[PATCH] nbd: Don't create all MAX_NBD devices by default all the time

This patches adds the "nbds_max" parameter to the nbd kernel module, which
limits the number of nbds allocated.  Previously, always all 128 entries
were allocated unconditionally, which used to waste resources and
needlessly flood the hotplug system with events.  (Defaults to 16 now.)
Signed-off-by: Lars Marowsky-Bree <lmb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/block/nbd.c

@@ -78,6 +78,7 @@
 #define DBG_RX          0x0200
 #define DBG_TX          0x0400
 static unsigned int debugflags;
+static unsigned int nbds_max = 16;
 #endif /* NDEBUG */
 
 static struct nbd_device nbd_dev[MAX_NBD];
@@ -647,7 +648,13 @@ static int __init nbd_init(void)
 		return -EIO;
 	}
 
-	for (i = 0; i < MAX_NBD; i++) {
+	if (nbds_max > MAX_NBD) {
+		printk(KERN_CRIT "nbd: cannot allocate more than %u nbds; %u requested.\n", MAX_NBD,
+				nbds_max);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < nbds_max; i++) {
 		struct gendisk *disk = alloc_disk(1);
 		if (!disk)
 			goto out;
@@ -673,7 +680,7 @@ static int __init nbd_init(void)
 	dprintk(DBG_INIT, "nbd: debugflags=0x%x\n", debugflags);
 
 	devfs_mk_dir("nbd");
-	for (i = 0; i < MAX_NBD; i++) {
+	for (i = 0; i < nbds_max; i++) {
 		struct gendisk *disk = nbd_dev[i].disk;
 		nbd_dev[i].file = NULL;
 		nbd_dev[i].magic = LO_MAGIC;
@@ -706,8 +713,9 @@ out:
 static void __exit nbd_cleanup(void)
 {
 	int i;
-	for (i = 0; i < MAX_NBD; i++) {
+	for (i = 0; i < nbds_max; i++) {
 		struct gendisk *disk = nbd_dev[i].disk;
+		nbd_dev[i].magic = 0;
 		if (disk) {
 			del_gendisk(disk);
 			blk_cleanup_queue(disk->queue);
@@ -725,6 +733,8 @@ module_exit(nbd_cleanup);
 MODULE_DESCRIPTION("Network Block Device");
 MODULE_LICENSE("GPL");
 
+module_param(nbds_max, int, 0444);
+MODULE_PARM_DESC(nbds_max, "How many network block devices to initialize.");
 #ifndef NDEBUG
 module_param(debugflags, int, 0644);
 MODULE_PARM_DESC(debugflags, "flags for controlling debug output");