Re: [Qemu-devel] Re: [PATCH] PCI: Bus number from the bridge, not the device

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 09, 2010 at 11:41:43AM +0900, Isaku Yamahata wrote:
> On Mon, Nov 08, 2010 at 06:26:33PM +0200, Michael S. Tsirkin wrote:
> > Replace bus number with slot numbers of parent bridges up to the root.
> > This works for root bridge in a compatible way because bus number there
> > is hard-coded to 0.
> > IMO nested bridges are broken anyway, no way to be compatible there.
> > 
> > 
> > Gleb, Markus, I think the following should be sufficient for PCI.  What
> > do you think?  Also - do we need to update QMP/monitor to teach them to
> > work with these paths?
> > 
> > This is on top of Alex's patch, completely untested.
> > 
> > 
> > pci: fix device path for devices behind nested bridges
> > 
> > We were using bus number in the device path, which is clearly
> > broken as this number is guest-assigned for all devices
> > except the root.
> > 
> > Fix by using hierarchical list of slots, walking the path
> > from root down to device, instead. Add :00 as bus number
> > so that if there are no nested bridges, this is compatible
> > with what we have now.
> 
> This format, Domain:00:Slot:Slot....:Slot.Function, doesn't work
> because pci-to-pci bridge is pci function.
> So the format should be
> Domain:00:Slot.Function:Slot.Function....:Slot.Function
> 
> thanks,

Hmm, interesting. If we do this we aren't backwards compatible
though, so maybe we could try using openfirmware paths, just as well.

> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > 
> > diff --git a/hw/pci.c b/hw/pci.c
> > index 7d12473..fa98d94 100644
> > --- a/hw/pci.c
> > +++ b/hw/pci.c
> > @@ -1826,13 +1826,45 @@ static void pcibus_dev_print(Monitor *mon, DeviceState *dev, int indent)
> >  
> >  static char *pcibus_get_dev_path(DeviceState *dev)
> >  {
> > -    PCIDevice *d = (PCIDevice *)dev;
> > -    char path[16];
> > -
> > -    snprintf(path, sizeof(path), "%04x:%02x:%02x.%x",
> > -             pci_find_domain(d->bus), pci_bus_num(d->bus),
> > -             PCI_SLOT(d->devfn), PCI_FUNC(d->devfn));
> > -
> > -    return strdup(path);
> > +    PCIDevice *d = container_of(dev, PCIDevice, qdev);
> > +    PCIDevice *t;
> > +    int slot_depth;
> > +    /* Path format: Domain:00:Slot:Slot....:Slot.Function.
> > +     * 00 is added here to make this format compatible with
> > +     * domain:Bus:Slot.Func for systems without nested PCI bridges.
> > +     * Slot list specifies the slot numbers for all devices on the
> > +     * path from root to the specific device. */
> > +    int domain_len = strlen("DDDD:00");
> > +    int func_len = strlen(".F");
> > +    int slot_len = strlen(":SS");
> > +    int path_len;
> > +    char *path, *p;
> > +
> > +    /* Calculate # of slots on path between device and root. */;
> > +    slot_depth = 0;
> > +    for (t = d; t; t = t->bus->parent_dev)
> > +        ++slot_depth;
> > +
> > +    path_len = domain_len + bus_len + slot_len * slot_depth + func_len;
> > +
> > +    /* Allocate memory, fill in the terminating null byte. */
> > +    path = malloc(path_len + 1 /* For '\0' */);
> > +    path[path_len] = '\0';
> > +
> > +    /* First field is the domain. */
> > +    snprintf(path, domain_len, "%04x", pci_find_domain(d->bus));
> > +
> > +    /* Leave space for slot numbers and fill in function number. */
> > +    p = path + domain_len + slot_len * slot_depth;
> > +    snprintf(p, func_len, ".%02x", PCI_FUNC(d->devfn));
> > +
> > +    /* Fill in slot numbers. We walk up from device to root, so need to print
> > +     * them in the reverse order, last to first. */
> > +    for (t = d; t; t = t->bus->parent_dev) {
> > +        p -= slot_len;
> > +        snprintf(p, slot_len, ":%x", PCI_SLOT(t->devfn));
> > +    }
> > +
> > +    return path;
> >  }
> >  
> > 
> 
> -- 
> yamahata