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

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

On Mon, Oct 04, 2010 at 03:53:11PM -0600, Alex Williamson wrote:
> pcibus_dev_print() was erroneously retrieving the device bus
> number from the secondary bus number offset of the device
> instead of the bridge above the device.  This ends of landing
> in the 2nd byte of the 3rd BAR for devices, which thankfully
> is usually zero.  pcibus_get_dev_path() copied this code,
> inheriting the same bug.  pcibus_get_dev_path() is used for
> ramblock naming, so changing it can effect migration.  However,
> I've only seen this byte be non-zero for an assigned device,
> which can't migrate anyway, so hopefully we won't run into
> any issues.
> 
> Signed-off-by: Alex Williamson <alex.williamson@redhat.com>

Good catch. Applied.
I don't really see why do we put the dev path
in the bus object: why not let device supply its name?

And I think this will affect nested bridges. However they are currently
broken anyway: we really must convert to topological names as bus number
is guest-assigned - they don't have to be unique, even.

What does fixing this involve? Just changing pcibus_get_dev_path?

> ---
> 
>  hw/pci.c |    5 ++---
>  1 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 6d0934d..15416dd 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -1940,8 +1940,7 @@ static void pcibus_dev_print(Monitor *mon, DeviceState *dev, int indent)
>  
>      monitor_printf(mon, "%*sclass %s, addr %02x:%02x.%x, "
>                     "pci id %04x:%04x (sub %04x:%04x)\n",
> -                   indent, "", ctxt,
> -                   d->config[PCI_SECONDARY_BUS],
> +                   indent, "", ctxt, pci_bus_num(d->bus),
>                     PCI_SLOT(d->devfn), PCI_FUNC(d->devfn),
>                     pci_get_word(d->config + PCI_VENDOR_ID),
>                     pci_get_word(d->config + PCI_DEVICE_ID),
> @@ -1965,7 +1964,7 @@ static char *pcibus_get_dev_path(DeviceState *dev)
>      char path[16];
>  
>      snprintf(path, sizeof(path), "%04x:%02x:%02x.%x",
> -             pci_find_domain(d->bus), d->config[PCI_SECONDARY_BUS],
> +             pci_find_domain(d->bus), pci_bus_num(d->bus),
>               PCI_SLOT(d->devfn), PCI_FUNC(d->devfn));
>  
>      return strdup(path);
>