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

[Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>]

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).
> 
> >              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.

Ian.

> 
> >                  LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Device Model didn't 
> > respond in time");
> > @@ -874,8 +874,7 @@ static int do_pci_remove(libxl__gc *gc, 
> >                   * SCI, if it doesn't respond in time then we may wish to 
> >                   * force the removal.
> >                   */
> > -                if ( !force )
> > -                    return ERROR_FAIL;
> > +                return ERROR_FAIL;
> >              }
> >          }
> >          path = libxl__sprintf(gc, "/local/domain/0/device-model/%d/state", 
> > domid);
> 
> The more I think about any of this code the worse the idea of the
> "xenstore + wait a bit" API seems, frankly, erroneous.
> 
> Gianni
> 



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