/*
 * Network block device - make block devices work over TCP
 *
 * Note that you can not swap over this thing, yet. Seems to work but
 * deadlocks sometimes - you can not swap over TCP in general.
 * 
 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
 *
 * This file is released under GPLv2 or later.
 *
 * (part of code stolen from loop.c)
 */

#include <linux/major.h>

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/bio.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/ioctl.h>
#include <linux/mutex.h>
#include <linux/compiler.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <net/sock.h>
#include <linux/net.h>
#include <linux/kthread.h>

#include <asm/uaccess.h>
#include <asm/types.h>

#include <linux/nbd.h>

#define NBD_MAGIC 0x68797548

#ifdef NDEBUG
#define dprintk(flags, fmt...)
#else /* NDEBUG */
#define dprintk(flags, fmt...) do { \
        if (debugflags & (flags)) printk(KERN_DEBUG fmt); \
} while (0)
#define DBG_IOCTL       0x0004
#define DBG_INIT        0x0010
#define DBG_EXIT        0x0020
#define DBG_BLKDEV      0x0100
#define DBG_RX          0x0200
#define DBG_TX          0x0400
static unsigned int debugflags;
#endif /* NDEBUG */

static unsigned int nbds_max = 16;
static struct nbd_device *nbd_dev;
static int max_part;

/*
 * 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 DEFINE_SPINLOCK(nbd_lock);

#ifndef NDEBUG
static const char *ioctl_cmd_to_ascii(int cmd)
{
        switch (cmd) {
        case NBD_SET_SOCK: return "set-sock";
        case NBD_SET_BLKSIZE: return "set-blksize";
        case NBD_SET_SIZE: return "set-size";
        case NBD_SET_TIMEOUT: return "set-timeout";
        case NBD_SET_FLAGS: return "set-flags";
        case NBD_DO_IT: return "do-it";
        case NBD_CLEAR_SOCK: return "clear-sock";
        case NBD_CLEAR_QUE: return "clear-que";
        case NBD_PRINT_DEBUG: return "print-debug";
        case NBD_SET_SIZE_BLOCKS: return "set-size-blocks";
        case NBD_DISCONNECT: return "disconnect";
        case BLKROSET: return "set-read-only";
        case BLKFLSBUF: return "flush-buffer-cache";
        }
        return "unknown";
}

static const char *nbdcmd_to_ascii(int cmd)
{
        switch (cmd) {
        case  NBD_CMD_READ: return "read";
        case NBD_CMD_WRITE: return "write";
        case  NBD_CMD_DISC: return "disconnect";
        case  NBD_CMD_TRIM: return "trim/discard";
        }
        return "invalid";
}
#endif /* NDEBUG */

static void nbd_end_request(struct request *req)
{
        int error = req->errors ? -EIO : 0;
        struct request_queue *q = req->q;
        unsigned long flags;

        dprintk(DBG_BLKDEV, "%s: request %p: %s\n", req->rq_disk->disk_name,
                        req, error ? "failed" : "done");

        spin_lock_irqsave(q->queue_lock, flags);
        __blk_end_request_all(req, error);
        spin_unlock_irqrestore(q->queue_lock, flags);
}

static void sock_shutdown(struct nbd_device *nbd, int lock)
{
        /* Forcibly shutdown the socket causing all listeners
         * to error
         *
         * FIXME: This code is duplicated from sys_shutdown, but
         * there should be a more generic interface rather than
         * calling socket ops directly here */
        if (lock)
                mutex_lock(&nbd->tx_lock);
        if (nbd->sock) {
                dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
                kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
                nbd->sock = NULL;
        }
        if (lock)
                mutex_unlock(&nbd->tx_lock);
}

static void nbd_xmit_timeout(unsigned long arg)
{
        struct task_struct *task = (struct task_struct *)arg;

        printk(KERN_WARNING "nbd: killing hung xmit (%s, pid: %d)\n",
                task->comm, task->pid);
        force_sig(SIGKILL, task);
}

/*
 *  Send or receive packet.
 */
static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
                int msg_flags)
{
        struct socket *sock = nbd->sock;
        int result;
        struct msghdr msg;
        struct kvec iov;
        sigset_t blocked, oldset;
        unsigned long pflags = current->flags;

        if (unlikely(!sock)) {
                dev_err(disk_to_dev(nbd->disk),
                        "Attempted %s on closed socket in sock_xmit\n",
                        (send ? "send" : "recv"));
                return -EINVAL;
        }

        /* Allow interception of SIGKILL only
         * Don't allow other signals to interrupt the transmission */
        siginitsetinv(&blocked, sigmask(SIGKILL));
        sigprocmask(SIG_SETMASK, &blocked, &oldset);

        current->flags |= PF_MEMALLOC;
        do {
                sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
                iov.iov_base = buf;
                iov.iov_len = size;
                msg.msg_name = NULL;
                msg.msg_namelen = 0;
                msg.msg_control = NULL;
                msg.msg_controllen = 0;
                msg.msg_flags = msg_flags | MSG_NOSIGNAL;

                if (send) {
                        struct timer_list ti;

                        if (nbd->xmit_timeout) {
                                init_timer(&ti);
                                ti.function = nbd_xmit_timeout;
                                ti.data = (unsigned long)current;
                                ti.expires = jiffies + nbd->xmit_timeout;
                                add_timer(&ti);
                        }
                        result = kernel_sendmsg(sock, &msg, &iov, 1, size);
                        if (nbd->xmit_timeout)
                                del_timer_sync(&ti);
                } else
                        result = kernel_recvmsg(sock, &msg, &iov, 1, size,
                                                msg.msg_flags);

                if (signal_pending(current)) {
                        siginfo_t info;
                        printk(KERN_WARNING "nbd (pid %d: %s) got signal %d\n",
                                task_pid_nr(current), current->comm,
                                dequeue_signal_lock(current, &current->blocked, &info));
                        result = -EINTR;
                        sock_shutdown(nbd, !send);
                        break;
                }

                if (result <= 0) {
                        if (result == 0)
                                result = -EPIPE; /* short read */
                        break;
                }
                size -= result;
                buf += result;
        } while (size > 0);

        sigprocmask(SIG_SETMASK, &oldset, NULL);
        tsk_restore_flags(current, pflags, PF_MEMALLOC);

        return result;
}

static inline int sock_send_bvec(struct nbd_device *nbd, struct bio_vec *bvec,
                int flags)
{
        int result;
        void *kaddr = kmap(bvec->bv_page);
        result = sock_xmit(nbd, 1, kaddr + bvec->bv_offset,
                           bvec->bv_len, flags);
        kunmap(bvec->bv_page);
        return result;
}

/* always call with the tx_lock held */
static int nbd_send_req(struct nbd_device *nbd, struct request *req)
{
        int result, flags;
        struct nbd_request request;
        unsigned long size = blk_rq_bytes(req);

        request.magic = htonl(NBD_REQUEST_MAGIC);
        request.type = htonl(nbd_cmd(req));
        request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
        request.len = htonl(size);
        memcpy(request.handle, &req, sizeof(req));

        dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%uB)\n",
                        nbd->disk->disk_name, req,
                        nbdcmd_to_ascii(nbd_cmd(req)),
                        (unsigned long long)blk_rq_pos(req) << 9,
                        blk_rq_bytes(req));
        result = sock_xmit(nbd, 1, &request, sizeof(request),
                        (nbd_cmd(req) == NBD_CMD_WRITE) ? MSG_MORE : 0);
        if (result <= 0) {
                dev_err(disk_to_dev(nbd->disk),
                        "Send control failed (result %d)\n", result);
                goto error_out;
        }

        if (nbd_cmd(req) == NBD_CMD_WRITE) {
                struct req_iterator iter;
                struct bio_vec *bvec;
                /*
                 * we are really probing at internals to determine
                 * whether to set MSG_MORE or not...
                 */
                rq_for_each_segment(bvec, req, iter) {
                        flags = 0;
                        if (!rq_iter_last(req, iter))
                                flags = MSG_MORE;
                        dprintk(DBG_TX, "%s: request %p: sending %d bytes data\n",
                                        nbd->disk->disk_name, req, bvec->bv_len);
                        result = sock_send_bvec(nbd, bvec, flags);
                        if (result <= 0) {
                                dev_err(disk_to_dev(nbd->disk),
                                        "Send data failed (result %d)\n",
                                        result);
                                goto error_out;
                        }
                }
        }
        return 0;

error_out:
        return -EIO;
}

static struct request *nbd_find_request(struct nbd_device *nbd,
                                        struct request *xreq)
{
        struct request *req, *tmp;
        int err;

        err = wait_event_interruptible(nbd->active_wq, nbd->active_req != xreq);
        if (unlikely(err))
                goto out;

        spin_lock(&nbd->queue_lock);
        list_for_each_entry_safe(req, tmp, &nbd->queue_head, queuelist) {
                if (req != xreq)
                        continue;
                list_del_init(&req->queuelist);
                spin_unlock(&nbd->queue_lock);
                return req;
        }
        spin_unlock(&nbd->queue_lock);

        err = -ENOENT;

out:
        return ERR_PTR(err);
}

static inline int sock_recv_bvec(struct nbd_device *nbd, struct bio_vec *bvec)
{
        int result;
        void *kaddr = kmap(bvec->bv_page);
        result = sock_xmit(nbd, 0, kaddr + bvec->bv_offset, bvec->bv_len,
                        MSG_WAITALL);
        kunmap(bvec->bv_page);
        return result;
}

/* NULL returned = something went wrong, inform userspace */
static struct request *nbd_read_stat(struct nbd_device *nbd)
{
        int result;
        struct nbd_reply reply;
        struct request *req;

        reply.magic = 0;
        result = sock_xmit(nbd, 0, &reply, sizeof(reply), MSG_WAITALL);
        if (result <= 0) {
                dev_err(disk_to_dev(nbd->disk),
                        "Receive control failed (result %d)\n", result);
                goto harderror;
        }

        if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
                dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
                                (unsigned long)ntohl(reply.magic));
                result = -EPROTO;
                goto harderror;
        }

        req = nbd_find_request(nbd, *(struct request **)reply.handle);
        if (IS_ERR(req)) {
                result = PTR_ERR(req);
                if (result != -ENOENT)
                        goto harderror;

                dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%p)\n",
                        reply.handle);
                result = -EBADR;
                goto harderror;
        }

        if (ntohl(reply.error)) {
                dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
                        ntohl(reply.error));
                req->errors++;
                return req;
        }

        dprintk(DBG_RX, "%s: request %p: got reply\n",
                        nbd->disk->disk_name, req);
        if (nbd_cmd(req) == NBD_CMD_READ) {
                struct req_iterator iter;
                struct bio_vec *bvec;

                rq_for_each_segment(bvec, req, iter) {
                        result = sock_recv_bvec(nbd, bvec);
                        if (result <= 0) {
                                dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
                                        result);
                                req->errors++;
                                return req;
                        }
                        dprintk(DBG_RX, "%s: request %p: got %d bytes data\n",
                                nbd->disk->disk_name, req, bvec->bv_len);
                }
        }
        return req;
harderror:
        nbd->harderror = result;
        return NULL;
}

static ssize_t pid_show(struct device *dev,
                        struct device_attribute *attr, char *buf)
{
        struct gendisk *disk = dev_to_disk(dev);

        return sprintf(buf, "%ld\n",
                (long) ((struct nbd_device *)disk->private_data)->pid);
}

static struct device_attribute pid_attr = {
        .attr = { .name = "pid", .mode = S_IRUGO},
        .show = pid_show,
};

static int nbd_do_it(struct nbd_device *nbd)
{
        struct request *req;
        int ret;

        BUG_ON(nbd->magic != NBD_MAGIC);

        sk_set_memalloc(nbd->sock->sk);
        nbd->pid = task_pid_nr(current);
        ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
        if (ret) {
                dev_err(disk_to_dev(nbd->disk), "device_create_file failed!\n");
                nbd->pid = 0;
                return ret;
        }

        while ((req = nbd_read_stat(nbd)) != NULL)
                nbd_end_request(req);

        device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
        nbd->pid = 0;
        return 0;
}

static void nbd_clear_que(struct nbd_device *nbd)
{
        struct request *req;

        BUG_ON(nbd->magic != NBD_MAGIC);

        /*
         * Because we have set nbd->sock to NULL under the tx_lock, all
         * modifications to the list must have completed by now.  For
         * the same reason, the active_req must be NULL.
         *
         * As a consequence, we don't need to take the spin lock while
         * purging the list here.
         */
        BUG_ON(nbd->sock);
        BUG_ON(nbd->active_req);

        while (!list_empty(&nbd->queue_head)) {
                req = list_entry(nbd->queue_head.next, struct request,
                                 queuelist);
                list_del_init(&req->queuelist);
                req->errors++;
                nbd_end_request(req);
        }

        while (!list_empty(&nbd->waiting_queue)) {
                req = list_entry(nbd->waiting_queue.next, struct request,
                                 queuelist);
                list_del_init(&req->queuelist);
                req->errors++;
                nbd_end_request(req);
        }
}


static void nbd_handle_req(struct nbd_device *nbd, struct request *req)
{
        if (req->cmd_type != REQ_TYPE_FS)
                goto error_out;

        nbd_cmd(req) = NBD_CMD_READ;
        if (rq_data_dir(req) == WRITE) {
                if ((req->cmd_flags & REQ_DISCARD)) {
                        WARN_ON(!(nbd->flags & NBD_FLAG_SEND_TRIM));
                        nbd_cmd(req) = NBD_CMD_TRIM;
                } else
                        nbd_cmd(req) = NBD_CMD_WRITE;
                if (nbd->flags & NBD_FLAG_READ_ONLY) {
                        dev_err(disk_to_dev(nbd->disk),
                                "Write on read-only\n");
                        goto error_out;
                }
        }

        req->errors = 0;

        mutex_lock(&nbd->tx_lock);
        if (unlikely(!nbd->sock)) {
                mutex_unlock(&nbd->tx_lock);
                dev_err(disk_to_dev(nbd->disk),
                        "Attempted send on closed socket\n");
                goto error_out;
        }

        nbd->active_req = req;

        if (nbd_send_req(nbd, req) != 0) {
                dev_err(disk_to_dev(nbd->disk), "Request send failed\n");
                req->errors++;
                nbd_end_request(req);
        } else {
                spin_lock(&nbd->queue_lock);
                list_add_tail(&req->queuelist, &nbd->queue_head);
                spin_unlock(&nbd->queue_lock);
        }

        nbd->active_req = NULL;
        mutex_unlock(&nbd->tx_lock);
        wake_up_all(&nbd->active_wq);

        return;

error_out:
        req->errors++;
        nbd_end_request(req);
}

static int nbd_thread(void *data)
{
        struct nbd_device *nbd = data;
        struct request *req;

        set_user_nice(current, -20);
        while (!kthread_should_stop() || !list_empty(&nbd->waiting_queue)) {
                /* wait for something to do */
                wait_event_interruptible(nbd->waiting_wq,
                                         kthread_should_stop() ||
                                         !list_empty(&nbd->waiting_queue));

                /* extract request */
                if (list_empty(&nbd->waiting_queue))
                        continue;

                spin_lock_irq(&nbd->queue_lock);
                req = list_entry(nbd->waiting_queue.next, struct request,
                                 queuelist);
                list_del_init(&req->queuelist);
                spin_unlock_irq(&nbd->queue_lock);

                /* handle request */
                nbd_handle_req(nbd, req);
        }
        return 0;
}

/*
 * We always wait for result of write, for now. It would be nice to make it optional
 * in future
 * if ((rq_data_dir(req) == WRITE) && (nbd->flags & NBD_WRITE_NOCHK))
 *   { printk( "Warning: Ignoring result!\n"); nbd_end_request( req ); }
 */

static void do_nbd_request(struct request_queue *q)
{
        struct request *req;
        
        while ((req = blk_fetch_request(q)) != NULL) {
                struct nbd_device *nbd;

                spin_unlock_irq(q->queue_lock);

                dprintk(DBG_BLKDEV, "%s: request %p: dequeued (flags=%x)\n",
                                req->rq_disk->disk_name, req, req->cmd_type);

                nbd = req->rq_disk->private_data;

                BUG_ON(nbd->magic != NBD_MAGIC);

                if (unlikely(!nbd->sock)) {
                        dev_err(disk_to_dev(nbd->disk),
                                "Attempted send on closed socket\n");
                        req->errors++;
                        nbd_end_request(req);
                        spin_lock_irq(q->queue_lock);
                        continue;
                }

                spin_lock_irq(&nbd->queue_lock);
                list_add_tail(&req->queuelist, &nbd->waiting_queue);
                spin_unlock_irq(&nbd->queue_lock);

                wake_up(&nbd->waiting_wq);

                spin_lock_irq(q->queue_lock);
        }
}

/* Must be called with tx_lock held */

static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
                       unsigned int cmd, unsigned long arg)
{
        switch (cmd) {
        case NBD_DISCONNECT: {
                struct request sreq;

                dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");

                blk_rq_init(NULL, &sreq);
                sreq.cmd_type = REQ_TYPE_SPECIAL;
                nbd_cmd(&sreq) = NBD_CMD_DISC;
                if (!nbd->sock)
                        return -EINVAL;
                nbd_send_req(nbd, &sreq);
                return 0;
        }
 
        case NBD_CLEAR_SOCK: {
                struct file *file;

                nbd->sock = NULL;
                file = nbd->file;
                nbd->file = NULL;
                nbd_clear_que(nbd);
                BUG_ON(!list_empty(&nbd->queue_head));
                BUG_ON(!list_empty(&nbd->waiting_queue));
                if (file)
                        fput(file);
                return 0;
        }

        case NBD_SET_SOCK: {
                struct file *file;
                if (nbd->file)
                        return -EBUSY;
                file = fget(arg);
                if (file) {
                        struct inode *inode = file->f_path.dentry->d_inode;
                        if (S_ISSOCK(inode->i_mode)) {
                                nbd->file = file;
                                nbd->sock = SOCKET_I(inode);
                                if (max_part > 0)
                                        bdev->bd_invalidated = 1;
                                return 0;
                        } else {
                                fput(file);
                        }
                }
                return -EINVAL;
        }

        case NBD_SET_BLKSIZE:
                nbd->blksize = arg;
                nbd->bytesize &= ~(nbd->blksize-1);
                bdev->bd_inode->i_size = nbd->bytesize;
                set_blocksize(bdev, nbd->blksize);
                set_capacity(nbd->disk, nbd->bytesize >> 9);
                return 0;

        case NBD_SET_SIZE:
                nbd->bytesize = arg & ~(nbd->blksize-1);
                bdev->bd_inode->i_size = nbd->bytesize;
                set_blocksize(bdev, nbd->blksize);
                set_capacity(nbd->disk, nbd->bytesize >> 9);
                return 0;

        case NBD_SET_TIMEOUT:
                nbd->xmit_timeout = arg * HZ;
                return 0;

        case NBD_SET_FLAGS:
                nbd->flags = arg;
                return 0;

        case NBD_SET_SIZE_BLOCKS:
                nbd->bytesize = ((u64) arg) * nbd->blksize;
                bdev->bd_inode->i_size = nbd->bytesize;
                set_blocksize(bdev, nbd->blksize);
                set_capacity(nbd->disk, nbd->bytesize >> 9);
                return 0;

        case NBD_DO_IT: {
                struct task_struct *thread;
                struct file *file;
                int error;

                if (nbd->pid)
                        return -EBUSY;
                if (!nbd->file)
                        return -EINVAL;

                mutex_unlock(&nbd->tx_lock);

                if (nbd->flags & NBD_FLAG_SEND_TRIM)
                        queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
                                nbd->disk->queue);

                thread = kthread_create(nbd_thread, nbd, nbd->disk->disk_name);
                if (IS_ERR(thread)) {
                        mutex_lock(&nbd->tx_lock);
                        return PTR_ERR(thread);
                }
                wake_up_process(thread);
                error = nbd_do_it(nbd);
                kthread_stop(thread);

                mutex_lock(&nbd->tx_lock);
                if (error)
                        return error;
                sock_shutdown(nbd, 0);
                file = nbd->file;
                nbd->file = NULL;
                nbd_clear_que(nbd);
                dev_warn(disk_to_dev(nbd->disk), "queue cleared\n");
                queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
                if (file)
                        fput(file);
                nbd->bytesize = 0;
                bdev->bd_inode->i_size = 0;
                set_capacity(nbd->disk, 0);
                if (max_part > 0)
                        ioctl_by_bdev(bdev, BLKRRPART, 0);
                return nbd->harderror;
        }

        case NBD_CLEAR_QUE:
                /*
                 * This is for compatibility only.  The queue is always cleared
                 * by NBD_DO_IT or NBD_CLEAR_SOCK.
                 */
                BUG_ON(!nbd->sock && !list_empty(&nbd->queue_head));
                return 0;

        case NBD_PRINT_DEBUG:
                dev_info(disk_to_dev(nbd->disk),
                        "next = %p, prev = %p, head = %p\n",
                        nbd->queue_head.next, nbd->queue_head.prev,
                        &nbd->queue_head);
                return 0;
        }
        return -ENOTTY;
}

static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
                     unsigned int cmd, unsigned long arg)
{
        struct nbd_device *nbd = bdev->bd_disk->private_data;
        int error;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        BUG_ON(nbd->magic != NBD_MAGIC);

        /* Anyone capable of this syscall can do *real bad* things */
        dprintk(DBG_IOCTL, "%s: nbd_ioctl cmd=%s(0x%x) arg=%lu\n",
                nbd->disk->disk_name, ioctl_cmd_to_ascii(cmd), cmd, arg);

        mutex_lock(&nbd->tx_lock);
        error = __nbd_ioctl(bdev, nbd, cmd, arg);
        mutex_unlock(&nbd->tx_lock);

        return error;
}

static const struct block_device_operations nbd_fops =
{
        .owner =        THIS_MODULE,
        .ioctl =        nbd_ioctl,
};

/*
 * And here should be modules and kernel interface 
 *  (Just smiley confuses emacs :-)
 */

static int __init nbd_init(void)
{
        int err = -ENOMEM;
        int i;
        int part_shift;

        BUILD_BUG_ON(sizeof(struct nbd_request) != 28);

        if (max_part < 0) {
                printk(KERN_ERR "nbd: max_part must be >= 0\n");
                return -EINVAL;
        }

        nbd_dev = kcalloc(nbds_max, sizeof(*nbd_dev), GFP_KERNEL);
        if (!nbd_dev)
                return -ENOMEM;

        part_shift = 0;
        if (max_part > 0) {
                part_shift = fls(max_part);

                /*
                 * Adjust max_part according to part_shift as it is exported
                 * to user space so that user can know the max number of
                 * partition kernel should be able to manage.
                 *
                 * Note that -1 is required because partition 0 is reserved
                 * for the whole disk.
                 */
                max_part = (1UL << part_shift) - 1;
        }

        if ((1UL << part_shift) > DISK_MAX_PARTS)
                return -EINVAL;

        if (nbds_max > 1UL << (MINORBITS - part_shift))
                return -EINVAL;

        for (i = 0; i < nbds_max; i++) {
                struct gendisk *disk = alloc_disk(1 << part_shift);
                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 = blk_init_queue(do_nbd_request, &nbd_lock);
                if (!disk->queue) {
                        put_disk(disk);
                        goto out;
                }
                /*
                 * Tell the block layer that we are not a rotational device
                 */
                queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);
                disk->queue->limits.discard_granularity = 512;
                disk->queue->limits.max_discard_sectors = UINT_MAX;
                disk->queue->limits.discard_zeroes_data = 0;
        }

        if (register_blkdev(NBD_MAJOR, "nbd")) {
                err = -EIO;
                goto out;
        }

        printk(KERN_INFO "nbd: registered device at major %d\n", NBD_MAJOR);
        dprintk(DBG_INIT, "nbd: debugflags=0x%x\n", debugflags);

        for (i = 0; i < nbds_max; i++) {
                struct gendisk *disk = nbd_dev[i].disk;
                nbd_dev[i].file = NULL;
                nbd_dev[i].magic = NBD_MAGIC;
                nbd_dev[i].flags = 0;
                INIT_LIST_HEAD(&nbd_dev[i].waiting_queue);
                spin_lock_init(&nbd_dev[i].queue_lock);
                INIT_LIST_HEAD(&nbd_dev[i].queue_head);
                mutex_init(&nbd_dev[i].tx_lock);
                init_waitqueue_head(&nbd_dev[i].active_wq);
                init_waitqueue_head(&nbd_dev[i].waiting_wq);
                nbd_dev[i].blksize = 1024;
                nbd_dev[i].bytesize = 0;
                disk->major = NBD_MAJOR;
                disk->first_minor = i << part_shift;
                disk->fops = &nbd_fops;
                disk->private_data = &nbd_dev[i];
                sprintf(disk->disk_name, "nbd%d", i);
                set_capacity(disk, 0);
                add_disk(disk);
        }

        return 0;
out:
        while (i--) {
                blk_cleanup_queue(nbd_dev[i].disk->queue);
                put_disk(nbd_dev[i].disk);
        }
        kfree(nbd_dev);
        return err;
}

static void __exit nbd_cleanup(void)
{
        int 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);
                        put_disk(disk);
                }
        }
        unregister_blkdev(NBD_MAJOR, "nbd");
        kfree(nbd_dev);
        printk(KERN_INFO "nbd: unregistered device at major %d\n", NBD_MAJOR);
}

module_init(nbd_init);
module_exit(nbd_cleanup);

MODULE_DESCRIPTION("Network Block Device");
MODULE_LICENSE("GPL");

module_param(nbds_max, int, 0444);
MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
module_param(max_part, int, 0444);
MODULE_PARM_DESC(max_part, "number of partitions per device (default: 0)");
#ifndef NDEBUG
module_param(debugflags, int, 0644);
MODULE_PARM_DESC(debugflags, "flags for controlling debug output");
#endif