Re: [Nbd] [PATCH] nbd: correct disconnect behavior

On Wed, 19 Jun 2013 17:09:18 -0400 (EDT) Paul Clements <paul.clements@...124...> wrote:

This sounds like something which users of 3.10 and earlier kernels
might want, so I added the Cc:stable tag. Please let me know if
you disagree.

That is a good idea. It would be useful in stable.

> --- 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;
> }

hm, how does nbd work... Hard to tell as nothing seems to be documented
anywhere :(

I think most people look at the nbd-client to see. :)

But I will work on some docs for the ioctls...

Briefly, though, it goes something like this:

nbd-client and nbd-server negotiate parameters, including the server telling the client how big the export is

Then the nbd-client does a series of ioctls to set up the device:

NBD_SET_SIZE - set the size of the device

NBD_SET_SOCK - tell the kernel which socket to use

NBD_DO_IT - this ioctl lasts for the life of the device and causes nbd-client to go into a receive loop, handling I/O replies from the nbd-server

NBD_DISCONNECT, meanwhile, can be called from a separate thread (usually "nbd-client -d" calls it). This requests a disconnect of the device.

> --- 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 */
> };

The cool kids are using bool lately ;)

Hey, maybe I want to be able to compile with gcc 2.7.2 ? :)