[PATCH] pci-assign: Do not reset the device unless the kernel supports it

[Jan Kiszka <jan.kiszka@web.de>]

From: Jan Kiszka <jan.kiszka@siemens.com>

At least kernels 2.6.38 and 2.6.39 do not properly support issuing a
reset on an assigned device and corrupt its config space. Prevent
this by checking for a host kernel with the required support, tagged by
the to-be-introduced KVM_CAP_DEVICE_RESET.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

PS: What's the state of those KVM patches? Will they make it into 3.0?

 hw/device-assignment.c |   33 +++++++++++++++++++--------------
 1 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/hw/device-assignment.c b/hw/device-assignment.c
index 57d8dc0..97a1450 100644
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1689,26 +1689,31 @@ static const VMStateDescription vmstate_assigned_device = {
 static void reset_assigned_device(DeviceState *dev)
 {
     PCIDevice *pci_dev = DO_UPCAST(PCIDevice, qdev, dev);
+#ifdef KVM_CAP_DEVICE_RESET
     AssignedDevice *adev = DO_UPCAST(AssignedDevice, dev, pci_dev);
     char reset_file[64];
     const char reset[] = "1";
     int fd, ret;
 
-    snprintf(reset_file, sizeof(reset_file),
-             "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/reset",
-             adev->host.seg, adev->host.bus, adev->host.dev, adev->host.func);
-
-    /*
-     * Issue a device reset via pci-sysfs.  Note that we use write(2) here
-     * and ignore the return value because some kernels have a bug that
-     * returns 0 rather than bytes written on success, sending us into an
-     * infinite retry loop using other write mechanisms.
-     */
-    fd = open(reset_file, O_WRONLY);
-    if (fd != -1) {
-        ret = write(fd, reset, strlen(reset));
-        close(fd);
+    if (kvm_check_extension(kvm_state, KVM_CAP_DEVICE_RESET) {
+        snprintf(reset_file, sizeof(reset_file),
+                 "/sys/bus/pci/devices/%04x:%02x:%02x.%01x/reset",
+                 adev->host.seg, adev->host.bus, adev->host.dev,
+                 adev->host.func);
+
+        /*
+         * Issue a device reset via pci-sysfs.  Note that we use write(2) here
+         * and ignore the return value because some kernels have a bug that
+         * returns 0 rather than bytes written on success, sending us into an
+         * infinite retry loop using other write mechanisms.
+         */
+        fd = open(reset_file, O_WRONLY);
+        if (fd != -1) {
+            ret = write(fd, reset, strlen(reset));
+            close(fd);
+        }
     }
+#endif /* KVM_CAP_DEVICE_RESET */
 
     /*
      * When a 0 is written to the command register, the device is logically