Change processname for dmix/dsnoop process

Change processname for dmix/dsnoop process

[Gregor Jasny]

Hi,

At the moment the dmix process inherits the processname from the first 
dmix enabled process. This can be very confusing.

It would be nice if dmix or dsnoop would change its name after forking.

Thanks,
Gregor


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Re: Change processname for dmix/dsnoop process

[Takashi Iwai]

At Fri, 30 Sep 2005 16:18:02 +0200,
Gregor Jasny wrote:
> 
> Hi,
> 
> At the moment the dmix process inherits the processname from the first 
> dmix enabled process. This can be very confusing.
> 
> It would be nice if dmix or dsnoop would change its name after forking.

Well, changing the process name in run time is very tricky on Linux.
In other words: no proper way.


Takashi


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Re: Change processname for dmix/dsnoop process

[Mike Hearn]

On Fri, 30 Sep 2005 16:41:10 +0200, Takashi Iwai wrote:
> Well, changing the process name in run time is very tricky on Linux. In
> other words: no proper way.

Are you sure? I thought there was a syscall for it.



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Re: Re: Change processname for dmix/dsnoop process

[Takashi Iwai]

At Sun, 02 Oct 2005 00:13:56 +0100,
Mike Hearn wrote:
> 
> On Fri, 30 Sep 2005 16:41:10 +0200, Takashi Iwai wrote:
> > Well, changing the process name in run time is very tricky on Linux. In
> > other words: no proper way.
> 
> Are you sure? I thought there was a syscall for it.

Then I'd be happy to change the code.  Could you give a pointer?


Takashi


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Re: Re: Change processname for dmix/dsnoop process

[Mike Hearn]

Hi David,

Long time no see! If you're ever in England again make sure to drop me a 
line.

Anyway, I remember you showed me a syscall to change the process name - 
do you have a function that could be included in ALSA so the forked dmix 
process can be more obvious?

thanks -mike

Takashi Iwai wrote:

>At Sun, 02 Oct 2005 00:13:56 +0100,
>Mike Hearn wrote:
>  
>
>>On Fri, 30 Sep 2005 16:41:10 +0200, Takashi Iwai wrote:
>>    
>>
>>>Well, changing the process name in run time is very tricky on Linux. In
>>>other words: no proper way.
>>>      
>>>
>>Are you sure? I thought there was a syscall for it.
>>    
>>
>
>Then I'd be happy to change the code.  Could you give a pointer?
>
>
>Takashi
>
>  
>



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Re: Re: Change processname for dmix/dsnoop process

[Mike Hearn]

Actually, I found it - it's SYS_prctl with PR_SET_NAME (2.6 kernels only).

Something like this:

static inline int prctl(int option, unsigned long arg2, unsigned long arg3,
                        unsigned long arg4, unsigned long arg5)
{
    int ret;
    __asm__ __volatile__ ( "pushl %%ebx; movl %2,%%ebx; int $0x80; popl %%ebx"
                           : "=a" (ret) : "0" (SYS_prctl), "r" (option),
                           "c" (arg2), "d" (arg3), "S" (arg4), "D" (arg5) );
    return SYSCALL_RET(ret);
}

prctl(15 /* PR_SET_NAME */, (unsigned long)"dmix", 0, 0, 0);

thanks -mike

Takashi Iwai wrote:

>At Sun, 02 Oct 2005 00:13:56 +0100,
>Mike Hearn wrote:
>  
>
>>On Fri, 30 Sep 2005 16:41:10 +0200, Takashi Iwai wrote:
>>    
>>
>>>Well, changing the process name in run time is very tricky on Linux. In
>>>other words: no proper way.
>>>      
>>>
>>Are you sure? I thought there was a syscall for it.
>>    
>>
>
>Then I'd be happy to change the code.  Could you give a pointer?
>
>
>Takashi
>
>  
>





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Re: Re: Change processname for dmix/dsnoop process

[Takashi Iwai]

At Tue, 04 Oct 2005 15:40:04 +0100,
Mike Hearn wrote:
> 
> Actually, I found it - it's SYS_prctl with PR_SET_NAME (2.6 kernels only).
> 
> Something like this:
> 
> static inline int prctl(int option, unsigned long arg2, unsigned long arg3,
>                         unsigned long arg4, unsigned long arg5)
> {
>     int ret;
>     __asm__ __volatile__ ( "pushl %%ebx; movl %2,%%ebx; int $0x80; popl %%ebx"
>                            : "=a" (ret) : "0" (SYS_prctl), "r" (option),
>                            "c" (arg2), "d" (arg3), "S" (arg4), "D" (arg5) );
>     return SYSCALL_RET(ret);
> }
> 
> prctl(15 /* PR_SET_NAME */, (unsigned long)"dmix", 0, 0, 0);

Great, looks like we have it in sys/prctl.h.
Let's see whether it works...


Thanks,

Takashi


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Re: Re: Change processname for dmix/dsnoop process

[Takashi Iwai]

At Tue, 04 Oct 2005 16:53:37 +0200,
I wrote:
> 
> At Tue, 04 Oct 2005 15:40:04 +0100,
> Mike Hearn wrote:
> > 
> > Actually, I found it - it's SYS_prctl with PR_SET_NAME (2.6 kernels only).
> > 
> > Something like this:
> > 
> > static inline int prctl(int option, unsigned long arg2, unsigned long arg3,
> >                         unsigned long arg4, unsigned long arg5)
> > {
> >     int ret;
> >     __asm__ __volatile__ ( "pushl %%ebx; movl %2,%%ebx; int $0x80; popl %%ebx"
> >                            : "=a" (ret) : "0" (SYS_prctl), "r" (option),
> >                            "c" (arg2), "d" (arg3), "S" (arg4), "D" (arg5) );
> >     return SYSCALL_RET(ret);
> > }
> > 
> > prctl(15 /* PR_SET_NAME */, (unsigned long)"dmix", 0, 0, 0);
> 
> Great, looks like we have it in sys/prctl.h.
> Let's see whether it works...

It seems not always working.  At least, ps shows the old content while
pstree shows the new name.  Possibly because /proc entry doesn't
change.


Takashi


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Re: Re: Change processname for dmix/dsnoop process

[Mike Hearn]

>It seems not always working.  At least, ps shows the old content while
>pstree shows the new name.  Possibly because /proc entry doesn't
>change.
>

Try changing argv[0] before the exec() call - it's got something to do 
with that. I don't remember exactly.


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Re: Re: Change processname for dmix/dsnoop process

[Takashi Iwai]

At Tue, 04 Oct 2005 19:38:05 +0100,
Mike Hearn wrote:
> 
> 
> >It seems not always working.  At least, ps shows the old content while
> >pstree shows the new name.  Possibly because /proc entry doesn't
> >change.
> >
> 
> Try changing argv[0] before the exec() call - it's got something to do 
> with that. I don't remember exactly.

dmix doesn't exec :)
We may overwrite argv[0] string, but its pointer isn't known in the
dmix function.


Takashi


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Re: Re: Change processname for dmix/dsnoop process

[Mike Hearn]

Takashi Iwai wrote:

>dmix doesn't exec :)
>We may overwrite argv[0] string, but its pointer isn't known in the
>dmix function.
>
>  
>
Hmm, IIRC you can get it from the auxiliary array and there is some way 
to get the address of that, but right now I don't remember what it is.


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