[libvirt] [Xen-devel] [PATCH 00/12] libxl: fork: SIGCHLD flexibility

Jim Fehlig jfehlig at suse.com
Thu Jan 30 16:14:01 UTC 2014

Daniel P. Berrange wrote:
> On Mon, Jan 27, 2014 at 06:39:36PM -0700, Jim Fehlig wrote:
>> [Adding libvirt list...]
>> Ian Jackson wrote:
>>> Jim Fehlig writes ("Re: [Xen-devel] [PATCH 00/12] libxl: fork: SIGCHLD flexibility"):
> BTW, I meant to ask before - what is the SIGCHLD reference about in the
> subject line ?

This is related to child processes started by libxl.  E.g. running a
bootloader when creating PV VMs, running a save/restore helper when
saving/restoring a VM, etc.

> libvirt drivers that live inside libvirtd should never use or rely on
> the SIGCHLD signal at all. All VM processes started by libvirtd ought
> to be fully daemonized so that their parent is pid 1 / init. This ensures
> that the libvirtd daemon can be restarted without all the VMs getting
> reaped. Once the VMs are reparented to init, then libvirt or library
> code it uses has no way of ever receiving SIGCHLD.

Nod.  VMs are "daemonized", in the context of Xen.  Once running,
libvirtd can be restarted without reaping them.


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