Write a version for pthread_get_name_np

[Konstantin Belousov]

On Sun, Aug 12, 2018 at 10:33:06PM +0200, Willem Jan Withagen wrote:
> Hi,
> 
> For some porting I'm trying to write a pthread_get_name_np(), but
> I have run into a snag....
> Tried some the the procstat code I would come up with:
> 
> int pthread_get_name_np(pthread_t *thread,
>                          char *name, size_t len){
>      struct procstat *procstat;
>      int pid = getpid();
>      unsigned int count, i;
>      struct kinfo_proc *kip, *kipp;
> 
>      procstat = procstat_open_sysctl();
>      kip = procstat_getprocs(procstat, KERN_PROC_PID | KERN_PROC_INC_THREAD,
>              pid, &count);
>      for (i = 0; i < count; i++) {
>          kipp = &kip[i];
>          printf("thread: %ld(0x%lx), %ld(0x%lx)\n", thread, thread,
> kipp->ki_tid, kipp->ki_tid);
>          if (thread == kipp->ki_tid) {
>              kinfo_proc_thread_name(kipp, name, len);
>          }
>      }
>      return 0;
> }
> 
> Problem only is that the TID value in what procstat_getprocs returns in
> ki_tid is nowhere near
> what pthread_self() returns.
> But both manual page and the include file describe the value as Thread ID.
> Only in sys/user.h the type is
>      lwpid_t ki_tid;                 /* XXXKSE thread id */
> 
> What do I need to translate one tid into the other so I can really
> compare them?

You need to cast pthread_t * to struct thread *, this is an internal
libthr structure which represents the thread in userspace.  The
structure field tid gives you the tid you want to pass to sysctl.