linux-kernel - Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent when reboot

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Date:	Thu, 25 Aug 2011 17:37:32 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Bruno Prémont <bonbons@...ux-vserver.org>
Cc:	Greg Kurz <gkurz@...ibm.com>,
	containers@...ts.linux-foundation.org, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Send a SIGCHLD to the init's pid namespace parent
	when reboot

On 08/24, Bruno Prémont wrote:
>
> On Tue, 23 August 2011 Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > Just in case... instead of WIFSIGNALED/WTERMSIG we can also report
> > the exit code in the upper bits. I mean,
> >
> > 	switch (reboot_cmd) {
> > 	case LINUX_REBOOT_CMD_RESTART:
> > 		code = 1 << 16;
> > 		break;
> > 	case LINUX_REBOOT_CMD_HALT:
> > 		code = 2 << 16;
> > 		break;
> > 	}
>
> That looks nice and simple!

Great. To me, WIFSIGNALED() looks better, but this is subjective and
in any case this is up to you.

> > this can't be confused with the normal exit(code), just the parent
> > should be careful, I am not sure this can't confuse WIFEXITED/WEXITSTATUS
> > user-space macroses.
>
> For recent glibc (2.12.2):
> sys/wait.h and stdlib.h:
> # define WIFEXITED(status) __WIFEXITED (__WAIT_INT (status))
> # define WEXITSTATUS(status)       __WEXITSTATUS (__WAIT_INT (status))
> bits/waitstatus.h:
> #define     __WIFEXITED(status)     (__WTERMSIG(status) == 0)
> #define     __WTERMSIG(status)      ((status) & 0x7f)
> #define     __WEXITSTATUS(status)   (((status) & 0xff00) >> 8)

... and note that __WEXITSTATUS() does "& 0xff00", it uses the
lower 16 bits.

So the parent should read status "by hand". Not a problem, I think.
Say, a traced task reports the additional info this way.

Oleg.

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