[libvirt] [PATCH] Read PCI class from sysfs class file instead of config space.

[Thadeu Lima de Souza Cascardo]

When determining if a device is behind a PCI bridge, the PCI device
class is checked by reading the config space. However, there are some
devices which have the wrong class on the config space, but the class is
initialized by Linux correctly as a PCI BRIDGE. This class can be read
by the sysfs file '/sys/bus/pci/devices/xxxx:xx:xx.x/class'.

One example of such bridge is IBM PCI Bridge 1014:03b9, which is
identified as a Host Bridge when reading the config space.

Signed-off-by: Thadeu Lima de Souza Cascardo <casca...@linux.vnet.ibm.com>
---
 src/util/virpci.c |   38 +++++++++++++++++++++++++++++++++++---
 1 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/src/util/virpci.c b/src/util/virpci.c
index 8ec642f..8353411 100644
--- a/src/util/virpci.c
+++ b/src/util/virpci.c
@@ -344,6 +344,34 @@ virPCIDeviceRead32(virPCIDevicePtr dev, int cfgfd, 
unsigned int pos)
 }
 
 static int
+virPCIDeviceReadClass(virPCIDevicePtr dev, uint16_t *device_class)
+{
+    char *path = NULL;
+    char *id_str;
+    int ret = 0;
+    unsigned int value;
+
+    if (virPCIFile(&path, dev->name, "class") < 0)
+        return -1;
+
+    /* class string is '0xNNNNNN\n' ... i.e. 9 bytes */
+    if (virFileReadAll(path, 9, &id_str) < 0) {
+        VIR_FREE(path);
+        return -1;
+    }
+
+    VIR_FREE(path);
+
+    id_str[8] = '\0';
+    ret = virStrToLong_ui(id_str, NULL, 16, &value);
+    if (ret == 0)
+        *device_class = (value >> 8) & 0xFFFF;
+
+    VIR_FREE(id_str);
+    return ret;
+}
+
+static int
 virPCIDeviceWrite(virPCIDevicePtr dev,
                   int cfgfd,
                   unsigned int pos,
@@ -645,8 +673,8 @@ virPCIDeviceIsParent(virPCIDevicePtr dev, virPCIDevicePtr 
check, void *data)
         return 0;
 
     /* Is it a bridge? */
-    device_class = virPCIDeviceRead16(check, fd, PCI_CLASS_DEVICE);
-    if (device_class != PCI_CLASS_BRIDGE_PCI)
+    ret = virPCIDeviceReadClass(check, &device_class);
+    if (ret == -1 || device_class != PCI_CLASS_BRIDGE_PCI)
         goto cleanup;
 
     /* Is it a plane? */
@@ -2110,6 +2138,7 @@ virPCIDeviceDownstreamLacksACS(virPCIDevicePtr dev)
     unsigned int pos;
     int fd;
     int ret = 0;
+    uint16_t device_class;
 
     if ((fd = virPCIDeviceConfigOpen(dev, true)) < 0)
         return -1;
@@ -2119,8 +2148,11 @@ virPCIDeviceDownstreamLacksACS(virPCIDevicePtr dev)
         goto cleanup;
     }
 
+    if (virPCIDeviceReadClass(dev, &device_class))
+        goto cleanup;
+
     pos = dev->pcie_cap_pos;
-    if (!pos || virPCIDeviceRead16(dev, fd, PCI_CLASS_DEVICE) != 
PCI_CLASS_BRIDGE_PCI)
+    if (!pos || device_class != PCI_CLASS_BRIDGE_PCI)
         goto cleanup;
 
     flags = virPCIDeviceRead16(dev, fd, pos + PCI_EXP_FLAGS);
-- 
1.7.1

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