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

[Michael S. Tsirkin]

On Mon, Dec 13, 2010 at 01:04:23PM -0700, Alex Williamson wrote:
> On Mon, 2010-11-08 at 13:22 +0200, Michael S. Tsirkin wrote:
> > 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 <address@hidden>
> > 
> > Good catch. Applied.
> 
> Um... submitted vs applied:
> 
>      PCI: Bus number from the bridge, not the device
>  
> @@ -6,20 +8,28 @@
>      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,
> +    is usually zero.
> +    
> +    Note: 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.
>  
> +    This patch does not touch pcibus_get_dev_path, as
> +    bus number is guest assigned for nested buses,
> +    so using it for migration is broken anyway.
> +    Fix it properly later.
> +    
>      Signed-off-by: Alex Williamson <address@hidden>
> +    Signed-off-by: Michael S. Tsirkin <address@hidden>
>  
>  diff --git a/hw/pci.c b/hw/pci.c
> -index 6d0934d..15416dd 100644
> +index 962886e..8f6fcf8 100644
>  --- a/hw/pci.c
>  +++ b/hw/pci.c
> -@@ -1940,8 +1940,7 @@ static void pcibus_dev_print(Monitor *mon, DeviceState 
> *dev, int indent)
> +@@ -1806,8 +1806,7 @@ 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",
> @@ -29,14 +39,3 @@
>                      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);
> -
> -
> 
> So the chunk that fixed the part that I was actually interested in got
> dropped even though the existing code is clearly wrong.  Yes, we still
> have issues with nested bridges (not that we have many of those), but
> until the "Fix it properly later" part comes along, can we please
> include the obvious bug fix?  Thanks,
> 
> Alex

We can stick 0 in there - would that help?  I would much rather not
create a version where we put the bus number there.

-- 
MST