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

[Michael S. Tsirkin]

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 slot/function numbers, 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.

Note: as pointed out by Gleb, using openfirmware paths
might be cleaner, doing this would break compatibility though.

Signed-off-by: Michael S. Tsirkin <address@hidden>
---

So this fixes the issue with bridges at function != 0.
Untested.

An alternative that will still preserve compatibility
is to do something like
        if (domain || d->bus->parent_device) {
                use OF path
        } else {
            snprintf(path, sizeof(path), "0000:00:%02x.%x",
                     PCI_SLOT(d->devfn), PCI_FUNC(d->devfn));
        }

Would that be better?
Please comment.

 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
@@ -1826,13 +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), d->config[PCI_SECONDARY_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.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", 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