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TOMOYO Linux Cross Reference
Linux/net/9p/trans_virtio.c

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  1 /*
  2  * The Virtio 9p transport driver
  3  *
  4  * This is a block based transport driver based on the lguest block driver
  5  * code.
  6  *
  7  *  Copyright (C) 2007, 2008 Eric Van Hensbergen, IBM Corporation
  8  *
  9  *  Based on virtio console driver
 10  *  Copyright (C) 2006, 2007 Rusty Russell, IBM Corporation
 11  *
 12  *  This program is free software; you can redistribute it and/or modify
 13  *  it under the terms of the GNU General Public License version 2
 14  *  as published by the Free Software Foundation.
 15  *
 16  *  This program is distributed in the hope that it will be useful,
 17  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 18  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 19  *  GNU General Public License for more details.
 20  *
 21  *  You should have received a copy of the GNU General Public License
 22  *  along with this program; if not, write to:
 23  *  Free Software Foundation
 24  *  51 Franklin Street, Fifth Floor
 25  *  Boston, MA  02111-1301  USA
 26  *
 27  */
 28 
 29 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 30 
 31 #include <linux/in.h>
 32 #include <linux/module.h>
 33 #include <linux/net.h>
 34 #include <linux/ipv6.h>
 35 #include <linux/errno.h>
 36 #include <linux/kernel.h>
 37 #include <linux/un.h>
 38 #include <linux/uaccess.h>
 39 #include <linux/inet.h>
 40 #include <linux/idr.h>
 41 #include <linux/file.h>
 42 #include <linux/highmem.h>
 43 #include <linux/slab.h>
 44 #include <net/9p/9p.h>
 45 #include <linux/parser.h>
 46 #include <net/9p/client.h>
 47 #include <net/9p/transport.h>
 48 #include <linux/scatterlist.h>
 49 #include <linux/swap.h>
 50 #include <linux/virtio.h>
 51 #include <linux/virtio_9p.h>
 52 #include "trans_common.h"
 53 
 54 #define VIRTQUEUE_NUM   128
 55 
 56 /* a single mutex to manage channel initialization and attachment */
 57 static DEFINE_MUTEX(virtio_9p_lock);
 58 static DECLARE_WAIT_QUEUE_HEAD(vp_wq);
 59 static atomic_t vp_pinned = ATOMIC_INIT(0);
 60 
 61 /**
 62  * struct virtio_chan - per-instance transport information
 63  * @initialized: whether the channel is initialized
 64  * @inuse: whether the channel is in use
 65  * @lock: protects multiple elements within this structure
 66  * @client: client instance
 67  * @vdev: virtio dev associated with this channel
 68  * @vq: virtio queue associated with this channel
 69  * @sg: scatter gather list which is used to pack a request (protected?)
 70  *
 71  * We keep all per-channel information in a structure.
 72  * This structure is allocated within the devices dev->mem space.
 73  * A pointer to the structure will get put in the transport private.
 74  *
 75  */
 76 
 77 struct virtio_chan {
 78         bool inuse;
 79 
 80         spinlock_t lock;
 81 
 82         struct p9_client *client;
 83         struct virtio_device *vdev;
 84         struct virtqueue *vq;
 85         int ring_bufs_avail;
 86         wait_queue_head_t *vc_wq;
 87         /* This is global limit. Since we don't have a global structure,
 88          * will be placing it in each channel.
 89          */
 90         unsigned long p9_max_pages;
 91         /* Scatterlist: can be too big for stack. */
 92         struct scatterlist sg[VIRTQUEUE_NUM];
 93 
 94         int tag_len;
 95         /*
 96          * tag name to identify a mount Non-null terminated
 97          */
 98         char *tag;
 99 
100         struct list_head chan_list;
101 };
102 
103 static struct list_head virtio_chan_list;
104 
105 /* How many bytes left in this page. */
106 static unsigned int rest_of_page(void *data)
107 {
108         return PAGE_SIZE - ((unsigned long)data % PAGE_SIZE);
109 }
110 
111 /**
112  * p9_virtio_close - reclaim resources of a channel
113  * @client: client instance
114  *
115  * This reclaims a channel by freeing its resources and
116  * reseting its inuse flag.
117  *
118  */
119 
120 static void p9_virtio_close(struct p9_client *client)
121 {
122         struct virtio_chan *chan = client->trans;
123 
124         mutex_lock(&virtio_9p_lock);
125         if (chan)
126                 chan->inuse = false;
127         mutex_unlock(&virtio_9p_lock);
128 }
129 
130 /**
131  * req_done - callback which signals activity from the server
132  * @vq: virtio queue activity was received on
133  *
134  * This notifies us that the server has triggered some activity
135  * on the virtio channel - most likely a response to request we
136  * sent.  Figure out which requests now have responses and wake up
137  * those threads.
138  *
139  * Bugs: could do with some additional sanity checking, but appears to work.
140  *
141  */
142 
143 static void req_done(struct virtqueue *vq)
144 {
145         struct virtio_chan *chan = vq->vdev->priv;
146         struct p9_fcall *rc;
147         unsigned int len;
148         struct p9_req_t *req;
149         unsigned long flags;
150 
151         p9_debug(P9_DEBUG_TRANS, ": request done\n");
152 
153         while (1) {
154                 spin_lock_irqsave(&chan->lock, flags);
155                 rc = virtqueue_get_buf(chan->vq, &len);
156                 if (rc == NULL) {
157                         spin_unlock_irqrestore(&chan->lock, flags);
158                         break;
159                 }
160                 chan->ring_bufs_avail = 1;
161                 spin_unlock_irqrestore(&chan->lock, flags);
162                 /* Wakeup if anyone waiting for VirtIO ring space. */
163                 wake_up(chan->vc_wq);
164                 p9_debug(P9_DEBUG_TRANS, ": rc %p\n", rc);
165                 p9_debug(P9_DEBUG_TRANS, ": lookup tag %d\n", rc->tag);
166                 req = p9_tag_lookup(chan->client, rc->tag);
167                 req->status = REQ_STATUS_RCVD;
168                 p9_client_cb(chan->client, req);
169         }
170 }
171 
172 /**
173  * pack_sg_list - pack a scatter gather list from a linear buffer
174  * @sg: scatter/gather list to pack into
175  * @start: which segment of the sg_list to start at
176  * @limit: maximum segment to pack data to
177  * @data: data to pack into scatter/gather list
178  * @count: amount of data to pack into the scatter/gather list
179  *
180  * sg_lists have multiple segments of various sizes.  This will pack
181  * arbitrary data into an existing scatter gather list, segmenting the
182  * data as necessary within constraints.
183  *
184  */
185 
186 static int pack_sg_list(struct scatterlist *sg, int start,
187                         int limit, char *data, int count)
188 {
189         int s;
190         int index = start;
191 
192         while (count) {
193                 s = rest_of_page(data);
194                 if (s > count)
195                         s = count;
196                 BUG_ON(index > limit);
197                 /* Make sure we don't terminate early. */
198                 sg_unmark_end(&sg[index]);
199                 sg_set_buf(&sg[index++], data, s);
200                 count -= s;
201                 data += s;
202         }
203         if (index-start)
204                 sg_mark_end(&sg[index - 1]);
205         return index-start;
206 }
207 
208 /* We don't currently allow canceling of virtio requests */
209 static int p9_virtio_cancel(struct p9_client *client, struct p9_req_t *req)
210 {
211         return 1;
212 }
213 
214 /**
215  * pack_sg_list_p - Just like pack_sg_list. Instead of taking a buffer,
216  * this takes a list of pages.
217  * @sg: scatter/gather list to pack into
218  * @start: which segment of the sg_list to start at
219  * @pdata: a list of pages to add into sg.
220  * @nr_pages: number of pages to pack into the scatter/gather list
221  * @data: data to pack into scatter/gather list
222  * @count: amount of data to pack into the scatter/gather list
223  */
224 static int
225 pack_sg_list_p(struct scatterlist *sg, int start, int limit,
226                struct page **pdata, int nr_pages, char *data, int count)
227 {
228         int i = 0, s;
229         int data_off;
230         int index = start;
231 
232         BUG_ON(nr_pages > (limit - start));
233         /*
234          * if the first page doesn't start at
235          * page boundary find the offset
236          */
237         data_off = offset_in_page(data);
238         while (nr_pages) {
239                 s = rest_of_page(data);
240                 if (s > count)
241                         s = count;
242                 /* Make sure we don't terminate early. */
243                 sg_unmark_end(&sg[index]);
244                 sg_set_page(&sg[index++], pdata[i++], s, data_off);
245                 data_off = 0;
246                 data += s;
247                 count -= s;
248                 nr_pages--;
249         }
250 
251         if (index-start)
252                 sg_mark_end(&sg[index - 1]);
253         return index - start;
254 }
255 
256 /**
257  * p9_virtio_request - issue a request
258  * @client: client instance issuing the request
259  * @req: request to be issued
260  *
261  */
262 
263 static int
264 p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
265 {
266         int err;
267         int in, out, out_sgs, in_sgs;
268         unsigned long flags;
269         struct virtio_chan *chan = client->trans;
270         struct scatterlist *sgs[2];
271 
272         p9_debug(P9_DEBUG_TRANS, "9p debug: virtio request\n");
273 
274         req->status = REQ_STATUS_SENT;
275 req_retry:
276         spin_lock_irqsave(&chan->lock, flags);
277 
278         out_sgs = in_sgs = 0;
279         /* Handle out VirtIO ring buffers */
280         out = pack_sg_list(chan->sg, 0,
281                            VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);
282         if (out)
283                 sgs[out_sgs++] = chan->sg;
284 
285         in = pack_sg_list(chan->sg, out,
286                           VIRTQUEUE_NUM, req->rc->sdata, req->rc->capacity);
287         if (in)
288                 sgs[out_sgs + in_sgs++] = chan->sg + out;
289 
290         err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req->tc,
291                                 GFP_ATOMIC);
292         if (err < 0) {
293                 if (err == -ENOSPC) {
294                         chan->ring_bufs_avail = 0;
295                         spin_unlock_irqrestore(&chan->lock, flags);
296                         err = wait_event_interruptible(*chan->vc_wq,
297                                                         chan->ring_bufs_avail);
298                         if (err  == -ERESTARTSYS)
299                                 return err;
300 
301                         p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
302                         goto req_retry;
303                 } else {
304                         spin_unlock_irqrestore(&chan->lock, flags);
305                         p9_debug(P9_DEBUG_TRANS,
306                                  "virtio rpc add_sgs returned failure\n");
307                         return -EIO;
308                 }
309         }
310         virtqueue_kick(chan->vq);
311         spin_unlock_irqrestore(&chan->lock, flags);
312 
313         p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
314         return 0;
315 }
316 
317 static int p9_get_mapped_pages(struct virtio_chan *chan,
318                                struct page **pages, char *data,
319                                int nr_pages, int write, int kern_buf)
320 {
321         int err;
322         if (!kern_buf) {
323                 /*
324                  * We allow only p9_max_pages pinned. We wait for the
325                  * Other zc request to finish here
326                  */
327                 if (atomic_read(&vp_pinned) >= chan->p9_max_pages) {
328                         err = wait_event_interruptible(vp_wq,
329                               (atomic_read(&vp_pinned) < chan->p9_max_pages));
330                         if (err == -ERESTARTSYS)
331                                 return err;
332                 }
333                 err = p9_payload_gup(data, &nr_pages, pages, write);
334                 if (err < 0)
335                         return err;
336                 atomic_add(nr_pages, &vp_pinned);
337         } else {
338                 /* kernel buffer, no need to pin pages */
339                 int s, index = 0;
340                 int count = nr_pages;
341                 while (nr_pages) {
342                         s = rest_of_page(data);
343                         if (is_vmalloc_addr(data))
344                                 pages[index++] = vmalloc_to_page(data);
345                         else
346                                 pages[index++] = kmap_to_page(data);
347                         data += s;
348                         nr_pages--;
349                 }
350                 nr_pages = count;
351         }
352         return nr_pages;
353 }
354 
355 /**
356  * p9_virtio_zc_request - issue a zero copy request
357  * @client: client instance issuing the request
358  * @req: request to be issued
359  * @uidata: user bffer that should be ued for zero copy read
360  * @uodata: user buffer that shoud be user for zero copy write
361  * @inlen: read buffer size
362  * @olen: write buffer size
363  * @hdrlen: reader header size, This is the size of response protocol data
364  *
365  */
366 static int
367 p9_virtio_zc_request(struct p9_client *client, struct p9_req_t *req,
368                      char *uidata, char *uodata, int inlen,
369                      int outlen, int in_hdr_len, int kern_buf)
370 {
371         int in, out, err, out_sgs, in_sgs;
372         unsigned long flags;
373         int in_nr_pages = 0, out_nr_pages = 0;
374         struct page **in_pages = NULL, **out_pages = NULL;
375         struct virtio_chan *chan = client->trans;
376         struct scatterlist *sgs[4];
377 
378         p9_debug(P9_DEBUG_TRANS, "virtio request\n");
379 
380         if (uodata) {
381                 out_nr_pages = p9_nr_pages(uodata, outlen);
382                 out_pages = kmalloc(sizeof(struct page *) * out_nr_pages,
383                                     GFP_NOFS);
384                 if (!out_pages) {
385                         err = -ENOMEM;
386                         goto err_out;
387                 }
388                 out_nr_pages = p9_get_mapped_pages(chan, out_pages, uodata,
389                                                    out_nr_pages, 0, kern_buf);
390                 if (out_nr_pages < 0) {
391                         err = out_nr_pages;
392                         kfree(out_pages);
393                         out_pages = NULL;
394                         goto err_out;
395                 }
396         }
397         if (uidata) {
398                 in_nr_pages = p9_nr_pages(uidata, inlen);
399                 in_pages = kmalloc(sizeof(struct page *) * in_nr_pages,
400                                    GFP_NOFS);
401                 if (!in_pages) {
402                         err = -ENOMEM;
403                         goto err_out;
404                 }
405                 in_nr_pages = p9_get_mapped_pages(chan, in_pages, uidata,
406                                                   in_nr_pages, 1, kern_buf);
407                 if (in_nr_pages < 0) {
408                         err = in_nr_pages;
409                         kfree(in_pages);
410                         in_pages = NULL;
411                         goto err_out;
412                 }
413         }
414         req->status = REQ_STATUS_SENT;
415 req_retry_pinned:
416         spin_lock_irqsave(&chan->lock, flags);
417 
418         out_sgs = in_sgs = 0;
419 
420         /* out data */
421         out = pack_sg_list(chan->sg, 0,
422                            VIRTQUEUE_NUM, req->tc->sdata, req->tc->size);
423 
424         if (out)
425                 sgs[out_sgs++] = chan->sg;
426 
427         if (out_pages) {
428                 sgs[out_sgs++] = chan->sg + out;
429                 out += pack_sg_list_p(chan->sg, out, VIRTQUEUE_NUM,
430                                       out_pages, out_nr_pages, uodata, outlen);
431         }
432                 
433         /*
434          * Take care of in data
435          * For example TREAD have 11.
436          * 11 is the read/write header = PDU Header(7) + IO Size (4).
437          * Arrange in such a way that server places header in the
438          * alloced memory and payload onto the user buffer.
439          */
440         in = pack_sg_list(chan->sg, out,
441                           VIRTQUEUE_NUM, req->rc->sdata, in_hdr_len);
442         if (in)
443                 sgs[out_sgs + in_sgs++] = chan->sg + out;
444 
445         if (in_pages) {
446                 sgs[out_sgs + in_sgs++] = chan->sg + out + in;
447                 in += pack_sg_list_p(chan->sg, out + in, VIRTQUEUE_NUM,
448                                      in_pages, in_nr_pages, uidata, inlen);
449         }
450 
451         BUG_ON(out_sgs + in_sgs > ARRAY_SIZE(sgs));
452         err = virtqueue_add_sgs(chan->vq, sgs, out_sgs, in_sgs, req->tc,
453                                 GFP_ATOMIC);
454         if (err < 0) {
455                 if (err == -ENOSPC) {
456                         chan->ring_bufs_avail = 0;
457                         spin_unlock_irqrestore(&chan->lock, flags);
458                         err = wait_event_interruptible(*chan->vc_wq,
459                                                        chan->ring_bufs_avail);
460                         if (err  == -ERESTARTSYS)
461                                 goto err_out;
462 
463                         p9_debug(P9_DEBUG_TRANS, "Retry virtio request\n");
464                         goto req_retry_pinned;
465                 } else {
466                         spin_unlock_irqrestore(&chan->lock, flags);
467                         p9_debug(P9_DEBUG_TRANS,
468                                  "virtio rpc add_sgs returned failure\n");
469                         err = -EIO;
470                         goto err_out;
471                 }
472         }
473         virtqueue_kick(chan->vq);
474         spin_unlock_irqrestore(&chan->lock, flags);
475         p9_debug(P9_DEBUG_TRANS, "virtio request kicked\n");
476         err = wait_event_interruptible(*req->wq,
477                                        req->status >= REQ_STATUS_RCVD);
478         /*
479          * Non kernel buffers are pinned, unpin them
480          */
481 err_out:
482         if (!kern_buf) {
483                 if (in_pages) {
484                         p9_release_pages(in_pages, in_nr_pages);
485                         atomic_sub(in_nr_pages, &vp_pinned);
486                 }
487                 if (out_pages) {
488                         p9_release_pages(out_pages, out_nr_pages);
489                         atomic_sub(out_nr_pages, &vp_pinned);
490                 }
491                 /* wakeup anybody waiting for slots to pin pages */
492                 wake_up(&vp_wq);
493         }
494         kfree(in_pages);
495         kfree(out_pages);
496         return err;
497 }
498 
499 static ssize_t p9_mount_tag_show(struct device *dev,
500                                 struct device_attribute *attr, char *buf)
501 {
502         struct virtio_chan *chan;
503         struct virtio_device *vdev;
504 
505         vdev = dev_to_virtio(dev);
506         chan = vdev->priv;
507 
508         return snprintf(buf, chan->tag_len + 1, "%s", chan->tag);
509 }
510 
511 static DEVICE_ATTR(mount_tag, 0444, p9_mount_tag_show, NULL);
512 
513 /**
514  * p9_virtio_probe - probe for existence of 9P virtio channels
515  * @vdev: virtio device to probe
516  *
517  * This probes for existing virtio channels.
518  *
519  */
520 
521 static int p9_virtio_probe(struct virtio_device *vdev)
522 {
523         __u16 tag_len;
524         char *tag;
525         int err;
526         struct virtio_chan *chan;
527 
528         chan = kmalloc(sizeof(struct virtio_chan), GFP_KERNEL);
529         if (!chan) {
530                 pr_err("Failed to allocate virtio 9P channel\n");
531                 err = -ENOMEM;
532                 goto fail;
533         }
534 
535         chan->vdev = vdev;
536 
537         /* We expect one virtqueue, for requests. */
538         chan->vq = virtio_find_single_vq(vdev, req_done, "requests");
539         if (IS_ERR(chan->vq)) {
540                 err = PTR_ERR(chan->vq);
541                 goto out_free_vq;
542         }
543         chan->vq->vdev->priv = chan;
544         spin_lock_init(&chan->lock);
545 
546         sg_init_table(chan->sg, VIRTQUEUE_NUM);
547 
548         chan->inuse = false;
549         if (virtio_has_feature(vdev, VIRTIO_9P_MOUNT_TAG)) {
550                 virtio_cread(vdev, struct virtio_9p_config, tag_len, &tag_len);
551         } else {
552                 err = -EINVAL;
553                 goto out_free_vq;
554         }
555         tag = kmalloc(tag_len, GFP_KERNEL);
556         if (!tag) {
557                 err = -ENOMEM;
558                 goto out_free_vq;
559         }
560 
561         virtio_cread_bytes(vdev, offsetof(struct virtio_9p_config, tag),
562                            tag, tag_len);
563         chan->tag = tag;
564         chan->tag_len = tag_len;
565         err = sysfs_create_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
566         if (err) {
567                 goto out_free_tag;
568         }
569         chan->vc_wq = kmalloc(sizeof(wait_queue_head_t), GFP_KERNEL);
570         if (!chan->vc_wq) {
571                 err = -ENOMEM;
572                 goto out_free_tag;
573         }
574         init_waitqueue_head(chan->vc_wq);
575         chan->ring_bufs_avail = 1;
576         /* Ceiling limit to avoid denial of service attacks */
577         chan->p9_max_pages = nr_free_buffer_pages()/4;
578 
579         mutex_lock(&virtio_9p_lock);
580         list_add_tail(&chan->chan_list, &virtio_chan_list);
581         mutex_unlock(&virtio_9p_lock);
582 
583         /* Let udev rules use the new mount_tag attribute. */
584         kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
585 
586         return 0;
587 
588 out_free_tag:
589         kfree(tag);
590 out_free_vq:
591         vdev->config->del_vqs(vdev);
592         kfree(chan);
593 fail:
594         return err;
595 }
596 
597 
598 /**
599  * p9_virtio_create - allocate a new virtio channel
600  * @client: client instance invoking this transport
601  * @devname: string identifying the channel to connect to (unused)
602  * @args: args passed from sys_mount() for per-transport options (unused)
603  *
604  * This sets up a transport channel for 9p communication.  Right now
605  * we only match the first available channel, but eventually we couldlook up
606  * alternate channels by matching devname versus a virtio_config entry.
607  * We use a simple reference count mechanism to ensure that only a single
608  * mount has a channel open at a time.
609  *
610  */
611 
612 static int
613 p9_virtio_create(struct p9_client *client, const char *devname, char *args)
614 {
615         struct virtio_chan *chan;
616         int ret = -ENOENT;
617         int found = 0;
618 
619         mutex_lock(&virtio_9p_lock);
620         list_for_each_entry(chan, &virtio_chan_list, chan_list) {
621                 if (!strncmp(devname, chan->tag, chan->tag_len) &&
622                     strlen(devname) == chan->tag_len) {
623                         if (!chan->inuse) {
624                                 chan->inuse = true;
625                                 found = 1;
626                                 break;
627                         }
628                         ret = -EBUSY;
629                 }
630         }
631         mutex_unlock(&virtio_9p_lock);
632 
633         if (!found) {
634                 pr_err("no channels available\n");
635                 return ret;
636         }
637 
638         client->trans = (void *)chan;
639         client->status = Connected;
640         chan->client = client;
641 
642         return 0;
643 }
644 
645 /**
646  * p9_virtio_remove - clean up resources associated with a virtio device
647  * @vdev: virtio device to remove
648  *
649  */
650 
651 static void p9_virtio_remove(struct virtio_device *vdev)
652 {
653         struct virtio_chan *chan = vdev->priv;
654 
655         if (chan->inuse)
656                 p9_virtio_close(chan->client);
657         vdev->config->del_vqs(vdev);
658 
659         mutex_lock(&virtio_9p_lock);
660         list_del(&chan->chan_list);
661         mutex_unlock(&virtio_9p_lock);
662         sysfs_remove_file(&(vdev->dev.kobj), &dev_attr_mount_tag.attr);
663         kobject_uevent(&(vdev->dev.kobj), KOBJ_CHANGE);
664         kfree(chan->tag);
665         kfree(chan->vc_wq);
666         kfree(chan);
667 
668 }
669 
670 static struct virtio_device_id id_table[] = {
671         { VIRTIO_ID_9P, VIRTIO_DEV_ANY_ID },
672         { 0 },
673 };
674 
675 static unsigned int features[] = {
676         VIRTIO_9P_MOUNT_TAG,
677 };
678 
679 /* The standard "struct lguest_driver": */
680 static struct virtio_driver p9_virtio_drv = {
681         .feature_table  = features,
682         .feature_table_size = ARRAY_SIZE(features),
683         .driver.name    = KBUILD_MODNAME,
684         .driver.owner   = THIS_MODULE,
685         .id_table       = id_table,
686         .probe          = p9_virtio_probe,
687         .remove         = p9_virtio_remove,
688 };
689 
690 static struct p9_trans_module p9_virtio_trans = {
691         .name = "virtio",
692         .create = p9_virtio_create,
693         .close = p9_virtio_close,
694         .request = p9_virtio_request,
695         .zc_request = p9_virtio_zc_request,
696         .cancel = p9_virtio_cancel,
697         /*
698          * We leave one entry for input and one entry for response
699          * headers. We also skip one more entry to accomodate, address
700          * that are not at page boundary, that can result in an extra
701          * page in zero copy.
702          */
703         .maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
704         .def = 1,
705         .owner = THIS_MODULE,
706 };
707 
708 /* The standard init function */
709 static int __init p9_virtio_init(void)
710 {
711         INIT_LIST_HEAD(&virtio_chan_list);
712 
713         v9fs_register_trans(&p9_virtio_trans);
714         return register_virtio_driver(&p9_virtio_drv);
715 }
716 
717 static void __exit p9_virtio_cleanup(void)
718 {
719         unregister_virtio_driver(&p9_virtio_drv);
720         v9fs_unregister_trans(&p9_virtio_trans);
721 }
722 
723 module_init(p9_virtio_init);
724 module_exit(p9_virtio_cleanup);
725 
726 MODULE_DEVICE_TABLE(virtio, id_table);
727 MODULE_AUTHOR("Eric Van Hensbergen <ericvh@gmail.com>");
728 MODULE_DESCRIPTION("Virtio 9p Transport");
729 MODULE_LICENSE("GPL");
730 

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