[PATCH] nbd: correct disconnect behavior

[Paul Clements <paul.clements@steeleye.com>]

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>
---

 drivers/block/nbd.c |    5 +++++
 include/linux/nbd.h |    1 +
 2 files changed, 6 insertions(+)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 7fecc78..8b7664d 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -623,6 +623,8 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		if (!nbd->sock)
 			return -EINVAL;
 
+		nbd->disconnect = 1;
+
 		nbd_send_req(nbd, &sreq);
                 return 0;
 	}
@@ -654,6 +656,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 				nbd->sock = SOCKET_I(inode);
 				if (max_part > 0)
 					bdev->bd_invalidated = 1;
+				nbd->disconnect = 0; /* we're connected now */
 				return 0;
 			} else {
 				fput(file);
@@ -742,6 +745,8 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
 		set_capacity(nbd->disk, 0);
 		if (max_part > 0)
 			ioctl_by_bdev(bdev, BLKRRPART, 0);
+		if (nbd->disconnect) /* user requested, ignore socket errors */
+			return 0;
 		return nbd->harderror;
 	}
 
diff --git a/include/linux/nbd.h b/include/linux/nbd.h
index 4871170..ae4981e 100644
--- a/include/linux/nbd.h
+++ b/include/linux/nbd.h
@@ -41,6 +41,7 @@ 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