[RFC] set the thread name

[RFC] set the thread name

[Stefani Seibold]

Currently it is not easy to identify a thread in linux, because there is
no thread name like in some other OS. 

If there were are thread name then we could extend a kernel segv message
and the /proc/<pid>/task/<tid>/... entries by a TName value like this:

cat /proc/492/task/495/status
Name:   test
TName:  RX-Data          <- this is the thread identification field
State:  S (sleeping)
Tgid:   492
Pid:    495
PPid:   1
.
.
.

This will it make much easier to determinate which thread id is
associated to a logical thread.

It would be possible do this without add a new entry to the task_struct.
Just use the comm entry which is available, because it has the same
value as the group_leader->comm entry.

The only thing to do is to replace all task_struct->comm access by
task_struct->group_leader->comm to have the old behavior. This can be
eventually encapsulated by a macro.

The task_struct->comm of a non group_leader would be than the name of
the thread.

The only drawback is that there are a lot of files which must be
modified. A quick
 find linux-2.6.30 -type f | xargs grep -l -e "->comm\>"  | wc -l
shows 215 files. But this can be handled.

So i propose a new system call to give a thread a name.

What do you think?

Greetings,
Stefani


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Re: [RFC] set the thread name

[Bert Wesarg]

Hi,

On Tue, Jun 16, 2009 at 20:39, Stefani Seibold<stefani@seibold.net> wrote:
> Currently it is not easy to identify a thread in linux, because there is
> no thread name like in some other OS.
>
> If there were are thread name then we could extend a kernel segv message
> and the /proc/<pid>/task/<tid>/... entries by a TName value like this:
prctl(PR_SET_NAME, ...) works perfectly here.

Bert

/* -*- c -*- */

#define _GNU_SOURCE
#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <stdbool.h>
#include <math.h>
#include <pthread.h>
#include <sys/prctl.h>

void *
thread(void *arg)
{
    unsigned long i = (unsigned long)arg;
    char comm[16];
    snprintf(comm, sizeof comm, "task %02lu", i);
    prctl(PR_SET_NAME, comm, 0l, 0l, 0l);

    sleep(10);

    return NULL;
}

int
main(int ac, char *av[])
{
    pthread_t thr;
    unsigned long i, n = 10;
    char comm[16];

    printf("%u\n", getpid());
    sleep(5);
    snprintf(comm, sizeof comm, "master");
    prctl(PR_SET_NAME, comm, 0l, 0l, 0l);
    sleep(5);

    for (i = 0; i < n; i++)
        pthread_create(&thr, NULL, thread, (void *)i);

    pthread_join(thr, NULL);

    return 0;
}

>
> Greetings,
> Stefani
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> the body of a message to majordomo@vger.kernel.org
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> Please read the FAQ at  http://www.tux.org/lkml/
>

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Re: [RFC] set the thread name

[Stefani Seibold]

Am Dienstag, den 16.06.2009, 21:14 +0200 schrieb Bert Wesarg:
> Hi,
> 
> On Tue, Jun 16, 2009 at 20:39, Stefani Seibold<stefani@seibold.net> wrote:
> > Currently it is not easy to identify a thread in linux, because there is
> > no thread name like in some other OS.
> >
> > If there were are thread name then we could extend a kernel segv message
> > and the /proc/<pid>/task/<tid>/... entries by a TName value like this:
> prctl(PR_SET_NAME, ...) works perfectly here.
> 
Ooops... I did not noticed that this is already implemented. Thats works
perfectly ;-)



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Re: [RFC] set the thread name

[Stefani Seibold]

Am Dienstag, den 16.06.2009, 21:14 +0200 schrieb Bert Wesarg:
> Hi,
> 
> On Tue, Jun 16, 2009 at 20:39, Stefani Seibold<stefani@seibold.net> wrote:
> > Currently it is not easy to identify a thread in linux, because there is
> > no thread name like in some other OS.
> >
> > If there were are thread name then we could extend a kernel segv message
> > and the /proc/<pid>/task/<tid>/... entries by a TName value like this:
> prctl(PR_SET_NAME, ...) works perfectly here.
> 

I checked it now a little bit more. It is true it works, but if i do a
segv access inside a thread a get the kernel message like:

task 09[17395]: segfault at 0 ip 08048612 sp b363c370 error 6 in
a.out[8048000+1000]

So the current implementation is not exactly what i expect. I would
prefer my solution to replace every access thread_struct->comm to
task_struct->group_leader->comm to have the right behavior.

The new system call is obsolete, it is still there.


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Re: [RFC] set the thread name

[KOSAKI Motohiro]

(cc to linux-api)

> Hi,
> 
> On Tue, Jun 16, 2009 at 20:39, Stefani Seibold<stefani@seibold.net> wrote:
> > Currently it is not easy to identify a thread in linux, because there is
> > no thread name like in some other OS.
> >
> > If there were are thread name then we could extend a kernel segv message
> > and the /proc/<pid>/task/<tid>/... entries by a TName value like this:
> prctl(PR_SET_NAME, ...) works perfectly here.

Oops, but man page describe another thing.

       PR_SET_NAME
              (Since Linux 2.6.9) Set the process name for the calling process
              to arg2.                    ^^^^^^^^^^^^

Should we change man page? or change implementation?

I bet many developer assume the implementation is right.


> 
> Bert
> 
> /* -*- c -*- */
> 
> #define _GNU_SOURCE
> #include <unistd.h>
> #include <stdlib.h>
> #include <stdio.h>
> #include <string.h>
> #include <stdint.h>
> #include <stdbool.h>
> #include <math.h>
> #include <pthread.h>
> #include <sys/prctl.h>
> 
> void *
> thread(void *arg)
> {
>     unsigned long i = (unsigned long)arg;
>     char comm[16];
>     snprintf(comm, sizeof comm, "task %02lu", i);
>     prctl(PR_SET_NAME, comm, 0l, 0l, 0l);
> 
>     sleep(10);
> 
>     return NULL;
> }
> 
> int
> main(int ac, char *av[])
> {
>     pthread_t thr;
>     unsigned long i, n = 10;
>     char comm[16];
> 
>     printf("%u\n", getpid());
>     sleep(5);
>     snprintf(comm, sizeof comm, "master");
>     prctl(PR_SET_NAME, comm, 0l, 0l, 0l);
>     sleep(5);
> 
>     for (i = 0; i < n; i++)
>         pthread_create(&thr, NULL, thread, (void *)i);
> 
>     pthread_join(thr, NULL);
> 
>     return 0;
> }
> 
> >
> > Greetings,
> > Stefani
> >
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at ?http://vger.kernel.org/majordomo-info.html
> > Please read the FAQ at ?http://www.tux.org/lkml/
> >
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