Date: Mon, 13 Aug 2018 01:36:28 +0200 From: Willem Jan Withagen <wjw@digiware.nl> To: Konstantin Belousov <kostikbel@gmail.com> Cc: FreeBSD Hackers <freebsd-hackers@freebsd.org> Subject: Re: Write a version for pthread_get_name_np Message-ID: <c99da03d-596f-9773-ab5b-df5c9d30fa27@digiware.nl> In-Reply-To: <20180812225726.GC2340@kib.kiev.ua> References: <7fa2b876-9397-da2b-cb29-56badf11b66d@ecoracks.nl> <42689feb-9bd4-429b-63d7-b9193123ee47@digiware.nl> <20180812205835.GB2340@kib.kiev.ua> <bdf7e3bd-e33f-019e-c6ff-a10e927e3a01@digiware.nl> <20180812225726.GC2340@kib.kiev.ua>
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On 13/08/2018 00:57, Konstantin Belousov wrote:
> On Mon, Aug 13, 2018 at 12:01:03AM +0200, Willem Jan Withagen wrote:
>> On 12/08/2018 22:58, Konstantin Belousov wrote:
>>> 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,
>>>> ššššššššššššššššššššššš char *name, size_t len){
>>>> ššš struct procstat *procstat;
>>>> ššš int pid = getpid();
>>>> ššš unsigned int count, i;
>>>> ššš struct kinfo_proc *kip, *kipp;
>>>>
>>>> ššš procstat = procstat_open_sysctl();
>>>> ššš kip = procstat_getprocs(procstat, KERN_PROC_PID | KERN_PROC_INC_THREAD,
>>>> ššššššššššš pid, &count);
>>>> ššš for (i = 0; i < count; i++) {
>>>> ššš ššš kipp = &kip[i];
>>>> ššš ššš printf("thread: %ld(0x%lx), %ld(0x%lx)\n", thread, thread,
>>>> kipp->ki_tid, kipp->ki_tid);
>>>> ššš ššš if (thread == kipp->ki_tid) {
>>>> ššš ššš ššš kinfo_proc_thread_name(kipp, name, len);
>>>> ššš ššš }
>>>> ššš }
>>>> ššš 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
>>>> ššš lwpid_t ki_tid;šššššššššššššššš /* 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.
>>
>> mmmm,
>>
>> I'm afraid I'm not quit able to followup on your answer.
>>
>> Trying to find what to include to be able to cast this, I can only find
>> a small bit defined in /usr/src/lib/libthr/thread/thr_private.h.
>> /*
>> * lwpid_t is 32bit but kernel thr API exports tid as long type
>> * to preserve the ABI for M:N model in very early date (r131431).
>> */
>> #define TID(thread) ((uint32_t) ((thread)->tid))
>>
>> But that I cannot just "include" that file without a lot of mess, and
>> then still it does not compile.
>>
>> So could you point me to where this private part of struct thread is
>> hidding?
> I do not understand your confusion. The thr_private.h header is only
> for use by libthr, the FreeBSD threading library implementation. The
> function that you are trying to implement, requires understanding of the
> libthr internals and can only be implemented as part of libthr.
>
> Any other attempt to translate libthr handle for thread into tid needs
> same access to the struct pthread.
Oke,
I don't have more knowledge of (p)threads than just how to use it.
I was trying to do this as a piece of code in the compat.cc of my ceph port.
But trying to reread what you write is boils down to: there is no way to
link a value returned by (struct pthread *)pthread_self() to the kd_tid
value that can be found in the (struct kinfo_proc *) describing that
same thread.
And even though (struct thread *) has a field:
lwpid_t td_tid; /* (b) Thread ID. */
that field seems to be stuck at value td_tid = 32767 every time I look
at it with gdb.
So it is a pity that this is not going to work this way.
--WjW
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