2 * Network block device - make block devices work over TCP
4 * Note that you can not swap over this thing, yet. Seems to work but
5 * deadlocks sometimes - you can not swap over TCP in general.
7 * Copyright 1997-2000, 2008 Pavel Machek <pavel@ucw.cz>
8 * Parts copyright 2001 Steven Whitehouse <steve@chygwyn.com>
10 * This file is released under GPLv2 or later.
12 * (part of code stolen from loop.c)
15 #include <linux/major.h>
17 #include <linux/blkdev.h>
18 #include <linux/module.h>
19 #include <linux/init.h>
20 #include <linux/sched.h>
22 #include <linux/bio.h>
23 #include <linux/stat.h>
24 #include <linux/errno.h>
25 #include <linux/file.h>
26 #include <linux/ioctl.h>
27 #include <linux/mutex.h>
28 #include <linux/compiler.h>
29 #include <linux/err.h>
30 #include <linux/kernel.h>
31 #include <linux/slab.h>
33 #include <linux/net.h>
34 #include <linux/kthread.h>
36 #include <asm/uaccess.h>
37 #include <asm/types.h>
39 #include <linux/nbd.h>
41 #define NBD_MAGIC 0x68797548
44 #define dprintk(flags, fmt...)
46 #define dprintk(flags, fmt...) do { \
47 if (debugflags & (flags)) printk(KERN_DEBUG fmt); \
49 #define DBG_IOCTL 0x0004
50 #define DBG_INIT 0x0010
51 #define DBG_EXIT 0x0020
52 #define DBG_BLKDEV 0x0100
55 static unsigned int debugflags;
58 static unsigned int nbds_max = 16;
59 static struct nbd_device *nbd_dev;
63 * Use just one lock (or at most 1 per NIC). Two arguments for this:
64 * 1. Each NIC is essentially a synchronization point for all servers
65 * accessed through that NIC so there's no need to have more locks
67 * 2. More locks lead to more "Dirty cache line bouncing" which will slow
68 * down each lock to the point where they're actually slower than just
70 * Thanks go to Jens Axboe and Al Viro for their LKML emails explaining this!
72 static DEFINE_SPINLOCK(nbd_lock);
75 static const char *ioctl_cmd_to_ascii(int cmd)
78 case NBD_SET_SOCK: return "set-sock";
79 case NBD_SET_BLKSIZE: return "set-blksize";
80 case NBD_SET_SIZE: return "set-size";
81 case NBD_SET_TIMEOUT: return "set-timeout";
82 case NBD_SET_FLAGS: return "set-flags";
83 case NBD_DO_IT: return "do-it";
84 case NBD_CLEAR_SOCK: return "clear-sock";
85 case NBD_CLEAR_QUE: return "clear-que";
86 case NBD_PRINT_DEBUG: return "print-debug";
87 case NBD_SET_SIZE_BLOCKS: return "set-size-blocks";
88 case NBD_DISCONNECT: return "disconnect";
89 case BLKROSET: return "set-read-only";
90 case BLKFLSBUF: return "flush-buffer-cache";
95 static const char *nbdcmd_to_ascii(int cmd)
98 case NBD_CMD_READ: return "read";
99 case NBD_CMD_WRITE: return "write";
100 case NBD_CMD_DISC: return "disconnect";
101 case NBD_CMD_FLUSH: return "flush";
102 case NBD_CMD_TRIM: return "trim/discard";
108 static void nbd_end_request(struct request *req)
110 int error = req->errors ? -EIO : 0;
111 struct request_queue *q = req->q;
114 dprintk(DBG_BLKDEV, "%s: request %p: %s\n", req->rq_disk->disk_name,
115 req, error ? "failed" : "done");
117 spin_lock_irqsave(q->queue_lock, flags);
118 __blk_end_request_all(req, error);
119 spin_unlock_irqrestore(q->queue_lock, flags);
122 static void sock_shutdown(struct nbd_device *nbd, int lock)
124 /* Forcibly shutdown the socket causing all listeners
127 * FIXME: This code is duplicated from sys_shutdown, but
128 * there should be a more generic interface rather than
129 * calling socket ops directly here */
131 mutex_lock(&nbd->tx_lock);
133 dev_warn(disk_to_dev(nbd->disk), "shutting down socket\n");
134 kernel_sock_shutdown(nbd->sock, SHUT_RDWR);
138 mutex_unlock(&nbd->tx_lock);
141 static void nbd_xmit_timeout(unsigned long arg)
143 struct task_struct *task = (struct task_struct *)arg;
145 printk(KERN_WARNING "nbd: killing hung xmit (%s, pid: %d)\n",
146 task->comm, task->pid);
147 force_sig(SIGKILL, task);
151 * Send or receive packet.
153 static int sock_xmit(struct nbd_device *nbd, int send, void *buf, int size,
156 struct socket *sock = nbd->sock;
160 sigset_t blocked, oldset;
161 unsigned long pflags = current->flags;
163 if (unlikely(!sock)) {
164 dev_err(disk_to_dev(nbd->disk),
165 "Attempted %s on closed socket in sock_xmit\n",
166 (send ? "send" : "recv"));
170 /* Allow interception of SIGKILL only
171 * Don't allow other signals to interrupt the transmission */
172 siginitsetinv(&blocked, sigmask(SIGKILL));
173 sigprocmask(SIG_SETMASK, &blocked, &oldset);
175 current->flags |= PF_MEMALLOC;
177 sock->sk->sk_allocation = GFP_NOIO | __GFP_MEMALLOC;
182 msg.msg_control = NULL;
183 msg.msg_controllen = 0;
184 msg.msg_flags = msg_flags | MSG_NOSIGNAL;
187 struct timer_list ti;
189 if (nbd->xmit_timeout) {
191 ti.function = nbd_xmit_timeout;
192 ti.data = (unsigned long)current;
193 ti.expires = jiffies + nbd->xmit_timeout;
196 result = kernel_sendmsg(sock, &msg, &iov, 1, size);
197 if (nbd->xmit_timeout)
200 result = kernel_recvmsg(sock, &msg, &iov, 1, size,
203 if (signal_pending(current)) {
205 printk(KERN_WARNING "nbd (pid %d: %s) got signal %d\n",
206 task_pid_nr(current), current->comm,
207 dequeue_signal_lock(current, ¤t->blocked, &info));
209 sock_shutdown(nbd, !send);
215 result = -EPIPE; /* short read */
222 sigprocmask(SIG_SETMASK, &oldset, NULL);
223 tsk_restore_flags(current, pflags, PF_MEMALLOC);
228 static inline int sock_send_bvec(struct nbd_device *nbd, struct bio_vec *bvec,
232 void *kaddr = kmap(bvec->bv_page);
233 result = sock_xmit(nbd, 1, kaddr + bvec->bv_offset,
234 bvec->bv_len, flags);
235 kunmap(bvec->bv_page);
239 /* always call with the tx_lock held */
240 static int nbd_send_req(struct nbd_device *nbd, struct request *req)
243 struct nbd_request request;
244 unsigned long size = blk_rq_bytes(req);
246 memset(&request, 0, sizeof(request));
247 request.magic = htonl(NBD_REQUEST_MAGIC);
248 request.type = htonl(nbd_cmd(req));
250 if (nbd_cmd(req) != NBD_CMD_FLUSH && nbd_cmd(req) != NBD_CMD_DISC) {
251 request.from = cpu_to_be64((u64)blk_rq_pos(req) << 9);
252 request.len = htonl(size);
254 memcpy(request.handle, &req, sizeof(req));
256 dprintk(DBG_TX, "%s: request %p: sending control (%s@%llu,%uB)\n",
257 nbd->disk->disk_name, req,
258 nbdcmd_to_ascii(nbd_cmd(req)),
259 (unsigned long long)blk_rq_pos(req) << 9,
261 result = sock_xmit(nbd, 1, &request, sizeof(request),
262 (nbd_cmd(req) == NBD_CMD_WRITE) ? MSG_MORE : 0);
264 dev_err(disk_to_dev(nbd->disk),
265 "Send control failed (result %d)\n", result);
269 if (nbd_cmd(req) == NBD_CMD_WRITE) {
270 struct req_iterator iter;
273 * we are really probing at internals to determine
274 * whether to set MSG_MORE or not...
276 rq_for_each_segment(bvec, req, iter) {
278 if (!rq_iter_last(bvec, iter))
280 dprintk(DBG_TX, "%s: request %p: sending %d bytes data\n",
281 nbd->disk->disk_name, req, bvec.bv_len);
282 result = sock_send_bvec(nbd, &bvec, flags);
284 dev_err(disk_to_dev(nbd->disk),
285 "Send data failed (result %d)\n",
297 static struct request *nbd_find_request(struct nbd_device *nbd,
298 struct request *xreq)
300 struct request *req, *tmp;
303 err = wait_event_interruptible(nbd->active_wq, nbd->active_req != xreq);
307 spin_lock(&nbd->queue_lock);
308 list_for_each_entry_safe(req, tmp, &nbd->queue_head, queuelist) {
311 list_del_init(&req->queuelist);
312 spin_unlock(&nbd->queue_lock);
315 spin_unlock(&nbd->queue_lock);
323 static inline int sock_recv_bvec(struct nbd_device *nbd, struct bio_vec *bvec)
326 void *kaddr = kmap(bvec->bv_page);
327 result = sock_xmit(nbd, 0, kaddr + bvec->bv_offset, bvec->bv_len,
329 kunmap(bvec->bv_page);
333 /* NULL returned = something went wrong, inform userspace */
334 static struct request *nbd_read_stat(struct nbd_device *nbd)
337 struct nbd_reply reply;
341 result = sock_xmit(nbd, 0, &reply, sizeof(reply), MSG_WAITALL);
343 dev_err(disk_to_dev(nbd->disk),
344 "Receive control failed (result %d)\n", result);
348 if (ntohl(reply.magic) != NBD_REPLY_MAGIC) {
349 dev_err(disk_to_dev(nbd->disk), "Wrong magic (0x%lx)\n",
350 (unsigned long)ntohl(reply.magic));
355 req = nbd_find_request(nbd, *(struct request **)reply.handle);
357 result = PTR_ERR(req);
358 if (result != -ENOENT)
361 dev_err(disk_to_dev(nbd->disk), "Unexpected reply (%p)\n",
367 if (ntohl(reply.error)) {
368 dev_err(disk_to_dev(nbd->disk), "Other side returned error (%d)\n",
374 dprintk(DBG_RX, "%s: request %p: got reply\n",
375 nbd->disk->disk_name, req);
376 if (nbd_cmd(req) == NBD_CMD_READ) {
377 struct req_iterator iter;
380 rq_for_each_segment(bvec, req, iter) {
381 result = sock_recv_bvec(nbd, &bvec);
383 dev_err(disk_to_dev(nbd->disk), "Receive data failed (result %d)\n",
388 dprintk(DBG_RX, "%s: request %p: got %d bytes data\n",
389 nbd->disk->disk_name, req, bvec.bv_len);
394 nbd->harderror = result;
398 static ssize_t pid_show(struct device *dev,
399 struct device_attribute *attr, char *buf)
401 struct gendisk *disk = dev_to_disk(dev);
403 return sprintf(buf, "%ld\n",
404 (long) ((struct nbd_device *)disk->private_data)->pid);
407 static struct device_attribute pid_attr = {
408 .attr = { .name = "pid", .mode = S_IRUGO},
412 static int nbd_do_it(struct nbd_device *nbd)
417 BUG_ON(nbd->magic != NBD_MAGIC);
419 sk_set_memalloc(nbd->sock->sk);
420 nbd->pid = task_pid_nr(current);
421 ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
423 dev_err(disk_to_dev(nbd->disk), "device_create_file failed!\n");
428 while ((req = nbd_read_stat(nbd)) != NULL)
429 nbd_end_request(req);
431 device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
436 static void nbd_clear_que(struct nbd_device *nbd)
440 BUG_ON(nbd->magic != NBD_MAGIC);
443 * Because we have set nbd->sock to NULL under the tx_lock, all
444 * modifications to the list must have completed by now. For
445 * the same reason, the active_req must be NULL.
447 * As a consequence, we don't need to take the spin lock while
448 * purging the list here.
451 BUG_ON(nbd->active_req);
453 while (!list_empty(&nbd->queue_head)) {
454 req = list_entry(nbd->queue_head.next, struct request,
456 list_del_init(&req->queuelist);
458 nbd_end_request(req);
461 while (!list_empty(&nbd->waiting_queue)) {
462 req = list_entry(nbd->waiting_queue.next, struct request,
464 list_del_init(&req->queuelist);
466 nbd_end_request(req);
471 static void nbd_handle_req(struct nbd_device *nbd, struct request *req)
473 if (req->cmd_type != REQ_TYPE_FS)
476 nbd_cmd(req) = NBD_CMD_READ;
477 if (rq_data_dir(req) == WRITE) {
478 if ((req->cmd_flags & REQ_DISCARD)) {
479 WARN_ON(!(nbd->flags & NBD_FLAG_SEND_TRIM));
480 nbd_cmd(req) = NBD_CMD_TRIM;
482 nbd_cmd(req) = NBD_CMD_WRITE;
483 if (nbd->flags & NBD_FLAG_READ_ONLY) {
484 dev_err(disk_to_dev(nbd->disk),
485 "Write on read-only\n");
490 if (req->cmd_flags & REQ_FLUSH) {
491 BUG_ON(unlikely(blk_rq_sectors(req)));
492 nbd_cmd(req) = NBD_CMD_FLUSH;
497 mutex_lock(&nbd->tx_lock);
498 if (unlikely(!nbd->sock)) {
499 mutex_unlock(&nbd->tx_lock);
500 dev_err(disk_to_dev(nbd->disk),
501 "Attempted send on closed socket\n");
505 nbd->active_req = req;
507 if (nbd_send_req(nbd, req) != 0) {
508 dev_err(disk_to_dev(nbd->disk), "Request send failed\n");
510 nbd_end_request(req);
512 spin_lock(&nbd->queue_lock);
513 list_add_tail(&req->queuelist, &nbd->queue_head);
514 spin_unlock(&nbd->queue_lock);
517 nbd->active_req = NULL;
518 mutex_unlock(&nbd->tx_lock);
519 wake_up_all(&nbd->active_wq);
525 nbd_end_request(req);
528 static int nbd_thread(void *data)
530 struct nbd_device *nbd = data;
533 set_user_nice(current, MIN_NICE);
534 while (!kthread_should_stop() || !list_empty(&nbd->waiting_queue)) {
535 /* wait for something to do */
536 wait_event_interruptible(nbd->waiting_wq,
537 kthread_should_stop() ||
538 !list_empty(&nbd->waiting_queue));
540 /* extract request */
541 if (list_empty(&nbd->waiting_queue))
544 spin_lock_irq(&nbd->queue_lock);
545 req = list_entry(nbd->waiting_queue.next, struct request,
547 list_del_init(&req->queuelist);
548 spin_unlock_irq(&nbd->queue_lock);
551 nbd_handle_req(nbd, req);
557 * We always wait for result of write, for now. It would be nice to make it optional
559 * if ((rq_data_dir(req) == WRITE) && (nbd->flags & NBD_WRITE_NOCHK))
560 * { printk( "Warning: Ignoring result!\n"); nbd_end_request( req ); }
563 static void do_nbd_request(struct request_queue *q)
564 __releases(q->queue_lock) __acquires(q->queue_lock)
568 while ((req = blk_fetch_request(q)) != NULL) {
569 struct nbd_device *nbd;
571 spin_unlock_irq(q->queue_lock);
573 dprintk(DBG_BLKDEV, "%s: request %p: dequeued (flags=%x)\n",
574 req->rq_disk->disk_name, req, req->cmd_type);
576 nbd = req->rq_disk->private_data;
578 BUG_ON(nbd->magic != NBD_MAGIC);
580 if (unlikely(!nbd->sock)) {
581 dev_err(disk_to_dev(nbd->disk),
582 "Attempted send on closed socket\n");
584 nbd_end_request(req);
585 spin_lock_irq(q->queue_lock);
589 spin_lock_irq(&nbd->queue_lock);
590 list_add_tail(&req->queuelist, &nbd->waiting_queue);
591 spin_unlock_irq(&nbd->queue_lock);
593 wake_up(&nbd->waiting_wq);
595 spin_lock_irq(q->queue_lock);
599 /* Must be called with tx_lock held */
601 static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
602 unsigned int cmd, unsigned long arg)
605 case NBD_DISCONNECT: {
608 dev_info(disk_to_dev(nbd->disk), "NBD_DISCONNECT\n");
612 mutex_unlock(&nbd->tx_lock);
614 mutex_lock(&nbd->tx_lock);
615 blk_rq_init(NULL, &sreq);
616 sreq.cmd_type = REQ_TYPE_SPECIAL;
617 nbd_cmd(&sreq) = NBD_CMD_DISC;
619 /* Check again after getting mutex back. */
625 nbd_send_req(nbd, &sreq);
629 case NBD_CLEAR_SOCK: {
630 struct socket *sock = nbd->sock;
633 BUG_ON(!list_empty(&nbd->queue_head));
634 BUG_ON(!list_empty(&nbd->waiting_queue));
646 sock = sockfd_lookup(arg, &err);
650 bdev->bd_invalidated = 1;
651 nbd->disconnect = 0; /* we're connected now */
657 case NBD_SET_BLKSIZE:
659 nbd->bytesize &= ~(nbd->blksize-1);
660 bdev->bd_inode->i_size = nbd->bytesize;
661 set_blocksize(bdev, nbd->blksize);
662 set_capacity(nbd->disk, nbd->bytesize >> 9);
666 nbd->bytesize = arg & ~(nbd->blksize-1);
667 bdev->bd_inode->i_size = nbd->bytesize;
668 set_blocksize(bdev, nbd->blksize);
669 set_capacity(nbd->disk, nbd->bytesize >> 9);
672 case NBD_SET_TIMEOUT:
673 nbd->xmit_timeout = arg * HZ;
680 case NBD_SET_SIZE_BLOCKS:
681 nbd->bytesize = ((u64) arg) * nbd->blksize;
682 bdev->bd_inode->i_size = nbd->bytesize;
683 set_blocksize(bdev, nbd->blksize);
684 set_capacity(nbd->disk, nbd->bytesize >> 9);
688 struct task_struct *thread;
697 mutex_unlock(&nbd->tx_lock);
699 if (nbd->flags & NBD_FLAG_READ_ONLY)
700 set_device_ro(bdev, true);
701 if (nbd->flags & NBD_FLAG_SEND_TRIM)
702 queue_flag_set_unlocked(QUEUE_FLAG_DISCARD,
704 if (nbd->flags & NBD_FLAG_SEND_FLUSH)
705 blk_queue_flush(nbd->disk->queue, REQ_FLUSH);
707 blk_queue_flush(nbd->disk->queue, 0);
709 thread = kthread_create(nbd_thread, nbd, "%s",
710 nbd->disk->disk_name);
711 if (IS_ERR(thread)) {
712 mutex_lock(&nbd->tx_lock);
713 return PTR_ERR(thread);
715 wake_up_process(thread);
716 error = nbd_do_it(nbd);
717 kthread_stop(thread);
719 mutex_lock(&nbd->tx_lock);
722 sock_shutdown(nbd, 0);
726 dev_warn(disk_to_dev(nbd->disk), "queue cleared\n");
728 queue_flag_clear_unlocked(QUEUE_FLAG_DISCARD, nbd->disk->queue);
729 set_device_ro(bdev, false);
734 bdev->bd_inode->i_size = 0;
735 set_capacity(nbd->disk, 0);
737 ioctl_by_bdev(bdev, BLKRRPART, 0);
738 if (nbd->disconnect) /* user requested, ignore socket errors */
740 return nbd->harderror;
745 * This is for compatibility only. The queue is always cleared
746 * by NBD_DO_IT or NBD_CLEAR_SOCK.
750 case NBD_PRINT_DEBUG:
751 dev_info(disk_to_dev(nbd->disk),
752 "next = %p, prev = %p, head = %p\n",
753 nbd->queue_head.next, nbd->queue_head.prev,
760 static int nbd_ioctl(struct block_device *bdev, fmode_t mode,
761 unsigned int cmd, unsigned long arg)
763 struct nbd_device *nbd = bdev->bd_disk->private_data;
766 if (!capable(CAP_SYS_ADMIN))
769 BUG_ON(nbd->magic != NBD_MAGIC);
771 /* Anyone capable of this syscall can do *real bad* things */
772 dprintk(DBG_IOCTL, "%s: nbd_ioctl cmd=%s(0x%x) arg=%lu\n",
773 nbd->disk->disk_name, ioctl_cmd_to_ascii(cmd), cmd, arg);
775 mutex_lock(&nbd->tx_lock);
776 error = __nbd_ioctl(bdev, nbd, cmd, arg);
777 mutex_unlock(&nbd->tx_lock);
782 static const struct block_device_operations nbd_fops =
784 .owner = THIS_MODULE,
789 * And here should be modules and kernel interface
790 * (Just smiley confuses emacs :-)
793 static int __init nbd_init(void)
799 BUILD_BUG_ON(sizeof(struct nbd_request) != 28);
802 printk(KERN_ERR "nbd: max_part must be >= 0\n");
806 nbd_dev = kcalloc(nbds_max, sizeof(*nbd_dev), GFP_KERNEL);
812 part_shift = fls(max_part);
815 * Adjust max_part according to part_shift as it is exported
816 * to user space so that user can know the max number of
817 * partition kernel should be able to manage.
819 * Note that -1 is required because partition 0 is reserved
820 * for the whole disk.
822 max_part = (1UL << part_shift) - 1;
825 if ((1UL << part_shift) > DISK_MAX_PARTS)
828 if (nbds_max > 1UL << (MINORBITS - part_shift))
831 for (i = 0; i < nbds_max; i++) {
832 struct gendisk *disk = alloc_disk(1 << part_shift);
835 nbd_dev[i].disk = disk;
837 * The new linux 2.5 block layer implementation requires
838 * every gendisk to have its very own request_queue struct.
839 * These structs are big so we dynamically allocate them.
841 disk->queue = blk_init_queue(do_nbd_request, &nbd_lock);
847 * Tell the block layer that we are not a rotational device
849 queue_flag_set_unlocked(QUEUE_FLAG_NONROT, disk->queue);
850 disk->queue->limits.discard_granularity = 512;
851 disk->queue->limits.max_discard_sectors = UINT_MAX;
852 disk->queue->limits.discard_zeroes_data = 0;
853 blk_queue_max_hw_sectors(disk->queue, 65536);
854 disk->queue->limits.max_sectors = 256;
857 if (register_blkdev(NBD_MAJOR, "nbd")) {
862 printk(KERN_INFO "nbd: registered device at major %d\n", NBD_MAJOR);
863 dprintk(DBG_INIT, "nbd: debugflags=0x%x\n", debugflags);
865 for (i = 0; i < nbds_max; i++) {
866 struct gendisk *disk = nbd_dev[i].disk;
867 nbd_dev[i].magic = NBD_MAGIC;
868 INIT_LIST_HEAD(&nbd_dev[i].waiting_queue);
869 spin_lock_init(&nbd_dev[i].queue_lock);
870 INIT_LIST_HEAD(&nbd_dev[i].queue_head);
871 mutex_init(&nbd_dev[i].tx_lock);
872 init_waitqueue_head(&nbd_dev[i].active_wq);
873 init_waitqueue_head(&nbd_dev[i].waiting_wq);
874 nbd_dev[i].blksize = 1024;
875 nbd_dev[i].bytesize = 0;
876 disk->major = NBD_MAJOR;
877 disk->first_minor = i << part_shift;
878 disk->fops = &nbd_fops;
879 disk->private_data = &nbd_dev[i];
880 sprintf(disk->disk_name, "nbd%d", i);
881 set_capacity(disk, 0);
888 blk_cleanup_queue(nbd_dev[i].disk->queue);
889 put_disk(nbd_dev[i].disk);
895 static void __exit nbd_cleanup(void)
898 for (i = 0; i < nbds_max; i++) {
899 struct gendisk *disk = nbd_dev[i].disk;
900 nbd_dev[i].magic = 0;
903 blk_cleanup_queue(disk->queue);
907 unregister_blkdev(NBD_MAJOR, "nbd");
909 printk(KERN_INFO "nbd: unregistered device at major %d\n", NBD_MAJOR);
912 module_init(nbd_init);
913 module_exit(nbd_cleanup);
915 MODULE_DESCRIPTION("Network Block Device");
916 MODULE_LICENSE("GPL");
918 module_param(nbds_max, int, 0444);
919 MODULE_PARM_DESC(nbds_max, "number of network block devices to initialize (default: 16)");
920 module_param(max_part, int, 0444);
921 MODULE_PARM_DESC(max_part, "number of partitions per device (default: 0)");
923 module_param(debugflags, int, 0644);
924 MODULE_PARM_DESC(debugflags, "flags for controlling debug output");