[PATCH] fix nbd driver for 2.5 block layer

This makes NBD work with the new linux 2.5 block layer design.
Specifically, it fixes memory corruption that results from module
removal and possible memory corruption from sending or receiving disk
data from the server.

It essentially rolls together the changes from two of the last patchlets
that I emailed: the fix for module removal & the fix for incorrect
struct bio usage.  I believe it's wisest to roll these both together
into this one patch since they both deal with making NBD work better
with the 2.5 linux block layer design and without either of which, it's
possible that NBD will corrupt memory.

Other changes I'd like to see introduced (like in the earlier jumbo
patch) meanwhile are feature enhancements so they can wait.  This patch
also should address all the very helpful concerns that have been raised
so far.  Particularly:

1. that the very first submitted NBD patch was broken down [Andrew]
2. that only 1 spinlock is used for all the NBD request_queue structures
   used [Jens,Al]
3. that kmap() is used in case of highmem pages [Jens]
4. that the allocation of request_queue is dynamic and seperate from
   other allocated objects [Al]

drivers/block/nbd.c

@@ -28,6 +28,9 @@
  *   the transmit lock. <steve@chygwyn.com>
  * 02-10-11 Allow hung xmit to be aborted via SIGKILL & various fixes.
  *   <Paul.Clements@SteelEye.com> <James.Bottomley@SteelEye.com>
+ * 03-06-22 Make nbd work with new linux 2.5 block layer design. This fixes
+ *   memory corruption from module removal and possible memory corruption
+ *   from sending/receiving disk data. <ldl@aros.net>
  *
  * possible FIXME: make set_sock / set_blksize / set_size / do_it one syscall
  * why not: would need verify_area and friends, would share yet another 
@@ -63,6 +66,16 @@
 
 static struct nbd_device nbd_dev[MAX_NBD];
 
+/*
+ * Use just one lock (or at most 1 per NIC). Two arguments for this:
+ * 1. Each NIC is essentially a synchronization point for all servers
+ *    accessed through that NIC so there's no need to have more locks
+ *    than NICs anyway.
+ * 2. More locks lead to more "Dirty cache line bouncing" which will slow
+ *    down each lock to the point where they're actually slower than just
+ *    a single lock.
+ * Thanks go to Jens Axboe and Al Viro for their LKML emails explaining this!
+ */
 static spinlock_t nbd_lock = SPIN_LOCK_UNLOCKED;
 
 #define DEBUG( s )
@@ -168,6 +181,17 @@ static int nbd_xmit(int send, struct socket *sock, char *buf, int size, int msg_
 	return result;
 }
 
+static inline int sock_send_bvec(struct socket *sock, struct bio_vec *bvec,
+		int flags)
+{
+	int result;
+	void *kaddr = kmap(bvec->bv_page);
+	result = nbd_xmit(1, sock, kaddr + bvec->bv_offset, bvec->bv_len,
+			flags);
+	kunmap(bvec->bv_page);
+	return result;
+}
+
 #define FAIL( s ) { printk( KERN_ERR "NBD: " s "(result %d)\n", result ); goto error_out; }
 
 void nbd_send_req(struct nbd_device *lo, struct request *req)
@@ -209,7 +233,7 @@ void nbd_send_req(struct nbd_device *lo, struct request *req)
 				if ((i < (bio->bi_vcnt - 1)) || bio->bi_next)
 					flags = MSG_MORE;
 				DEBUG("data, ");
-				result = nbd_xmit(1, sock, page_address(bvec->bv_page) + bvec->bv_offset, bvec->bv_len, flags);
+				result = sock_send_bvec(sock, bvec, flags);
 				if (result <= 0)
 					FAIL("Send data failed.");
 			}
@@ -244,6 +268,16 @@ static struct request *nbd_find_request(struct nbd_device *lo, char *handle)
 	return NULL;
 }
 
+static inline int sock_recv_bvec(struct socket *sock, struct bio_vec *bvec)
+{
+	int result;
+	void *kaddr = kmap(bvec->bv_page);
+	result = nbd_xmit(0, sock, kaddr + bvec->bv_offset, bvec->bv_len,
+			MSG_WAITALL);
+	kunmap(bvec->bv_page);
+	return result;
+}
+
 #define HARDFAIL( s ) { printk( KERN_ERR "NBD: " s "(result %d)\n", result ); lo->harderror = result; return NULL; }
 struct request *nbd_read_stat(struct nbd_device *lo)
 		/* NULL returned = something went wrong, inform userspace       */ 
@@ -251,10 +285,11 @@ struct request *nbd_read_stat(struct nbd_device *lo)
 	int result;
 	struct nbd_reply reply;
 	struct request *req;
+	struct socket *sock = lo->sock;
 
 	DEBUG("reading control, ");
 	reply.magic = 0;
-	result = nbd_xmit(0, lo->sock, (char *) &reply, sizeof(reply), MSG_WAITALL);
+	result = nbd_xmit(0, sock, (char *) &reply, sizeof(reply), MSG_WAITALL);
 	if (result <= 0)
 		HARDFAIL("Recv control failed.");
 	req = nbd_find_request(lo, reply.handle);
@@ -268,14 +303,17 @@ struct request *nbd_read_stat(struct nbd_device *lo)
 		FAIL("Other side returned error.");
 
 	if (nbd_cmd(req) == NBD_CMD_READ) {
-		struct bio *bio = req->bio;
+		int i;
+		struct bio *bio;
 		DEBUG("data, ");
-		do {
-			result = nbd_xmit(0, lo->sock, bio_data(bio), bio->bi_size, MSG_WAITALL);
+		rq_for_each_bio(bio, req) {
+			struct bio_vec *bvec;
+			bio_for_each_segment(bvec, bio, i) {
+				result = sock_recv_bvec(sock, bvec);
 				if (result <= 0)
 					HARDFAIL("Recv data failed.");
-			bio = bio->bi_next;
-		} while(bio);
+			}
+		}
 	}
 	DEBUG("done.\n");
 	return req;
@@ -538,8 +576,6 @@ static struct block_device_operations nbd_fops =
  *  (Just smiley confuses emacs :-)
  */
 
-static struct request_queue nbd_queue;
-
 static int __init nbd_init(void)
 {
 	int err = -ENOMEM;
@@ -555,6 +591,17 @@ static int __init nbd_init(void)
 		if (!disk)
 			goto out;
 		nbd_dev[i].disk = disk;
+		/*
+		 * The new linux 2.5 block layer implementation requires
+		 * every gendisk to have its very own request_queue struct.
+		 * These structs are big so we dynamically allocate them.
+		 */
+		disk->queue = kmalloc(sizeof(struct request_queue), GFP_KERNEL);
+		if (!disk->queue) {
+			put_disk(disk);
+			goto out;
+		}
+		blk_init_queue(disk->queue, do_nbd_request, &nbd_lock);
 	}
 
 	if (register_blkdev(NBD_MAJOR, "nbd")) {
@@ -564,7 +611,6 @@ static int __init nbd_init(void)
 #ifdef MODULE
 	printk("nbd: registered device at major %d\n", NBD_MAJOR);
 #endif
-	blk_init_queue(&nbd_queue, do_nbd_request, &nbd_lock);
 	devfs_mk_dir("nbd");
 	for (i = 0; i < MAX_NBD; i++) {
 		struct gendisk *disk = nbd_dev[i].disk;
@@ -582,7 +628,6 @@ static int __init nbd_init(void)
 		disk->first_minor = i;
 		disk->fops = &nbd_fops;
 		disk->private_data = &nbd_dev[i];
-		disk->queue = &nbd_queue;
 		sprintf(disk->disk_name, "nbd%d", i);
 		sprintf(disk->devfs_name, "nbd/%d", i);
 		set_capacity(disk, 0x3ffffe);
@@ -591,8 +636,10 @@ static int __init nbd_init(void)
 
 	return 0;
 out:
-	while (i--)
+	while (i--) {
+		kfree(nbd_dev[i].disk->queue);
 		put_disk(nbd_dev[i].disk);
+	}
 	return err;
 }
 
@@ -600,12 +647,22 @@ static void __exit nbd_cleanup(void)
 {
 	int i;
 	for (i = 0; i < MAX_NBD; i++) {
-		del_gendisk(nbd_dev[i].disk);
-		put_disk(nbd_dev[i].disk);
+		struct gendisk *disk = nbd_dev[i].disk;
+		if (disk) {
+			if (disk->queue) {
+				blk_cleanup_queue(disk->queue);
+				kfree(disk->queue);
+				disk->queue = NULL;
+			}
+			del_gendisk(disk);
+			put_disk(disk);
+		}
 	}
 	devfs_remove("nbd");
-	blk_cleanup_queue(&nbd_queue);
 	unregister_blkdev(NBD_MAJOR, "nbd");
+#ifdef MODULE
+	printk("nbd: unregistered device at major %d\n", NBD_MAJOR);
+#endif
 }
 
 module_init(nbd_init);