Re: [Xen-devel] [PATCH V2] libxl: Set path to console on domain startup.

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-12-16 at 12:36 +0000, Ian Jackson wrote:
> Anthony PERARD writes ("Re: [Xen-devel] [PATCH V2] libxl: Set path to console 
> on domain startup."):
> > On Tue, Dec 16, 2014 at 09:30:28AM +0000, Ian Campbell wrote:
> > > Unless by "not running" you meant bottlenecked or not keeping up
> > > perhaps.
> > 
> > Well, I did meant no xenconsoled process. But after, I also tried `kill
> > -STOP`, but the same things is happening.
> 
> I think this is a bug.  I imagine that you can cause `xl create -c' to
> malfunction too.

Presumably the libxl side fix is to register an ev_xswatch (and an
ev_timeout) on the console path (which differs by guest type, see guts
of libxl_console_get_tty) and call the callback out of that instead of
directly at the end of domcreate_....

Depending on how racy this is (not very, I suspect) libvirt could ignore
this possibility and assume the event works (and we'll independently fix
it so it always does), or it could be a bit belt and braces and in
addition to handling the callback also check for NULL and-recheck on the
libvirt internal accessors.

Anthony, you should also note that the callback can happen more than
once, e.g. if you are using pygrub you get it once for the bootloader
pty and then again for the actual guests pty.

Ian.


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