Udev incompatibility with qemu and bochs

Udev incompatibility with qemu and bochs

[Alexander E. Patrakov]

Hello,

udevstart contains the following code:

static void asmlinkage sig_handler(int signum)
{
        switch (signum) {
                case SIGALRM:
                        exit(1);
                case SIGINT:
                case SIGTERM:
                        exit(20 + signum);
        }
}

int main(int argc, char *argv[], char *envp[])
{
/* snip */
        sigaction(SIGALRM, &act, NULL);
        sigaction(SIGINT, &act, NULL);
        sigaction(SIGTERM, &act, NULL);

        /* trigger timeout to prevent hanging processes */
        alarm(UDEV_ALARM_TIMEOUT);
/* snip */
}

UDEV_ALARM_TIMEOUT is defined to 120 seconds in udev.h. The problem is 
that it does take 2 minutes to populate /dev inside slow emulators like 
qemu or bochs, especially when the emulated and host CPU types differ 
and udev rules include RUN+=/sbin/udev_run_hotplugd. The reason is that 
inside those emulators exec() is very expensive (involves 
jit-compilation from one sort of machine code to another). Please 
provide an option to disable this alarm. The preferred form would be an 
environment variable, so that I can type "linux UDEV_NO_ALARM=1" at the 
boot prompt inside the emulator and see the system booting normally.

Thanks,
-- 
Alexander E. Patrakov


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Re: Udev incompatibility with qemu and bochs

[Greg KH]

On Wed, Oct 19, 2005 at 02:39:45PM +0600, Alexander E. Patrakov wrote:
> UDEV_ALARM_TIMEOUT is defined to 120 seconds in udev.h. The problem is 
> that it does take 2 minutes to populate /dev inside slow emulators like 
> qemu or bochs, especially when the emulated and host CPU types differ 
> and udev rules include RUN+=/sbin/udev_run_hotplugd. The reason is that 
> inside those emulators exec() is very expensive (involves 
> jit-compilation from one sort of machine code to another). Please 
> provide an option to disable this alarm. The preferred form would be an 
> environment variable, so that I can type "linux UDEV_NO_ALARM=1" at the 
> boot prompt inside the emulator and see the system booting normally.

Feel free to provide such a patch, if you need it.

thanks,

greg k-h


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Re: Udev incompatibility with qemu and bochs

[Kay Sievers]

On Wed, Oct 19, 2005 at 10:45:55AM -0700, Greg KH wrote:
> On Wed, Oct 19, 2005 at 02:39:45PM +0600, Alexander E. Patrakov wrote:
> > UDEV_ALARM_TIMEOUT is defined to 120 seconds in udev.h. The problem is 
> > that it does take 2 minutes to populate /dev inside slow emulators like 
> > qemu or bochs, especially when the emulated and host CPU types differ 
> > and udev rules include RUN+=/sbin/udev_run_hotplugd. The reason is that 
> > inside those emulators exec() is very expensive (involves 
> > jit-compilation from one sort of machine code to another). Please 
> > provide an option to disable this alarm. The preferred form would be an 
> > environment variable, so that I can type "linux UDEV_NO_ALARM=1" at the 
> > boot prompt inside the emulator and see the system booting normally.
> 
> Feel free to provide such a patch, if you need it.

This timeout is a leftover from the days of tdb, which didn't work well
and caused udev processes to spin around in a corrupted database.

I generally don't like to introduce more facy options to udev and better
set the alarm timeout to a reasonable default or remove it at all.

The problem occurs only on bootup running udevstart, right?
(Depending on your setup 'UDEV_RUN=0 /sbin/udevstart' may be a good
option to speed up the initial population of /dev. Don't know it you
really need to have RUN at that time, depends on how udev is integrated.)

Kay



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Re: Udev incompatibility with qemu and bochs

[Alexander E. Patrakov]

Kay Sievers wrote:

>This timeout is a leftover from the days of tdb, which didn't work well
>and caused udev processes to spin around in a corrupted database.
>
>I generally don't like to introduce more facy options to udev and better
>set the alarm timeout to a reasonable default or remove it at all.
>  
>
Then please remove it.

-- 
Alexander E. Patrakov


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