[Qemu-devel] [Patch] Auto-detect USB devfs in Linux

[TJ <linux@tjworld.net>]

Since Linux kernel 2.6.14 the USB device file-system has moved from
'/proc/bus/usb' to '/dev/bus/usb' but qemu has '/proc/bus/usb'
hard-coded in usb-linux.c

I explored the option of moving USBDEVFS_PATH to config.h but it would
require several additions to the configure script as well as the changes
to usb-linux.c

Therefore I have opted to detect which USB file-system is in use by
extending the error-detection in usb_host_scan() to first try 
'/dev/bus/usb' and if that fails, then try the pre-2.6.14
'/proc/bus/usb'.

The new code uses a (new) static char 'usb_devfs_path' set to the path
that works, and it is subsequently used in usb_host_device_open().

TJ.

Index: usb-linux.c
===================================================================
RCS file: /sources/qemu/qemu/usb-linux.c,v
retrieving revision 1.15
diff -u -r1.15 usb-linux.c
--- usb-linux.c	31 Oct 2007 00:27:50 -0000	1.15
+++ usb-linux.c	2 Nov 2007 11:31:57 -0000
@@ -52,7 +52,17 @@
 //#define DEBUG_ISOCH
 //#define USE_ASYNCIO
 
-#define USBDEVFS_PATH "/proc/bus/usb"
+/*
+ * TJ <linux@tjworld.net> 2007-11-02
+ * Now defaults to /dev/bus/usb/devices which was introduced into kernel version 2.6.14 with 
+ * commit fbf82fd2e1f4e679c60516d772d1862c941ca845 on Jul 31st 2005.
+ * 
+ * If the 'devices' file doesn't exist, code checks for the older "/proc/bus/usb/devices"
+ * before reporting an error.
+*/
+static unsigned char usb_devfs_path[64];
+#define USB_DEVFS_PATH_PRE_2_6_14 "/proc/bus/usb"
+#define USB_DEVFS_PATH "/dev/bus/usb"
 #define PRODUCT_NAME_SZ 32
 #define SIG_ISOCOMPLETE (SIGRTMIN+7)
 #define MAX_ENDPOINTS 16
@@ -614,7 +624,7 @@
                              devname) < 0)
         return NULL;
 
-    snprintf(buf, sizeof(buf), USBDEVFS_PATH "/%03d/%03d",
+    snprintf(buf, sizeof(buf), "%s/%03d/%03d", usb_devfs_path,
              bus_num, addr);
     fd = open(buf, O_RDWR | O_NONBLOCK);
     if (fd < 0) {
@@ -737,11 +747,25 @@
     int bus_num, addr, speed, device_count, class_id, product_id, vendor_id;
     int ret;
     char product_name[512];
-
-    f = fopen(USBDEVFS_PATH "/devices", "r");
+    
+    /* TJ <linux@tjworld.net> 2007-11-02
+     * Auto-detect USB devices file-system location
+     * pre 2.6.14 kernels used /proc/bus/usb
+     * Standard location is now /dev/bus/usb
+     * Retain correct location in static variable for use by usb_host_device_open()
+     */
+    snprintf(usb_devfs_path, sizeof(usb_devfs_path), "%s", USB_DEVFS_PATH);
+    /* use buf temporarily to build path to devices file */
+    snprintf(buf, sizeof(buf), "%s/devices", usb_devfs_path);
+    f = fopen(buf, "r");
     if (!f) {
-        term_printf("Could not open %s\n", USBDEVFS_PATH "/devices");
-        return 0;
+        snprintf(usb_devfs_path, sizeof(usb_devfs_path), "%s", USB_DEVFS_PATH_PRE_2_6_14);
+        snprintf(buf, sizeof(buf), "%s/devices", usb_devfs_path);
+        f = fopen(buf, "r");
+        if (!f) {
+            term_printf("Could not open USB devices file %s\n", buf);
+            return 0;
+        }
     }
     device_count = 0;
     bus_num = addr = speed = class_id = product_id = vendor_id = 0;