On Fri, Feb 14, 2020 at 03:00:34PM +0100, Marc-André Lureau wrote: > Hi > > On Fri, Feb 14, 2020 at 2:24 PM Boeuf, Sebastien > <sebastien.bo...@intel.com> wrote: > > > > Hi Marc-Andre, > > > > On Tue, 2020-02-11 at 22:24 +0100, Marc-André Lureau wrote: > > > Hi > > > > > > On Tue, Feb 11, 2020 at 4:24 PM Boeuf, Sebastien > > > <sebastien.bo...@intel.com> wrote: > > > > From c073d528b8cd7082832fd1825dc33dd65b305aa2 Mon Sep 17 00:00:00 > > > > 2001 > > > > From: Sebastien Boeuf <sebastien.bo...@intel.com> > > > > Date: Tue, 11 Feb 2020 16:01:22 +0100 > > > > Subject: [PATCH] docs: Update vhost-user spec regarding backend > > > > program > > > > conventions > > > > > > > > The vhost-user specification is not clearly stating the expected > > > > behavior from a backend program whenever the client disconnects. > > > > > > > > This patch addresses the issue by defining the default behavior and > > > > proposing an alternative through a command line option. > > > > > > > > By default, a backend program will have to keep listening even if > > > > the > > > > client disconnects, unless told otherwise through the newly > > > > introduced > > > > option --exit-on-disconnect. > > > > > > > > Signed-off-by: Sebastien Boeuf <sebastien.bo...@intel.com> > > > > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com> > > > > --- > > > > docs/interop/vhost-user.rst | 10 ++++++++++ > > > > 1 file changed, 10 insertions(+) > > > > > > > > diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost- > > > > user.rst > > > > index 5f8b3a456b..da9a1ebc4c 100644 > > > > --- a/docs/interop/vhost-user.rst > > > > +++ b/docs/interop/vhost-user.rst > > > > @@ -1323,6 +1323,10 @@ The backend program must end (as quickly and > > > > cleanly as possible) when > > > > the SIGTERM signal is received. Eventually, it may receive SIGKILL > > > > by > > > > the management layer after a few seconds. > > > > > > > > +By default, the backend program continues running after the client > > > > +disconnects. It accepts only 1 connection at a time on each UNIX > > > > domain > > > > +socket. > > > > > > I don't think that's the most common behaviour. libvhost-user will > > > panic() on disconnect in general, unless the error/exit is handled > > > gracefully by the backend. > > > > It's not the default behavior from libvhost-user, but that's exactly > > something I'd like to see changing. This should be the normal case if > > you think about a standard client/server connection, where the server > > would simply listen again after the client disconnects. > > I disagree, a "normal" lifecycle is a single connection & instance per device. > > Having the backend handle multiple connections is needlessly more > complicated. You need to correctly handle multiple states, flushed > anything private between connections etc. It should be optional. > > > > > > > > The most common case is to have 1-1 relation between device/qemu > > > instance and backend. > > > > Yes this part is fine, but that's not a reason why the backend should > > terminates. > > It is simpler to ensure it is reset correctly. > > > > > > > > > Why not restart the backend for another instance? > > > > Because you need some management tool to do so. And I think that by > > default it could be interesting to have the least amount of extra > > management involved. > > The management layer should be involved if any side crashes or restart anyway.
Further, this vhost-user.rst spec document is explicitly describing the contract between the vhost-user binaries and the management layer. So it doesn't make sense to say update this doc to describe desired semantics for usage /without/ a management layer. So I agree, the default behaviour should be that there is one binary spawned at time the associated device is initialization, and that the lifetime of the binary is 1:1 associated with the lifetime of the VM, or until the device is unplugged. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
