4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License version 2 only,
8 * as published by the Free Software Foundation.
10 * This program is distributed in the hope that it will be useful, but
11 * WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 * General Public License version 2 for more details (a copy is included
14 * in the LICENSE file that accompanied this code).
16 * You should have received a copy of the GNU General Public License
17 * version 2 along with this program; If not, see
18 * http://www.sun.com/software/products/lustre/docs/GPLv2.pdf
20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
21 * CA 95054 USA or visit www.sun.com if you need additional information or
27 * Copyright (c) 2007, 2010, Oracle and/or its affiliates. All rights reserved.
28 * Use is subject to license terms.
30 * Copyright (c) 2011, 2013, Intel Corporation.
33 * This file is part of Lustre, http://www.lustre.org/
34 * Lustre is a trademark of Sun Microsystems, Inc.
38 * linux/drivers/block/loop.c
40 * Written by Theodore Ts'o, 3/29/93
42 * Copyright 1993 by Theodore Ts'o. Redistribution of this file is
43 * permitted under the GNU General Public License.
45 * Modularized and updated for 1.1.16 kernel - Mitch Dsouza 28th May 1994
46 * Adapted for 1.3.59 kernel - Andries Brouwer, 1 Feb 1996
48 * Fixed do_loop_request() re-entrancy - Vincent.Renardias@waw.com Mar 20, 1997
50 * Added devfs support - Richard Gooch <rgooch@atnf.csiro.au> 16-Jan-1998
52 * Handle sparse backing files correctly - Kenn Humborg, Jun 28, 1998
54 * Loadable modules and other fixes by AK, 1998
56 * Maximum number of loop devices now dynamic via max_loop module parameter.
57 * Russell Kroll <rkroll@exploits.org> 19990701
59 * Maximum number of loop devices when compiled-in now selectable by passing
60 * max_loop=<1-255> to the kernel on boot.
61 * Erik I. Bols?, <eriki@himolde.no>, Oct 31, 1999
63 * Completely rewrite request handling to be make_request_fn style and
64 * non blocking, pushing work to a helper thread. Lots of fixes from
66 * Jens Axboe <axboe@suse.de>, Nov 2000
68 * Support up to 256 loop devices
69 * Heinz Mauelshagen <mge@sistina.com>, Feb 2002
71 * Support for falling back on the write file operation when the address space
72 * operations prepare_write and/or commit_write are not available on the
74 * Anton Altaparmakov, 16 Feb 2005
77 * - Advisory locking is ignored here.
78 * - Should use an own CAP_* category instead of CAP_SYS_ADMIN
82 #include <linux/module.h>
84 #include <linux/sched.h>
86 #include <linux/file.h>
87 #include <linux/stat.h>
88 #include <linux/errno.h>
89 #include <linux/major.h>
90 #include <linux/wait.h>
91 #include <linux/blkdev.h>
92 #include <linux/blkpg.h>
93 #include <linux/init.h>
94 #include <linux/swap.h>
95 #include <linux/slab.h>
96 #include <linux/suspend.h>
97 #include <linux/writeback.h>
98 #include <linux/buffer_head.h> /* for invalidate_bdev() */
99 #include <linux/completion.h>
100 #include <linux/highmem.h>
101 #include <linux/gfp.h>
102 #include <linux/swap.h>
103 #include <linux/pagevec.h>
105 #include <asm/uaccess.h>
107 #include <lustre_lib.h>
108 #include <lustre_lite.h>
109 #include "llite_internal.h"
111 #define LLOOP_MAX_SEGMENTS LNET_MAX_IOV
113 /* Possible states of device */
120 struct lloop_device {
126 struct file *lo_backing_file;
127 struct block_device *lo_device;
128 unsigned lo_blocksize;
134 struct bio *lo_biotail;
136 struct semaphore lo_sem;
137 struct mutex lo_ctl_mutex;
139 wait_queue_head_t lo_bh_wait;
141 struct request_queue *lo_queue;
143 const struct lu_env *lo_env;
145 struct ll_dio_pages lo_pvec;
147 /* data to handle bio for lustre. */
148 struct lo_request_data {
149 struct page *lrd_pages[LLOOP_MAX_SEGMENTS];
150 loff_t lrd_offsets[LLOOP_MAX_SEGMENTS];
158 LO_FLAGS_READ_ONLY = 1,
161 static int lloop_major;
162 #define MAX_LOOP_DEFAULT 16
163 static int max_loop = MAX_LOOP_DEFAULT;
164 static struct lloop_device *loop_dev;
165 static struct gendisk **disks;
166 static struct mutex lloop_mutex;
167 static void *ll_iocontrol_magic = NULL;
169 static loff_t get_loop_size(struct lloop_device *lo, struct file *file)
171 loff_t size, offset, loopsize;
173 /* Compute loopsize in bytes */
174 size = i_size_read(file->f_mapping->host);
175 offset = lo->lo_offset;
176 loopsize = size - offset;
177 if (lo->lo_sizelimit > 0 && lo->lo_sizelimit < loopsize)
178 loopsize = lo->lo_sizelimit;
181 * Unfortunately, if we want to do I/O on the device,
182 * the number of 512-byte sectors has to fit into a sector_t.
184 return loopsize >> 9;
187 static int do_bio_lustrebacked(struct lloop_device *lo, struct bio *head)
189 const struct lu_env *env = lo->lo_env;
190 struct cl_io *io = &lo->lo_io;
191 struct inode *inode = lo->lo_backing_file->f_dentry->d_inode;
192 struct cl_object *obj = ll_i2info(inode)->lli_clob;
195 #ifdef HAVE_BVEC_ITER
196 struct bvec_iter iter;
200 struct bio_vec *bvec;
203 obd_count page_count = 0;
207 struct ll_dio_pages *pvec = &lo->lo_pvec;
208 struct page **pages = pvec->ldp_pages;
209 loff_t *offsets = pvec->ldp_offsets;
211 truncate_inode_pages(inode->i_mapping, 0);
213 /* initialize the IO */
214 memset(io, 0, sizeof(*io));
216 ret = cl_io_init(env, io, CIT_MISC, obj);
218 return io->ci_result;
219 io->ci_lockreq = CILR_NEVER;
221 LASSERT(head != NULL);
223 for (bio = head; bio != NULL; bio = bio->bi_next) {
224 LASSERT(rw == bio->bi_rw);
226 #ifdef HAVE_BVEC_ITER
227 offset = (pgoff_t)(bio->bi_iter.bi_sector << 9) + lo->lo_offset;
228 bio_for_each_segment(bvec, bio, iter) {
229 BUG_ON(bvec.bv_offset != 0);
230 BUG_ON(bvec.bv_len != PAGE_CACHE_SIZE);
232 pages[page_count] = bvec.bv_page;
233 offsets[page_count] = offset;
235 offset += bvec.bv_len;
237 offset = (pgoff_t)(bio->bi_sector << 9) + lo->lo_offset;
238 bio_for_each_segment(bvec, bio, iter) {
239 BUG_ON(bvec->bv_offset != 0);
240 BUG_ON(bvec->bv_len != PAGE_CACHE_SIZE);
242 pages[page_count] = bvec->bv_page;
243 offsets[page_count] = offset;
245 offset += bvec->bv_len;
248 LASSERT(page_count <= LLOOP_MAX_SEGMENTS);
251 ll_stats_ops_tally(ll_i2sbi(inode),
252 (rw == WRITE) ? LPROC_LL_BRW_WRITE : LPROC_LL_BRW_READ,
255 pvec->ldp_size = page_count << PAGE_CACHE_SHIFT;
256 pvec->ldp_nr = page_count;
258 /* FIXME: in ll_direct_rw_pages, it has to allocate many cl_page{}s to
259 * write those pages into OST. Even worse case is that more pages
260 * would be asked to write out to swap space, and then finally get here
262 * Unfortunately this is NOT easy to fix.
263 * Thoughts on solution:
264 * 0. Define a reserved pool for cl_pages, which could be a list of
265 * pre-allocated cl_pages;
266 * 1. Define a new operation in cl_object_operations{}, says clo_depth,
267 * which measures how many layers for this lustre object. Generally
268 * speaking, the depth would be 2, one for llite, and one for lovsub.
269 * However, for SNS, there will be more since we need additional page
271 * 2. Reserve the # of (page_count * depth) cl_pages from the reserved
272 * pool. Afterwards, the clio would allocate the pages from reserved
273 * pool, this guarantees we neeedn't allocate the cl_pages from
274 * generic cl_page slab cache.
275 * Of course, if there is NOT enough pages in the pool, we might
276 * be asked to write less pages once, this purely depends on
277 * implementation. Anyway, we should be careful to avoid deadlocking.
279 mutex_lock(&inode->i_mutex);
280 bytes = ll_direct_rw_pages(env, io, rw, inode, pvec);
281 mutex_unlock(&inode->i_mutex);
283 return (bytes == pvec->ldp_size) ? 0 : (int)bytes;
287 * Add bio to back of pending list
289 static void loop_add_bio(struct lloop_device *lo, struct bio *bio)
293 spin_lock_irqsave(&lo->lo_lock, flags);
294 if (lo->lo_biotail) {
295 lo->lo_biotail->bi_next = bio;
296 lo->lo_biotail = bio;
298 lo->lo_bio = lo->lo_biotail = bio;
299 spin_unlock_irqrestore(&lo->lo_lock, flags);
301 atomic_inc(&lo->lo_pending);
302 if (waitqueue_active(&lo->lo_bh_wait))
303 wake_up(&lo->lo_bh_wait);
307 * Grab first pending buffer
309 static unsigned int loop_get_bio(struct lloop_device *lo, struct bio **req)
313 unsigned int count = 0;
314 unsigned int page_count = 0;
317 spin_lock_irq(&lo->lo_lock);
319 if (unlikely(first == NULL)) {
320 spin_unlock_irq(&lo->lo_lock);
324 /* TODO: need to split the bio, too bad. */
325 LASSERT(first->bi_vcnt <= LLOOP_MAX_SEGMENTS);
329 while (*bio && (*bio)->bi_rw == rw) {
330 #ifdef HAVE_BVEC_ITER
331 CDEBUG(D_INFO, "bio sector %llu size %u count %u vcnt%u \n",
332 (unsigned long long)(*bio)->bi_iter.bi_sector,
333 (*bio)->bi_iter.bi_size, page_count, (*bio)->bi_vcnt);
335 CDEBUG(D_INFO, "bio sector %llu size %u count %u vcnt%u \n",
336 (unsigned long long)(*bio)->bi_sector, (*bio)->bi_size,
337 page_count, (*bio)->bi_vcnt);
339 if (page_count + (*bio)->bi_vcnt > LLOOP_MAX_SEGMENTS)
342 page_count += (*bio)->bi_vcnt;
344 bio = &(*bio)->bi_next;
347 /* Some of bios can't be mergable. */
351 /* Hit the end of queue */
352 lo->lo_biotail = NULL;
356 spin_unlock_irq(&lo->lo_lock);
361 loop_make_request(struct request_queue *q, struct bio *old_bio)
363 struct lloop_device *lo = q->queuedata;
364 int rw = bio_rw(old_bio);
370 #ifdef HAVE_BVEC_ITER
371 CDEBUG(D_INFO, "submit bio sector %llu size %u\n",
372 (unsigned long long)old_bio->bi_iter.bi_sector,
373 old_bio->bi_iter.bi_size);
375 CDEBUG(D_INFO, "submit bio sector %llu size %u\n",
376 (unsigned long long)old_bio->bi_sector, old_bio->bi_size);
379 spin_lock_irq(&lo->lo_lock);
380 inactive = (lo->lo_state != LLOOP_BOUND);
381 spin_unlock_irq(&lo->lo_lock);
386 if (lo->lo_flags & LO_FLAGS_READ_ONLY)
388 } else if (rw == READA) {
390 } else if (rw != READ) {
391 CERROR("lloop: unknown command (%x)\n", rw);
394 loop_add_bio(lo, old_bio);
397 bio_io_error(old_bio);
401 #ifdef HAVE_REQUEST_QUEUE_UNPLUG_FN
403 * kick off io on the underlying address space
405 static void loop_unplug(struct request_queue *q)
407 struct lloop_device *lo = q->queuedata;
409 clear_bit(QUEUE_FLAG_PLUGGED, &q->queue_flags);
410 blk_run_address_space(lo->lo_backing_file->f_mapping);
414 static inline void loop_handle_bio(struct lloop_device *lo, struct bio *bio)
417 ret = do_bio_lustrebacked(lo, bio);
419 struct bio *tmp = bio->bi_next;
426 static inline int loop_active(struct lloop_device *lo)
428 return atomic_read(&lo->lo_pending) ||
429 (lo->lo_state == LLOOP_RUNDOWN);
433 * worker thread that handles reads/writes to file backed loop devices,
434 * to avoid blocking in our make_request_fn.
436 static int loop_thread(void *data)
438 struct lloop_device *lo = data;
441 unsigned long times = 0;
442 unsigned long total_count = 0;
448 set_user_nice(current, -20);
450 lo->lo_state = LLOOP_BOUND;
452 env = cl_env_get(&refcheck);
454 GOTO(out, ret = PTR_ERR(env));
457 memset(&lo->lo_pvec, 0, sizeof(lo->lo_pvec));
458 lo->lo_pvec.ldp_pages = lo->lo_requests[0].lrd_pages;
459 lo->lo_pvec.ldp_offsets = lo->lo_requests[0].lrd_offsets;
462 * up sem, we are running
467 wait_event(lo->lo_bh_wait, loop_active(lo));
468 if (!atomic_read(&lo->lo_pending)) {
470 spin_lock_irq(&lo->lo_lock);
471 exiting = (lo->lo_state == LLOOP_RUNDOWN);
472 spin_unlock_irq(&lo->lo_lock);
478 count = loop_get_bio(lo, &bio);
480 CWARN("lloop(minor: %d): missing bio\n", lo->lo_number);
484 total_count += count;
485 if (total_count < count) { /* overflow */
491 if ((times & 127) == 0) {
492 CDEBUG(D_INFO, "total: %lu, count: %lu, avg: %lu\n",
493 total_count, times, total_count / times);
496 LASSERT(bio != NULL);
497 LASSERT(count <= atomic_read(&lo->lo_pending));
498 loop_handle_bio(lo, bio);
499 atomic_sub(count, &lo->lo_pending);
501 cl_env_put(env, &refcheck);
508 static int loop_set_fd(struct lloop_device *lo, struct file *unused,
509 struct block_device *bdev, struct file *file)
512 struct address_space *mapping;
517 if (!try_module_get(THIS_MODULE))
521 if (lo->lo_state != LLOOP_UNBOUND)
524 mapping = file->f_mapping;
525 inode = mapping->host;
528 if (!S_ISREG(inode->i_mode) || inode->i_sb->s_magic != LL_SUPER_MAGIC)
531 if (!(file->f_mode & FMODE_WRITE))
532 lo_flags |= LO_FLAGS_READ_ONLY;
534 size = get_loop_size(lo, file);
536 if ((loff_t)(sector_t)size != size) {
541 /* remove all pages in cache so as dirty pages not to be existent. */
542 truncate_inode_pages(mapping, 0);
544 set_device_ro(bdev, (lo_flags & LO_FLAGS_READ_ONLY) != 0);
546 lo->lo_blocksize = PAGE_CACHE_SIZE;
547 lo->lo_device = bdev;
548 lo->lo_flags = lo_flags;
549 lo->lo_backing_file = file;
550 lo->lo_sizelimit = 0;
551 lo->old_gfp_mask = mapping_gfp_mask(mapping);
552 mapping_set_gfp_mask(mapping, lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
554 lo->lo_bio = lo->lo_biotail = NULL;
557 * set queue make_request_fn, and add limits based on lower level
560 blk_queue_make_request(lo->lo_queue, loop_make_request);
561 lo->lo_queue->queuedata = lo;
562 #ifdef HAVE_REQUEST_QUEUE_UNPLUG_FN
563 lo->lo_queue->unplug_fn = loop_unplug;
566 /* queue parameters */
567 blk_queue_max_hw_sectors(lo->lo_queue,
568 LLOOP_MAX_SEGMENTS << (PAGE_CACHE_SHIFT - 9));
569 blk_queue_max_segments(lo->lo_queue, LLOOP_MAX_SEGMENTS);
571 set_capacity(disks[lo->lo_number], size);
572 bd_set_size(bdev, size << 9);
574 set_blocksize(bdev, lo->lo_blocksize);
576 kthread_run(loop_thread, lo, "lloop%d", lo->lo_number);
581 /* This is safe: open() is still holding a reference. */
582 module_put(THIS_MODULE);
586 static int loop_clr_fd(struct lloop_device *lo, struct block_device *bdev,
589 struct file *filp = lo->lo_backing_file;
590 int gfp = lo->old_gfp_mask;
592 if (lo->lo_state != LLOOP_BOUND)
595 if (lo->lo_refcnt > count) /* we needed one fd for the ioctl */
601 spin_lock_irq(&lo->lo_lock);
602 lo->lo_state = LLOOP_RUNDOWN;
603 spin_unlock_irq(&lo->lo_lock);
604 wake_up(&lo->lo_bh_wait);
607 lo->lo_backing_file = NULL;
608 lo->lo_device = NULL;
610 lo->lo_sizelimit = 0;
612 invalidate_bdev(bdev);
613 set_capacity(disks[lo->lo_number], 0);
614 bd_set_size(bdev, 0);
615 mapping_set_gfp_mask(filp->f_mapping, gfp);
616 lo->lo_state = LLOOP_UNBOUND;
618 /* This is safe: open() is still holding a reference. */
619 module_put(THIS_MODULE);
623 static int lo_open(struct block_device *bdev, fmode_t mode)
625 struct lloop_device *lo = bdev->bd_disk->private_data;
627 mutex_lock(&lo->lo_ctl_mutex);
629 mutex_unlock(&lo->lo_ctl_mutex);
634 #ifdef HAVE_BLKDEV_RELEASE_RETURN_INT
639 lo_release(struct gendisk *disk, fmode_t mode)
641 struct lloop_device *lo = disk->private_data;
643 mutex_lock(&lo->lo_ctl_mutex);
645 mutex_unlock(&lo->lo_ctl_mutex);
646 #ifdef HAVE_BLKDEV_RELEASE_RETURN_INT
651 /* lloop device node's ioctl function. */
652 static int lo_ioctl(struct block_device *bdev, fmode_t mode,
653 unsigned int cmd, unsigned long arg)
655 struct lloop_device *lo = bdev->bd_disk->private_data;
656 struct inode *inode = NULL;
659 mutex_lock(&lloop_mutex);
661 case LL_IOC_LLOOP_DETACH: {
662 err = loop_clr_fd(lo, bdev, 2);
664 blkdev_put(bdev, 0); /* grabbed in LLOOP_ATTACH */
668 case LL_IOC_LLOOP_INFO: {
671 if (lo->lo_backing_file == NULL) {
676 inode = lo->lo_backing_file->f_dentry->d_inode;
677 if (lo->lo_state == LLOOP_BOUND)
678 fid = ll_i2info(inode)->lli_fid;
682 if (copy_to_user((struct lu_fid *)arg, &fid, sizeof(fid)))
691 mutex_unlock(&lloop_mutex);
696 static struct block_device_operations lo_fops = {
697 .owner = THIS_MODULE,
699 .release = lo_release,
703 /* dynamic iocontrol callback.
704 * This callback is registered in lloop_init and will be called by
707 * This is a llite regular file ioctl function. It takes the responsibility
708 * of attaching or detaching a file by a lloop's device numner.
710 static enum llioc_iter lloop_ioctl(struct inode *unused, struct file *file,
711 unsigned int cmd, unsigned long arg,
712 void *magic, int *rcp)
714 struct lloop_device *lo = NULL;
715 struct block_device *bdev = NULL;
719 if (magic != ll_iocontrol_magic)
723 GOTO(out1, err = -ENODEV);
725 CWARN("Enter llop_ioctl\n");
727 mutex_lock(&lloop_mutex);
729 case LL_IOC_LLOOP_ATTACH: {
730 struct lloop_device *lo_free = NULL;
733 for (i = 0; i < max_loop; i++, lo = NULL) {
735 if (lo->lo_state == LLOOP_UNBOUND) {
740 if (lo->lo_backing_file->f_dentry->d_inode ==
741 file->f_dentry->d_inode)
745 GOTO(out, err = -EBUSY);
748 dev = MKDEV(lloop_major, lo->lo_number);
750 /* quit if the used pointer is writable */
751 if (put_user((long)old_encode_dev(dev), (long*)arg))
752 GOTO(out, err = -EFAULT);
754 bdev = blkdev_get_by_dev(dev, file->f_mode, NULL);
756 GOTO(out, err = PTR_ERR(bdev));
759 err = loop_set_fd(lo, NULL, bdev, file);
768 case LL_IOC_LLOOP_DETACH_BYDEV: {
771 dev = old_decode_dev(arg);
772 if (MAJOR(dev) != lloop_major)
773 GOTO(out, err = -EINVAL);
776 if (minor > max_loop - 1)
777 GOTO(out, err = -EINVAL);
779 lo = &loop_dev[minor];
780 if (lo->lo_state != LLOOP_BOUND)
781 GOTO(out, err = -EINVAL);
783 bdev = lo->lo_device;
784 err = loop_clr_fd(lo, bdev, 1);
786 blkdev_put(bdev, 0); /* grabbed in LLOOP_ATTACH */
797 mutex_unlock(&lloop_mutex);
804 static int __init lloop_init(void)
807 unsigned int cmdlist[] = {
809 LL_IOC_LLOOP_DETACH_BYDEV,
812 if (max_loop < 1 || max_loop > 256) {
813 max_loop = MAX_LOOP_DEFAULT;
814 CWARN("lloop: invalid max_loop (must be between"
815 " 1 and 256), using default (%u)\n", max_loop);
818 lloop_major = register_blkdev(0, "lloop");
822 CDEBUG(D_CONFIG, "registered lloop major %d with %u minors\n",
823 lloop_major, max_loop);
825 ll_iocontrol_magic = ll_iocontrol_register(lloop_ioctl, 2, cmdlist);
826 if (ll_iocontrol_magic == NULL)
829 OBD_ALLOC_WAIT(loop_dev, max_loop * sizeof(*loop_dev));
833 OBD_ALLOC_WAIT(disks, max_loop * sizeof(*disks));
837 for (i = 0; i < max_loop; i++) {
838 disks[i] = alloc_disk(1);
843 mutex_init(&lloop_mutex);
845 for (i = 0; i < max_loop; i++) {
846 struct lloop_device *lo = &loop_dev[i];
847 struct gendisk *disk = disks[i];
849 lo->lo_queue = blk_alloc_queue(GFP_KERNEL);
853 mutex_init(&lo->lo_ctl_mutex);
854 sema_init(&lo->lo_sem, 0);
855 init_waitqueue_head(&lo->lo_bh_wait);
857 spin_lock_init(&lo->lo_lock);
858 disk->major = lloop_major;
859 disk->first_minor = i;
860 disk->fops = &lo_fops;
861 sprintf(disk->disk_name, "lloop%d", i);
862 disk->private_data = lo;
863 disk->queue = lo->lo_queue;
866 /* We cannot fail after we call this, so another loop!*/
867 for (i = 0; i < max_loop; i++)
873 blk_cleanup_queue(loop_dev[i].lo_queue);
878 OBD_FREE(disks, max_loop * sizeof(*disks));
880 OBD_FREE(loop_dev, max_loop * sizeof(*loop_dev));
882 unregister_blkdev(lloop_major, "lloop");
883 ll_iocontrol_unregister(ll_iocontrol_magic);
884 CERROR("lloop: ran out of memory\n");
888 static void lloop_exit(void)
892 ll_iocontrol_unregister(ll_iocontrol_magic);
893 for (i = 0; i < max_loop; i++) {
894 del_gendisk(disks[i]);
895 blk_cleanup_queue(loop_dev[i].lo_queue);
898 unregister_blkdev(lloop_major, "lloop");
900 OBD_FREE(disks, max_loop * sizeof(*disks));
901 OBD_FREE(loop_dev, max_loop * sizeof(*loop_dev));
904 module_init(lloop_init);
905 module_exit(lloop_exit);
907 CFS_MODULE_PARM(max_loop, "i", int, 0444, "maximum of lloop_device");
908 MODULE_AUTHOR("Sun Microsystems, Inc. <http://www.lustre.org/>");
909 MODULE_DESCRIPTION("Lustre virtual block device");
910 MODULE_LICENSE("GPL");