeps/unix/sysv/linux/getlogin_r.c
> index 73ea14c8f9..43f55a2188 100644
> --- a/sysdeps/unix/sysv/linux/getlogin_r.c
> +++ b/sysdeps/unix/sysv/linux/getlogin_r.c
> @@ -55,6 +55,12 @@ __getlogin_r_loginuid (char *name, size_t namesize)
>     endp == uidbuf || *endp != '\0'))
>      return -1;
> 
> +  /* If there is no login uid, linux sets /proc/self/loginid to the sentinel
> +     value of 4294967295, so check if the value is set and return early to
> +     avoid making unneeded nss lookups. */
> +  if (uid == 4294967295)
> +    return ENXIO;

I prefer to just use either (int)-1 or just 0xffffffff.  Also,
__getlogin_r_loginuid should set errno itself as for ERANGE instead
of just return its value (errno won't be set in this case and I think
it got it wrong for ENOMEM in this case).

> +
>    struct passwd pwd;
>    struct passwd *tpwd;
>    int result = 0;
>