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nbd.c

/*
 * 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 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/compiler.h>
#include <linux/err.h>
#include <linux/kernel.h>
#include <net/sock.h>
#include <linux/net.h>

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

#include <linux/nbd.h>

#define LO_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[MAX_NBD];

/*
 * 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_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";
      }
      return "invalid";
}
#endif /* NDEBUG */

static void nbd_end_request(struct request *req)
{
      int uptodate = (req->errors == 0) ? 1 : 0;
      struct request_queue *q = req->q;
      unsigned long flags;

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

      spin_lock_irqsave(q->queue_lock, flags);
      if (!end_that_request_first(req, uptodate, req->nr_sectors)) {
            end_that_request_last(req, uptodate);
      }
      spin_unlock_irqrestore(q->queue_lock, flags);
}

static void sock_shutdown(struct nbd_device *lo, 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(&lo->tx_lock);
      if (lo->sock) {
            printk(KERN_WARNING "%s: shutting down socket\n",
                  lo->disk->disk_name);
            kernel_sock_shutdown(lo->sock, SHUT_RDWR);
            lo->sock = NULL;
      }
      if (lock)
            mutex_unlock(&lo->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 *lo, int send, void *buf, int size,
            int msg_flags)
{
      struct socket *sock = lo->sock;
      int result;
      struct msghdr msg;
      struct kvec iov;
      sigset_t blocked, oldset;

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

      do {
            sock->sk->sk_allocation = GFP_NOIO;
            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 (lo->xmit_timeout) {
                        init_timer(&ti);
                        ti.function = nbd_xmit_timeout;
                        ti.data = (unsigned long)current;
                        ti.expires = jiffies + lo->xmit_timeout;
                        add_timer(&ti);
                  }
                  result = kernel_sendmsg(sock, &msg, &iov, 1, size);
                  if (lo->xmit_timeout)
                        del_timer_sync(&ti);
            } else
                  result = kernel_recvmsg(sock, &msg, &iov, 1, size, 0);

            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(lo, !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);

      return result;
}

static inline int sock_send_bvec(struct nbd_device *lo, struct bio_vec *bvec,
            int flags)
{
      int result;
      void *kaddr = kmap(bvec->bv_page);
      result = sock_xmit(lo, 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 *lo, struct request *req)
{
      int result, flags;
      struct nbd_request request;
      unsigned long size = req->nr_sectors << 9;

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

      dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%luB)\n",
                  lo->disk->disk_name, req,
                  nbdcmd_to_ascii(nbd_cmd(req)),
                  (unsigned long long)req->sector << 9,
                  req->nr_sectors << 9);
      result = sock_xmit(lo, 1, &request, sizeof(request),
                  (nbd_cmd(req) == NBD_CMD_WRITE) ? MSG_MORE : 0);
      if (result <= 0) {
            printk(KERN_ERR "%s: Send control failed (result %d)\n",
                        lo->disk->disk_name, 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",
                              lo->disk->disk_name, req, bvec->bv_len);
                  result = sock_send_bvec(lo, bvec, flags);
                  if (result <= 0) {
                        printk(KERN_ERR "%s: Send data failed (result %d)\n",
                                    lo->disk->disk_name, result);
                        goto error_out;
                  }
            }
      }
      return 0;

error_out:
      return 1;
}

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

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

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

      err = -ENOENT;

out:
      return ERR_PTR(err);
}

static inline int sock_recv_bvec(struct nbd_device *lo, struct bio_vec *bvec)
{
      int result;
      void *kaddr = kmap(bvec->bv_page);
      result = sock_xmit(lo, 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 *lo)
{
      int result;
      struct nbd_reply reply;
      struct request *req;

      reply.magic = 0;
      result = sock_xmit(lo, 0, &reply, sizeof(reply), MSG_WAITALL);
      if (result <= 0) {
            printk(KERN_ERR "%s: Receive control failed (result %d)\n",
                        lo->disk->disk_name, result);
            goto harderror;
      }

      if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
            printk(KERN_ERR "%s: Wrong magic (0x%lx)\n",
                        lo->disk->disk_name,
                        (unsigned long)ntohl(reply.magic));
            result = -EPROTO;
            goto harderror;
      }

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

            printk(KERN_ERR "%s: Unexpected reply (%p)\n",
                        lo->disk->disk_name, reply.handle);
            result = -EBADR;
            goto harderror;
      }

      if (ntohl(reply.error)) {
            printk(KERN_ERR "%s: Other side returned error (%d)\n",
                        lo->disk->disk_name, ntohl(reply.error));
            req->errors++;
            return req;
      }

      dprintk(DBG_RX, "%s: request %p: got reply\n",
                  lo->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(lo, bvec);
                  if (result <= 0) {
                        printk(KERN_ERR "%s: Receive data failed (result %d)\n",
                                    lo->disk->disk_name, result);
                        req->errors++;
                        return req;
                  }
                  dprintk(DBG_RX, "%s: request %p: got %d bytes data\n",
                        lo->disk->disk_name, req, bvec->bv_len);
            }
      }
      return req;
harderror:
      lo->harderror = result;
      return NULL;
}

static ssize_t pid_show(struct gendisk *disk, char *page)
{
      return sprintf(page, "%ld\n",
            (long) ((struct nbd_device *)disk->private_data)->pid);
}

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

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

      BUG_ON(lo->magic != LO_MAGIC);

      lo->pid = current->pid;
      ret = sysfs_create_file(&lo->disk->kobj, &pid_attr.attr);
      if (ret) {
            printk(KERN_ERR "nbd: sysfs_create_file failed!");
            return ret;
      }

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

      sysfs_remove_file(&lo->disk->kobj, &pid_attr.attr);
      return 0;
}

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

      BUG_ON(lo->magic != LO_MAGIC);

      /*
       * Because we have set lo->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(lo->sock);
      BUG_ON(lo->active_req);

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


/*
 * 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) && (lo->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 = elv_next_request(q)) != NULL) {
            struct nbd_device *lo;

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

            if (!blk_fs_request(req))
                  goto error_out;

            lo = req->rq_disk->private_data;

            BUG_ON(lo->magic != LO_MAGIC);

            nbd_cmd(req) = NBD_CMD_READ;
            if (rq_data_dir(req) == WRITE) {
                  nbd_cmd(req) = NBD_CMD_WRITE;
                  if (lo->flags & NBD_READ_ONLY) {
                        printk(KERN_ERR "%s: Write on read-only\n",
                                    lo->disk->disk_name);
                        goto error_out;
                  }
            }

            req->errors = 0;
            spin_unlock_irq(q->queue_lock);

            mutex_lock(&lo->tx_lock);
            if (unlikely(!lo->sock)) {
                  mutex_unlock(&lo->tx_lock);
                  printk(KERN_ERR "%s: Attempted send on closed socket\n",
                         lo->disk->disk_name);
                  req->errors++;
                  nbd_end_request(req);
                  spin_lock_irq(q->queue_lock);
                  continue;
            }

            lo->active_req = req;

            if (nbd_send_req(lo, req) != 0) {
                  printk(KERN_ERR "%s: Request send failed\n",
                              lo->disk->disk_name);
                  req->errors++;
                  nbd_end_request(req);
            } else {
                  spin_lock(&lo->queue_lock);
                  list_add(&req->queuelist, &lo->queue_head);
                  spin_unlock(&lo->queue_lock);
            }

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

            spin_lock_irq(q->queue_lock);
            continue;

error_out:
            req->errors++;
            spin_unlock(q->queue_lock);
            nbd_end_request(req);
            spin_lock(q->queue_lock);
      }
}

static int nbd_ioctl(struct inode *inode, struct file *file,
                 unsigned int cmd, unsigned long arg)
{
      struct nbd_device *lo = inode->i_bdev->bd_disk->private_data;
      int error;
      struct request sreq ;

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

      BUG_ON(lo->magic != LO_MAGIC);

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

      switch (cmd) {
      case NBD_DISCONNECT:
              printk(KERN_INFO "%s: NBD_DISCONNECT\n", lo->disk->disk_name);
            sreq.cmd_type = REQ_TYPE_SPECIAL;
            nbd_cmd(&sreq) = NBD_CMD_DISC;
            /*
             * Set these to sane values in case server implementation
             * fails to check the request type first and also to keep
             * debugging output cleaner.
             */
            sreq.sector = 0;
            sreq.nr_sectors = 0;
                if (!lo->sock)
                  return -EINVAL;
            mutex_lock(&lo->tx_lock);
                nbd_send_req(lo, &sreq);
            mutex_unlock(&lo->tx_lock);
                return 0;
 
      case NBD_CLEAR_SOCK:
            error = 0;
            mutex_lock(&lo->tx_lock);
            lo->sock = NULL;
            mutex_unlock(&lo->tx_lock);
            file = lo->file;
            lo->file = NULL;
            nbd_clear_que(lo);
            BUG_ON(!list_empty(&lo->queue_head));
            if (file)
                  fput(file);
            return error;
      case NBD_SET_SOCK:
            if (lo->file)
                  return -EBUSY;
            error = -EINVAL;
            file = fget(arg);
            if (file) {
                  inode = file->f_path.dentry->d_inode;
                  if (S_ISSOCK(inode->i_mode)) {
                        lo->file = file;
                        lo->sock = SOCKET_I(inode);
                        error = 0;
                  } else {
                        fput(file);
                  }
            }
            return error;
      case NBD_SET_BLKSIZE:
            lo->blksize = arg;
            lo->bytesize &= ~(lo->blksize-1);
            inode->i_bdev->bd_inode->i_size = lo->bytesize;
            set_blocksize(inode->i_bdev, lo->blksize);
            set_capacity(lo->disk, lo->bytesize >> 9);
            return 0;
      case NBD_SET_SIZE:
            lo->bytesize = arg & ~(lo->blksize-1);
            inode->i_bdev->bd_inode->i_size = lo->bytesize;
            set_blocksize(inode->i_bdev, lo->blksize);
            set_capacity(lo->disk, lo->bytesize >> 9);
            return 0;
      case NBD_SET_TIMEOUT:
            lo->xmit_timeout = arg * HZ;
            return 0;
      case NBD_SET_SIZE_BLOCKS:
            lo->bytesize = ((u64) arg) * lo->blksize;
            inode->i_bdev->bd_inode->i_size = lo->bytesize;
            set_blocksize(inode->i_bdev, lo->blksize);
            set_capacity(lo->disk, lo->bytesize >> 9);
            return 0;
      case NBD_DO_IT:
            if (!lo->file)
                  return -EINVAL;
            error = nbd_do_it(lo);
            if (error)
                  return error;
            sock_shutdown(lo, 1);
            file = lo->file;
            lo->file = NULL;
            nbd_clear_que(lo);
            printk(KERN_WARNING "%s: queue cleared\n", lo->disk->disk_name);
            if (file)
                  fput(file);
            lo->bytesize = 0;
            inode->i_bdev->bd_inode->i_size = 0;
            set_capacity(lo->disk, 0);
            return lo->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(!lo->sock && !list_empty(&lo->queue_head));
            return 0;
      case NBD_PRINT_DEBUG:
            printk(KERN_INFO "%s: next = %p, prev = %p, head = %p\n",
                  inode->i_bdev->bd_disk->disk_name,
                  lo->queue_head.next, lo->queue_head.prev,
                  &lo->queue_head);
            return 0;
      }
      return -EINVAL;
}

static 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;

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

      if (nbds_max > MAX_NBD) {
            printk(KERN_CRIT "nbd: cannot allocate more than %u nbds; %u requested.\n", MAX_NBD,
                        nbds_max);
            return -EINVAL;
      }

      for (i = 0; i < nbds_max; i++) {
            struct gendisk *disk = alloc_disk(1);
            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;
            }
      }

      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 = LO_MAGIC;
            nbd_dev[i].flags = 0;
            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);
            nbd_dev[i].blksize = 1024;
            nbd_dev[i].bytesize = 0;
            disk->major = NBD_MAJOR;
            disk->first_minor = i;
            disk->fops = &nbd_fops;
            disk->private_data = &nbd_dev[i];
            disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
            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);
      }
      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");
      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, "How many network block devices to initialize.");
#ifndef NDEBUG
module_param(debugflags, int, 0644);
MODULE_PARM_DESC(debugflags, "flags for controlling debug output");
#endif

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