[Qemu-devel] Re: [REASON][PATCH-REQUEST] Starting QEMU by PHP/Apache

["Bolle" <bolle@geodb.org>]

After some research, I think that Apache with mod_php is 
blocking the SIGALRM.

This is not the fault of QEMU. But maybe, QEMU could check 
on the start-up, if SIGALRM is enabled and usable. If not, 
then it can bail out and inform the user about this.

I believe, there are other environments where SIGALRM is 
blocked too.

Andreas

PS: Sorry for not being able to provide a patch by my 
self.


On Wed, 14 Oct 2009 07:12:56 +0200
  "Bolle" <bolle@geodb.org> wrote:
> Hello all
> 
>First, I forgot to say, that I use the QEMU stable 
>version 11.0 on a Gentoo box. I did some more testings. 
>The QEMU instance is starting and sometimes the OS starts 
>to load, but then QEMU stucks and consumes 100% CPU.
> 
> I checked the startup it with strace. The start of QEMU 
>itself produces the same output in strace, regardless if 
>started by the PHP CLI or by mod_php from Apache.
> 
> I then attached strace to the QEMU process, and there is 
>a big difference.
> 
> When starting QEMU with the PHP script from the CLI (as 
>the same user as the web server), it works and I get 
>something like that:
> ...
> select(12, [6 11], [], [], {4, 993369}) = ? 
>ERESTARTNOHAND (To be restarted)
> --- SIGALRM (Alarm clock) @ 0 (0) ---
> write(7, "\0"..., 1)                    = 1
> sigreturn()                             = ? (mask now 
>[])
> clock_gettime(CLOCK_MONOTONIC, {2818001, 146485529}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2818001, 146548886}) = 0
> timer_gettime(0, {it_interval={0, 0}, it_value={0, 0}}) 
>= 0
> timer_settime(0, 0, {it_interval={0, 0}, it_value={0, 
>250000}}, NULL) = 0
> clock_gettime(CLOCK_MONOTONIC, {2818001, 146758750}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2818001, 146819115}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2818001, 146879549}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2818001, 146938839}) = 0
> --- SIGALRM (Alarm clock) @ 0 (0) ---
> write(7, "\0"..., 1)                    = 1
> sigreturn()                             = ? (mask now 
>[])
> ...
> 
> If QEMU has been started by the web server with the same 
>script and user, I get:
> ...
> select(11, [5 10], [], [], {3, 767239}) = 0 (Timeout)
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818297714}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818382772}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818444894}) = 0
> timer_gettime(0, {it_interval={0, 0}, it_value={0, 0}}) 
>= 0
> timer_settime(0, 0, {it_interval={0, 0}, it_value={0, 
>250000}}, NULL) = 0
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818698197}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818759263}) = 0
> timer_gettime(0, {it_interval={0, 0}, it_value={0, 
>67453}}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818894002}) = 0
> clock_gettime(CLOCK_MONOTONIC, {2817617, 818954673}) = 0
> timer_gettime(0, {it_interval={0, 0}, it_value={0, 0}}) 
>= 0
> timer_settime(0, 0, {it_interval={0, 0}, it_value={0, 
>250000}}, NULL) = 0
> ...
> 
> There are no SIGALRM executed. What can be the reason 
>for that ?
> 
> Andreas