Prefer sysfs for USB host devices

Scanning for devices via /sys/bus/usb/devices/ and using them via the
/dev/bus/usb/<bus>/<device> character devices is the prefered method
on modern kernels, so try that first.

When using SELinux and libvirt, qemu will have access to /sys/bus/usb
but not /proc/bus/usb, so although the current code will work just
fine, it will generate SELinux AVC warnings.

See also:

  https://bugzilla.redhat.com/508326

Reported-by: Daniel Berrange <berrange@redhat.com>
Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 9 insertions, 9 deletions

diff --git a/usb-linux.c b/usb-linux.c
index 67e4acd..3c724ba 100644
--- a/usb-linux.c
+++ b/usb-linux.c
@@ -1265,6 +1265,15 @@ static int usb_host_scan(void *opaque, USBScanFunc *func)
 
     /* only check the host once */
     if (!usb_fs_type) {
+        dir = opendir(USBSYSBUS_PATH "/devices");
+        if (dir) {
+            /* devices found in /dev/bus/usb/ (yes - not a mistake!) */
+            strcpy(devpath, USBDEVBUS_PATH);
+            usb_fs_type = USB_FS_SYS;
+            closedir(dir);
+            dprintf(USBDBG_DEVOPENED, USBSYSBUS_PATH);
+            goto found_devices;
+        }
         f = fopen(USBPROCBUS_PATH "/devices", "r");
         if (f) {
             /* devices found in /proc/bus/usb/ */
@@ -1284,15 +1293,6 @@ static int usb_host_scan(void *opaque, USBScanFunc *func)
             dprintf(USBDBG_DEVOPENED, USBDEVBUS_PATH);
             goto found_devices;
         }
-        dir = opendir(USBSYSBUS_PATH "/devices");
-        if (dir) {
-            /* devices found in /dev/bus/usb/ (yes - not a mistake!) */
-            strcpy(devpath, USBDEVBUS_PATH);
-            usb_fs_type = USB_FS_SYS;
-            closedir(dir);
-            dprintf(USBDBG_DEVOPENED, USBSYSBUS_PATH);
-            goto found_devices;
-        }
     found_devices:
         if (!usb_fs_type) {
             monitor_printf(mon, "husb: unable to access USB devices\n");