Re: [Xen-devel] [PATCH] libxl: do not rely on guest to respond when forcing pci device removal

[Gianni Tedesco <gianni.tedesco@xxxxxxxxxx>]

On Tue, 2011-03-08 at 14:41 +0000, Ian Campbell wrote:
> On Tue, 2011-03-08 at 14:35 +0000, Gianni Tedesco wrote:
> > On Tue, 2011-03-08 at 14:17 +0000, Ian Campbell wrote:
> > > On Tue, 2011-03-08 at 12:56 +0000, Gianni Tedesco wrote:
> > > > On Tue, 2011-03-08 at 11:49 +0000, Ian Campbell wrote:
> > > > > # HG changeset patch
> > > > > # User Ian Campbell <ian.campbell@xxxxxxxxxx>
> > > > > # Date 1299584929 0
> > > > > # Node ID 5084214b8983045d789a86c01e7a0fede46b5e58
> > > > > # Parent  0e3211b5c4da98d170ed665c221bcb00e771fc56
> > > > > libxl: do not rely on guest to respond when forcing pci device removal
> > > > > 
> > > > > This is consistent with the expected semantics of a forced device
> > > > > removal and also avoids a delay when destroying an HVM domain which
> > > > > either does not support hot unplug (does not respond to SCI) or has
> > > > > crashed.
> > > > > 
> > > > > Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> > > > > 
> > > > > diff -r 0e3211b5c4da -r 5084214b8983 tools/libxl/libxl_pci.c
> > > > > --- a/tools/libxl/libxl_pci.c Tue Mar 08 11:13:12 2011 +0000
> > > > > +++ b/tools/libxl/libxl_pci.c Tue Mar 08 11:48:49 2011 +0000
> > > > > @@ -866,7 +866,7 @@ static int do_pci_remove(libxl__gc *gc, 
> > > > >  
> > > > >          /* Remove all functions at once atomically by only signalling
> > > > >           * device-model for function 0 */
> > > > > -        if ( (pcidev->vdevfn & 0x7) == 0 ) {
> > > > > +        if ( !force && (pcidev->vdevfn & 0x7) == 0 ) {
> > > > >              xs_write(ctx->xsh, XBT_NULL, path, "pci-rem", 
> > > > > strlen("pci-rem"));
> > > > 
> > > > Shouldn't we maybe send the pci-rem when force removing to give the
> > > > guest a chance to do something if it can.
> > > 
> > > My concern was just that if this wasn't reacted to by qemu it might
> > > interfere with us sending other requests in the future (I don't know and
> > > haven't checked if that is the case).
> > 
> > It's possible but I think it's unlikely. Generally the qemu hardware
> > emulation works in discrete steps advancing the state machine. The
> > xenstore watching bits work in pretty much the same way.
> > 
> > > > 
> > > > >              if (libxl__wait_for_device_model(ctx, domid, 
> > > > > "pci-removed", NULL, NULL) < 0) {
> > > >                         && !force ) {
> > > > 
> > > > perhaps?
> > > 
> > > Did you mean "!force && libxl__wait..." iow you need the !force to
> > > short-circuit the waiting which was the point of the patch.
> > 
> > No, I meant to do the wait first but just not whinge about it if it
> > times out. But the other way could make sense too, I'll get to that.
> 
> The wait and the timeout are the specific issue I am trying to address.
> When I type "xl destroy foo" I expect domain foo to get shot in the head
> right now, no questions and no hanging around. Similarly if I do "xl
> pci-detach --force...".

OK, fair enough. Honestly, I think my expectation for the detach case to
be more as I stated, but I don't feel strongly about it and it would
just add complexity to have it that way.

Gianni


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