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

[Isaku Yamahata <yamahata@valinux.co.jp>]

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,

> 
> 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