nbd: correct disconnect behavior

commit c378f70a upstream.

Currently, when a disconnect is requested by the user (via NBD_DISCONNECT
ioctl) the return from NBD_DO_IT is undefined (it is usually one of
several error codes).  This means that nbd-client does not know if a
manual disconnect was performed or whether a network error occurred.
Because of this, nbd-client's persist mode (which tries to reconnect after
error, but not after manual disconnect) does not always work correctly.

This change fixes this by causing NBD_DO_IT to always return 0 if a user
requests a disconnect.  This means that nbd-client can correctly either
persist the connection (if an error occurred) or disconnect (if the user
requested it).
Signed-off-by: Paul Clements <paul.clements@steeleye.com>
Acked-by: Rob Landley <rob@landley.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[bwh: Backported to 3.2: adjust device pointer name]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/block/nbd.c

@@ -598,8 +598,10 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
 		if (!lo->sock)
 			return -EINVAL;
 
+		lo->disconnect = 1;
+
 		nbd_send_req(lo, &sreq);
-                return 0;
+		return 0;
 	}
  
 	case NBD_CLEAR_SOCK: {
@@ -629,6 +631,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
 				lo->sock = SOCKET_I(inode);
 				if (max_part > 0)
 					bdev->bd_invalidated = 1;
+				lo->disconnect = 0; /* we're connected now */
 				return 0;
 			} else {
 				fput(file);
@@ -701,6 +704,8 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *lo,
 		set_capacity(lo->disk, 0);
 		if (max_part > 0)
 			ioctl_by_bdev(bdev, BLKRRPART, 0);
+		if (lo->disconnect) /* user requested, ignore socket errors */
+			return 0;
 		return lo->harderror;
 	}
 

include/linux/nbd.h

@@ -68,6 +68,7 @@ struct nbd_device {
 	u64 bytesize;
 	pid_t pid; /* pid of nbd-client, if attached */
 	int xmit_timeout;
+	int disconnect; /* a disconnect has been requested by user */
 };
 
 #endif