nbd.c

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/*
 * 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 <[email protected]>
 * Parts copyright 2001 Steven Whitehouse <[email protected]>
 *
 * 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