[Qemu-devel] Re: [PATCH repost] pci: fix migration device path for devices behind nested bridges

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

The code looks good.
Regarding to the format itself, I don't have strong opinion about it.

What cames into my mind while I'm looking at the code is,
Does BusInfo have to have two path functions? get_dev_path and get_fw_dev_path.
Right now only pci supplies get_dev_path, on the other hand
get_fw_dev_path covers more buses.
This would be another topic, though.

On Fri, Dec 24, 2010 at 10:45:29AM +0200, Michael S. Tsirkin wrote:
> 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.
> 
> Replace this by a hierarchical list of slot/function numbers, walking
> the path from root down to device. Add :00 after the domain number
> so that if there are no nested bridges, this is compatible
> with what we have now.
> 
> Note: as pointed out by Gleb, using openfirmware paths
> might be cleaner, doing this would break compatibility though,
> and the IDs used are not guest or user visible at all,
> so it probably doesn't matter what they are exactly.
> 
> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> ---
> 
> OK I think I'll just apply the below, it seems better for the
> next release than the alternative of disabling migration
> completely, and the IDs used are completely transparent to
> the user, so it probably doesn't matter what they are exactly.
> 
>  hw/pci.c |   44 ++++++++++++++++++++++++++++++++++++--------
>  1 files changed, 36 insertions(+), 8 deletions(-)
> 
> diff --git a/hw/pci.c b/hw/pci.c
> index 8f6fcf8..aed2d42 100644
> --- a/hw/pci.c
> +++ b/hw/pci.c
> @@ -1826,15 +1826,41 @@ 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),
> -             0 /* TODO: need a persistent path for nested buses.
> -                * Note: pci_bus_num(d->bus) is not right as it's guest
> -                * assigned. */,
> -             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.Function:Slot.Function....:Slot.Function.
> +     * 00 is added here to make this format compatible with
> +     * domain:Bus:Slot.Func for systems without nested PCI bridges.
> +     * Slot.Function list specifies the slot and function numbers for all
> +     * devices on the path from root to the specific device. */
> +    int domain_len = strlen("DDDD:00");
> +    int slot_len = strlen(":SS.F");
> +    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 + slot_len * slot_depth;
> +
> +    /* 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:00", pci_find_domain(d->bus));
> +
> +    /* Fill in slot numbers. We walk up from device to root, so need to print
> +     * them in the reverse order, last to first. */
> +    p = path + path_len;
> +    for (t = d; t; t = t->bus->parent_dev) {
> +        p -= slot_len;
> +        snprintf(p, slot_len, ":%02x.%x", PCI_SLOT(t->devfn), PCI_FUNC(d->devfn));
> +    }
> +
> +    return path;
>  }
>  
> -- 
> 1.7.3.2.91.g446ac
> 

-- 
yamahata