blkfront: module exit handling adjustments

blkdev majors and minor tracking data must be released upon exit, or
else the module can't attach to devices using the same majors upon
being loaded again.

Also replace the literal uses of 202 for the Xen VBD major with the
upstream manifest constant.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/drivers/xen/blkfront/blkfront.c
+++ b/drivers/xen/blkfront/blkfront.c
@@ -962,7 +962,8 @@ module_init(xlblk_init);
 
 static void __exit xlblk_exit(void)
 {
-	return xenbus_unregister_driver(&blkfront_driver);
+	xenbus_unregister_driver(&blkfront_driver);
+	xlbd_release_major_info();
 }
 module_exit(xlblk_exit);
 
--- a/drivers/xen/blkfront/block.h
+++ b/drivers/xen/blkfront/block.h
@@ -156,4 +156,6 @@ static inline void xlvbd_sysfs_delif(str
 }
 #endif
 
+void xlbd_release_major_info(void);
+
 #endif /* __XEN_DRIVERS_BLOCK_H__ */
--- a/drivers/xen/blkfront/vbd.c
+++ b/drivers/xen/blkfront/vbd.c
@@ -40,6 +40,10 @@
 #include <xen/platform-compat.h>
 #endif
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,23)
+#define XENVBD_MAJOR 202
+#endif
+
 #define BLKIF_MAJOR(dev) ((dev)>>8)
 #define BLKIF_MINOR(dev) ((dev) & 0xff)
 
@@ -163,7 +167,7 @@ xlbd_alloc_major_info(int major, int min
 			ptr->type = &xlbd_vbd_type_ext;
 
 		/* 
-		 * if someone already registered block major 202,
+		 * if someone already registered block major XENVBD_MAJOR,
 		 * don't try to register it again
 		 */
 		if (major_info[XLBD_MAJOR_VBD_ALT(index)] != NULL) {
@@ -238,6 +242,32 @@ xlbd_put_major_info(struct xlbd_major_in
 	/* XXX: release major if 0 */
 }
 
+void __exit
+xlbd_release_major_info(void)
+{
+	unsigned int i;
+	int vbd_done = 0;
+
+	for (i = 0; i < ARRAY_SIZE(major_info); ++i) {
+		struct xlbd_major_info *mi = major_info[i];
+
+		if (!mi)
+			continue;
+		if (mi->usage)
+			printk(KERN_WARNING
+			       "vbd: major %u still in use (%u times)\n",
+			       mi->major, mi->usage);
+		if (mi->major != XENVBD_MAJOR || !vbd_done) {
+			unregister_blkdev(mi->major, mi->type->devname);
+			kfree(mi->minors->bitmap);
+			kfree(mi->minors);
+		}
+		if (mi->major == XENVBD_MAJOR)
+			vbd_done = 1;
+		kfree(mi);
+	}
+}
+
 static int
 xlbd_reserve_minors(struct xlbd_major_info *mi, unsigned int minor,
 		    unsigned int nr_minors)
@@ -443,7 +473,7 @@ xlvbd_add(blkif_sector_t capacity, int v
 		minor = BLKIF_MINOR(vdevice);
 	}
 	else {
-		major = 202;
+		major = XENVBD_MAJOR;
 		minor = BLKIF_MINOR_EXT(vdevice);
 	}