[PATCH] xc: deal with xen/evtchn and xen/gntdev device names

[Jeremy Fitzhardinge <jeremy@goop.org>]

This patch makes xc_linux properly deal with:
 1. discovering and creating device nodes if necessary
 2. the new form of xen/<dev> device names soon to be used by the kernel

This changes the logic slightly:
 - If a device node already exists with the proper name, then it uses it
   as-is, assuming it has already been correctly created.
 - If the path doesn't exist, or it exists but isn't a device node, and
   it has successfully found the major/minor for the device, then
   (re)create the device node.

Since this logic is identical for gntdev and evtchn, make a common function
to handle both.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>

diff -r f146aa75120c tools/libxc/xc_linux.c
--- a/tools/libxc/xc_linux.c	Thu May 27 12:14:32 2010 -0700
+++ b/tools/libxc/xc_linux.c	Fri May 28 16:33:11 2010 -0700
@@ -378,34 +378,73 @@
     return makedev(major, minor);
 }
 
-#define EVTCHN_DEV_NAME  "/dev/xen/evtchn"
+#define DEVXEN	"/dev/xen"
+
+static int make_dev_xen(void)
+{
+	if (mkdir(DEVXEN, 0755) != 0) {
+		struct stat st;
+
+		if (stat(DEVXEN, &st) != 0 || !S_ISDIR(st.st_mode))
+			return -1;
+	}
+
+	return 0;
+}
+
+static int xendev_open(const char *dev)
+{
+	int fd, devnum;
+	struct stat st;
+	char *devname, *devpath;
+
+	devname = devpath = NULL;
+	fd = -1;
+
+	if (asprintf(&devname, "xen!%s", dev) == 0)
+		goto fail;
+
+	if (asprintf(&devpath, "%s/%s", DEVXEN, dev) == 0)
+		goto fail;
+
+	devnum = xc_find_device_number(dev);
+	if (devnum == -1)
+		devnum = xc_find_device_number(devname);
+
+	/*
+	 * If we know what the correct device is and the path doesn't
+	 * exist or isn't a device, then remove it so we can create the
+	 * device.
+	 */
+	if (devnum != -1 &&
+		(stat(devpath, &st) != 0 || !S_ISCHR(st.st_mode))) {
+		unlink(devpath);
+
+		if (make_dev_xen() == -1)
+			goto fail;
+
+		if (mknod(devpath, S_IFCHR|0600, devnum) != 0) {
+			PERROR("Couldn't make %s",  devpath);
+			goto fail;
+		}
+	}
+
+    fd = open(devpath, O_RDWR);
+
+	if (fd == -1)
+        PERROR("Could not open %s", devpath);
+
+fail:
+	free(devname);
+	free(devpath);
+
+    return fd;
+}
+
 
 int xc_evtchn_open(void)
 {
-    struct stat st;
-    int fd;
-    int devnum;
-
-    devnum = xc_find_device_number("evtchn");
-
-    /* Make sure any existing device file links to correct device. */
-    if ( (lstat(EVTCHN_DEV_NAME, &st) != 0) || !S_ISCHR(st.st_mode) ||
-         (st.st_rdev != devnum) )
-        (void)unlink(EVTCHN_DEV_NAME);
-
- reopen:
-    if ( (fd = open(EVTCHN_DEV_NAME, O_RDWR)) == -1 )
-    {
-        if ( (errno == ENOENT) &&
-             ((mkdir("/dev/xen", 0755) == 0) || (errno == EEXIST)) &&
-             (mknod(EVTCHN_DEV_NAME, S_IFCHR|0600, devnum) == 0) )
-            goto reopen;
-
-        PERROR("Could not open event channel interface");
-        return -1;
-    }
-
-    return fd;
+	return xendev_open("evtchn");
 }
 
 int xc_evtchn_close(int xce_handle)
@@ -519,34 +558,9 @@
     errno = saved_errno;
 }
 
-#define GNTTAB_DEV_NAME "/dev/xen/gntdev"
-
 int xc_gnttab_open(void)
 {
-    struct stat st;
-    int fd;
-    int devnum;
-
-    devnum = xc_find_device_number("gntdev");
-
-    /* Make sure any existing device file links to correct device. */
-    if ( (lstat(GNTTAB_DEV_NAME, &st) != 0) || !S_ISCHR(st.st_mode) ||
-         (st.st_rdev != devnum) )
-        (void)unlink(GNTTAB_DEV_NAME);
-
-reopen:
-    if ( (fd = open(GNTTAB_DEV_NAME, O_RDWR)) == -1 )
-    {
-        if ( (errno == ENOENT) &&
-             ((mkdir("/dev/xen", 0755) == 0) || (errno == EEXIST)) &&
-             (mknod(GNTTAB_DEV_NAME, S_IFCHR|0600, devnum) == 0) )
-            goto reopen;
-
-        PERROR("Could not open grant table interface");
-        return -1;
-    }
-
-    return fd;
+	return xendev_open("gntdev");
 }
 
 int xc_gnttab_close(int xcg_handle)