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Re: [Libvir] [PATCH] lxc: handle SIGCHLD from exiting container



On Wed, Apr 30, 2008 at 11:38:01PM -0700, Dave Leskovec wrote:
> This patch allows the lxc driver to handle SIGCHLD signals from exiting
> containers.  The handling will perform some cleanup such as waiting for
> the container process and killing/waiting the tty process.  This is also
> required as a first step towards providing some kind of client container exit
> notification.  Additional support is needed for that but this SIGCHLD handling
> is what would trigger the notification.
> 
> libvirtd was already catching SIGCHLD although it was just ignoring it.  I
> implemented a mechanism to distribute the signal to any other drivers in the
> daemon that registered a function to handle them.  This required some changes to
> the way libvirtd was catching signals (to get the pid of the sending process) as
> well as an addition to the state driver structure.  The intent was to provide
> future drivers access to signals as well.

The reason it was ignoring it was because the QEMU driver detects the
shutdown of the VM without using the SIGCHLD directly. It instead detects
EOF on the STDOUT/ERR of the VM child process & calls waitpid() then to
cleanup.  I notice that the LXC driver does not appear to setup any
STDERR/OUT for its VMs so they're still inheriting the daemon's. If it
isn't a huge problem it'd be desirable to try & have QEMU & LXC operate
in the same general way wrt to their primary child procs for VMs. 

Regards,
Daniel.
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