On Mon, Nov 08, 2010 at 07:52:12AM -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 <alex.william...@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? > > Because the device name is not unique. This came about from the > discussion about how to create a canonical device path that Gleb and > Markus are again trying to hash out. If we go up to the bus and get the > bus address, we have a VM unique name. Unfortunately, it's difficult to > define what the bus should print in all cases (ISA), but since they > don't do hotplug and typically don't allocate ramblocks, we can mostly > ignore it for this use case. > > > 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. > > Yes, nested bridges are a problem. How can the seg/bus/devfn not be > unique?
Bus numbers for nested bridges are guest assigned. We start with 0 after reset. > > What does fixing this involve? Just changing pcibus_get_dev_path? > > How do you plan to fix it? Don't forget that migration depends on these > names, so some kind of compatibility layer would be required. Thanks, > > Alex 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. Signed-off-by: Michael S. Tsirkin <m...@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; }