[lxc-devel] [PATCH] exclude non-existing signals from the loop

[Michael H. Warfield]

On Fri, 2014-01-17 at 08:24 -0600, Serge Hallyn wrote: 
> Quoting Qiang Huang (h.huangqiang at huawei.com):
> > On 2014/1/17 5:38, Serge Hallyn wrote:
> > > Quoting S.Çağlar Onur (caglar at 10ur.org):
> > >> On Thu, Jan 16, 2014 at 4:24 PM, Serge Hallyn <serge.hallyn at ubuntu.com> wrote:
> > >>> Quoting S.Çağlar Onur (caglar at 10ur.org):
> > >>>> 32 and 33 are not defined and causing sigaction to fail. "kill -l" shows following
> > >>>> on my system
> > >>>>
> > >>>>  1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL       5) SIGTRAP
> > >>>>  6) SIGABRT      7) SIGBUS       8) SIGFPE       9) SIGKILL     10) SIGUSR1
> > >>>> 11) SIGSEGV     12) SIGUSR2     13) SIGPIPE     14) SIGALRM     15) SIGTERM
> > >>>> 16) SIGSTKFLT   17) SIGCHLD     18) SIGCONT     19) SIGSTOP     20) SIGTSTP
> > >>>> 21) SIGTTIN     22) SIGTTOU     23) SIGURG      24) SIGXCPU     25) SIGXFSZ
> > >>>> 26) SIGVTALRM   27) SIGPROF     28) SIGWINCH    29) SIGIO       30) SIGPWR
> > >>>> 31) SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3
> > >>>> 38) SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
> > >>>> 43) SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
> > >>>> 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
> > >>>> 53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9  56) SIGRTMAX-8  57) SIGRTMAX-7
> > >>>> 58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4  61) SIGRTMAX-3  62) SIGRTMAX-2
> > >>>> 63) SIGRTMAX-1  64) SIGRTMAX
> > >>>>
> > >>>> Signed-off-by: S.Çağlar Onur <caglar at 10ur.org>
> > >>>
> > >>> Odd...  on my system NSIG is 32, so these should never hit (since it is
> > >>> in a while i<NSIG loop)
> > >>
> > >> Printing NSIG via ERROR shows that its 64 on my system.
> > > 
> > > So a header file is #defining NSIG, which is already defined to 32
> > > in kernel headers, to _NSIG, which is 64.
> > > 
> > > Looking around the current state of kernel headers, i wonder whether
> > > we should imply use min(SIGRTMIN, NSIG).
> > 
> > My box is x86_64, and I got the same result as S.Çağlar.
> > 
> > People may use signal number bigger than SIGRTMIN, so min(SIGRTMIN, NSIG)
> > would miss them. Isn't that cause any problems?
> > 
> > Maybe we should just bypass there non-existent signals.
> 
> If we could know on any system which signals to bypass that'd be
> fine, but AFAICS we can't.

> It sounds to me like we should simply ignore failure at sigaction like
> we used to :)  Something like below.  Is that what you meant?

That would make the most sense to me.

What would be the downside to ignoring the failure?  Are there any error
condition which we should not ignore?

The man page indicates that errno has two defined values on failure.
Either EINVAL, meaning an invalid signal was specified and we SHOULD
ignore it, or EFAULT indicating something wrong with the pointers passed
to it, which indicates something seriously wrong in the code.  That
doesn't mean there might not be others that they didn't think to
list...  :-P

> From 87319b691c8f65c7d61ee01e64707d0b59d11caa Mon Sep 17 00:00:00 2001
> From: Serge Hallyn <serge.hallyn at ubuntu.com>
> Date: Fri, 17 Jan 2014 08:23:18 -0600
> Subject: [PATCH 1/1] lxc_init: don't fail on bad signals
> 
> Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
> ---
>  src/lxc/lxc_init.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/src/lxc/lxc_init.c b/src/lxc/lxc_init.c
> index a59dd9c..b86edf8 100644
> --- a/src/lxc/lxc_init.c
> +++ b/src/lxc/lxc_init.c
> @@ -159,8 +159,7 @@ int main(int argc, char *argv[])
>  		act.sa_flags = 0;
>  		act.sa_handler = interrupt_handler;
>  		if (sigaction(i, &act, NULL)) {
> -			SYSERROR("failed to sigaction");
> -			exit(EXIT_FAILURE);
> +			INFO ("failed to sigaction (%d)", i);
>  		}
>  	}
>  
> -- 
> 1.8.5.2
> 
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-- 
Michael H. Warfield (AI4NB) | (770) 978-7061 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!

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