linux/drivers/virtio/virtio_ring.c
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   1/* Virtio ring implementation.
   2 *
   3 *  Copyright 2007 Rusty Russell IBM Corporation
   4 *
   5 *  This program is free software; you can redistribute it and/or modify
   6 *  it under the terms of the GNU General Public License as published by
   7 *  the Free Software Foundation; either version 2 of the License, or
   8 *  (at your option) any later version.
   9 *
  10 *  This program is distributed in the hope that it will be useful,
  11 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  12 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13 *  GNU General Public License for more details.
  14 *
  15 *  You should have received a copy of the GNU General Public License
  16 *  along with this program; if not, write to the Free Software
  17 *  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
  18 */
  19#include <linux/virtio.h>
  20#include <linux/virtio_ring.h>
  21#include <linux/virtio_config.h>
  22#include <linux/device.h>
  23#include <linux/slab.h>
  24#include <linux/module.h>
  25#include <linux/hrtimer.h>
  26
  27/* virtio guest is communicating with a virtual "device" that actually runs on
  28 * a host processor.  Memory barriers are used to control SMP effects. */
  29#ifdef CONFIG_SMP
  30/* Where possible, use SMP barriers which are more lightweight than mandatory
  31 * barriers, because mandatory barriers control MMIO effects on accesses
  32 * through relaxed memory I/O windows (which virtio-pci does not use). */
  33#define virtio_mb(vq) \
  34        do { if ((vq)->weak_barriers) smp_mb(); else mb(); } while(0)
  35#define virtio_rmb(vq) \
  36        do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
  37#define virtio_wmb(vq) \
  38        do { if ((vq)->weak_barriers) smp_wmb(); else wmb(); } while(0)
  39#else
  40/* We must force memory ordering even if guest is UP since host could be
  41 * running on another CPU, but SMP barriers are defined to barrier() in that
  42 * configuration. So fall back to mandatory barriers instead. */
  43#define virtio_mb(vq) mb()
  44#define virtio_rmb(vq) rmb()
  45#define virtio_wmb(vq) wmb()
  46#endif
  47
  48#ifdef DEBUG
  49/* For development, we want to crash whenever the ring is screwed. */
  50#define BAD_RING(_vq, fmt, args...)                             \
  51        do {                                                    \
  52                dev_err(&(_vq)->vq.vdev->dev,                   \
  53                        "%s:"fmt, (_vq)->vq.name, ##args);      \
  54                BUG();                                          \
  55        } while (0)
  56/* Caller is supposed to guarantee no reentry. */
  57#define START_USE(_vq)                                          \
  58        do {                                                    \
  59                if ((_vq)->in_use)                              \
  60                        panic("%s:in_use = %i\n",               \
  61                              (_vq)->vq.name, (_vq)->in_use);   \
  62                (_vq)->in_use = __LINE__;                       \
  63        } while (0)
  64#define END_USE(_vq) \
  65        do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
  66#else
  67#define BAD_RING(_vq, fmt, args...)                             \
  68        do {                                                    \
  69                dev_err(&_vq->vq.vdev->dev,                     \
  70                        "%s:"fmt, (_vq)->vq.name, ##args);      \
  71                (_vq)->broken = true;                           \
  72        } while (0)
  73#define START_USE(vq)
  74#define END_USE(vq)
  75#endif
  76
  77struct vring_virtqueue
  78{
  79        struct virtqueue vq;
  80
  81        /* Actual memory layout for this queue */
  82        struct vring vring;
  83
  84        /* Can we use weak barriers? */
  85        bool weak_barriers;
  86
  87        /* Other side has made a mess, don't try any more. */
  88        bool broken;
  89
  90        /* Host supports indirect buffers */
  91        bool indirect;
  92
  93        /* Host publishes avail event idx */
  94        bool event;
  95
  96        /* Number of free buffers */
  97        unsigned int num_free;
  98        /* Head of free buffer list. */
  99        unsigned int free_head;
 100        /* Number we've added since last sync. */
 101        unsigned int num_added;
 102
 103        /* Last used index we've seen. */
 104        u16 last_used_idx;
 105
 106        /* How to notify other side. FIXME: commonalize hcalls! */
 107        void (*notify)(struct virtqueue *vq);
 108
 109#ifdef DEBUG
 110        /* They're supposed to lock for us. */
 111        unsigned int in_use;
 112
 113        /* Figure out if their kicks are too delayed. */
 114        bool last_add_time_valid;
 115        ktime_t last_add_time;
 116#endif
 117
 118        /* Tokens for callbacks. */
 119        void *data[];
 120};
 121
 122#define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 123
 124/* Set up an indirect table of descriptors and add it to the queue. */
 125static int vring_add_indirect(struct vring_virtqueue *vq,
 126                              struct scatterlist sg[],
 127                              unsigned int out,
 128                              unsigned int in,
 129                              gfp_t gfp)
 130{
 131        struct vring_desc *desc;
 132        unsigned head;
 133        int i;
 134
 135        desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
 136        if (!desc)
 137                return -ENOMEM;
 138
 139        /* Transfer entries from the sg list into the indirect page */
 140        for (i = 0; i < out; i++) {
 141                desc[i].flags = VRING_DESC_F_NEXT;
 142                desc[i].addr = sg_phys(sg);
 143                desc[i].len = sg->length;
 144                desc[i].next = i+1;
 145                sg++;
 146        }
 147        for (; i < (out + in); i++) {
 148                desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 149                desc[i].addr = sg_phys(sg);
 150                desc[i].len = sg->length;
 151                desc[i].next = i+1;
 152                sg++;
 153        }
 154
 155        /* Last one doesn't continue. */
 156        desc[i-1].flags &= ~VRING_DESC_F_NEXT;
 157        desc[i-1].next = 0;
 158
 159        /* We're about to use a buffer */
 160        vq->num_free--;
 161
 162        /* Use a single buffer which doesn't continue */
 163        head = vq->free_head;
 164        vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
 165        vq->vring.desc[head].addr = virt_to_phys(desc);
 166        vq->vring.desc[head].len = i * sizeof(struct vring_desc);
 167
 168        /* Update free pointer */
 169        vq->free_head = vq->vring.desc[head].next;
 170
 171        return head;
 172}
 173
 174/**
 175 * virtqueue_add_buf - expose buffer to other end
 176 * @vq: the struct virtqueue we're talking about.
 177 * @sg: the description of the buffer(s).
 178 * @out_num: the number of sg readable by other side
 179 * @in_num: the number of sg which are writable (after readable ones)
 180 * @data: the token identifying the buffer.
 181 * @gfp: how to do memory allocations (if necessary).
 182 *
 183 * Caller must ensure we don't call this with other virtqueue operations
 184 * at the same time (except where noted).
 185 *
 186 * Returns remaining capacity of queue or a negative error
 187 * (ie. ENOSPC).  Note that it only really makes sense to treat all
 188 * positive return values as "available": indirect buffers mean that
 189 * we can put an entire sg[] array inside a single queue entry.
 190 */
 191int virtqueue_add_buf(struct virtqueue *_vq,
 192                      struct scatterlist sg[],
 193                      unsigned int out,
 194                      unsigned int in,
 195                      void *data,
 196                      gfp_t gfp)
 197{
 198        struct vring_virtqueue *vq = to_vvq(_vq);
 199        unsigned int i, avail, uninitialized_var(prev);
 200        int head;
 201
 202        START_USE(vq);
 203
 204        BUG_ON(data == NULL);
 205
 206#ifdef DEBUG
 207        {
 208                ktime_t now = ktime_get();
 209
 210                /* No kick or get, with .1 second between?  Warn. */
 211                if (vq->last_add_time_valid)
 212                        WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
 213                                            > 100);
 214                vq->last_add_time = now;
 215                vq->last_add_time_valid = true;
 216        }
 217#endif
 218
 219        /* If the host supports indirect descriptor tables, and we have multiple
 220         * buffers, then go indirect. FIXME: tune this threshold */
 221        if (vq->indirect && (out + in) > 1 && vq->num_free) {
 222                head = vring_add_indirect(vq, sg, out, in, gfp);
 223                if (likely(head >= 0))
 224                        goto add_head;
 225        }
 226
 227        BUG_ON(out + in > vq->vring.num);
 228        BUG_ON(out + in == 0);
 229
 230        if (vq->num_free < out + in) {
 231                pr_debug("Can't add buf len %i - avail = %i\n",
 232                         out + in, vq->num_free);
 233                /* FIXME: for historical reasons, we force a notify here if
 234                 * there are outgoing parts to the buffer.  Presumably the
 235                 * host should service the ring ASAP. */
 236                if (out)
 237                        vq->notify(&vq->vq);
 238                END_USE(vq);
 239                return -ENOSPC;
 240        }
 241
 242        /* We're about to use some buffers from the free list. */
 243        vq->num_free -= out + in;
 244
 245        head = vq->free_head;
 246        for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
 247                vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
 248                vq->vring.desc[i].addr = sg_phys(sg);
 249                vq->vring.desc[i].len = sg->length;
 250                prev = i;
 251                sg++;
 252        }
 253        for (; in; i = vq->vring.desc[i].next, in--) {
 254                vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 255                vq->vring.desc[i].addr = sg_phys(sg);
 256                vq->vring.desc[i].len = sg->length;
 257                prev = i;
 258                sg++;
 259        }
 260        /* Last one doesn't continue. */
 261        vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
 262
 263        /* Update free pointer */
 264        vq->free_head = i;
 265
 266add_head:
 267        /* Set token. */
 268        vq->data[head] = data;
 269
 270        /* Put entry in available array (but don't update avail->idx until they
 271         * do sync). */
 272        avail = (vq->vring.avail->idx & (vq->vring.num-1));
 273        vq->vring.avail->ring[avail] = head;
 274
 275        /* Descriptors and available array need to be set before we expose the
 276         * new available array entries. */
 277        virtio_wmb(vq);
 278        vq->vring.avail->idx++;
 279        vq->num_added++;
 280
 281        /* This is very unlikely, but theoretically possible.  Kick
 282         * just in case. */
 283        if (unlikely(vq->num_added == (1 << 16) - 1))
 284                virtqueue_kick(_vq);
 285
 286        pr_debug("Added buffer head %i to %p\n", head, vq);
 287        END_USE(vq);
 288
 289        return vq->num_free;
 290}
 291EXPORT_SYMBOL_GPL(virtqueue_add_buf);
 292
 293/**
 294 * virtqueue_kick_prepare - first half of split virtqueue_kick call.
 295 * @vq: the struct virtqueue
 296 *
 297 * Instead of virtqueue_kick(), you can do:
 298 *      if (virtqueue_kick_prepare(vq))
 299 *              virtqueue_notify(vq);
 300 *
 301 * This is sometimes useful because the virtqueue_kick_prepare() needs
 302 * to be serialized, but the actual virtqueue_notify() call does not.
 303 */
 304bool virtqueue_kick_prepare(struct virtqueue *_vq)
 305{
 306        struct vring_virtqueue *vq = to_vvq(_vq);
 307        u16 new, old;
 308        bool needs_kick;
 309
 310        START_USE(vq);
 311        /* We need to expose available array entries before checking avail
 312         * event. */
 313        virtio_mb(vq);
 314
 315        old = vq->vring.avail->idx - vq->num_added;
 316        new = vq->vring.avail->idx;
 317        vq->num_added = 0;
 318
 319#ifdef DEBUG
 320        if (vq->last_add_time_valid) {
 321                WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
 322                                              vq->last_add_time)) > 100);
 323        }
 324        vq->last_add_time_valid = false;
 325#endif
 326
 327        if (vq->event) {
 328                needs_kick = vring_need_event(vring_avail_event(&vq->vring),
 329                                              new, old);
 330        } else {
 331                needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
 332        }
 333        END_USE(vq);
 334        return needs_kick;
 335}
 336EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
 337
 338/**
 339 * virtqueue_notify - second half of split virtqueue_kick call.
 340 * @vq: the struct virtqueue
 341 *
 342 * This does not need to be serialized.
 343 */
 344void virtqueue_notify(struct virtqueue *_vq)
 345{
 346        struct vring_virtqueue *vq = to_vvq(_vq);
 347
 348        /* Prod other side to tell it about changes. */
 349        vq->notify(_vq);
 350}
 351EXPORT_SYMBOL_GPL(virtqueue_notify);
 352
 353/**
 354 * virtqueue_kick - update after add_buf
 355 * @vq: the struct virtqueue
 356 *
 357 * After one or more virtqueue_add_buf calls, invoke this to kick
 358 * the other side.
 359 *
 360 * Caller must ensure we don't call this with other virtqueue
 361 * operations at the same time (except where noted).
 362 */
 363void virtqueue_kick(struct virtqueue *vq)
 364{
 365        if (virtqueue_kick_prepare(vq))
 366                virtqueue_notify(vq);
 367}
 368EXPORT_SYMBOL_GPL(virtqueue_kick);
 369
 370static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
 371{
 372        unsigned int i;
 373
 374        /* Clear data ptr. */
 375        vq->data[head] = NULL;
 376
 377        /* Put back on free list: find end */
 378        i = head;
 379
 380        /* Free the indirect table */
 381        if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
 382                kfree(phys_to_virt(vq->vring.desc[i].addr));
 383
 384        while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
 385                i = vq->vring.desc[i].next;
 386                vq->num_free++;
 387        }
 388
 389        vq->vring.desc[i].next = vq->free_head;
 390        vq->free_head = head;
 391        /* Plus final descriptor */
 392        vq->num_free++;
 393}
 394
 395static inline bool more_used(const struct vring_virtqueue *vq)
 396{
 397        return vq->last_used_idx != vq->vring.used->idx;
 398}
 399
 400/**
 401 * virtqueue_get_buf - get the next used buffer
 402 * @vq: the struct virtqueue we're talking about.
 403 * @len: the length written into the buffer
 404 *
 405 * If the driver wrote data into the buffer, @len will be set to the
 406 * amount written.  This means you don't need to clear the buffer
 407 * beforehand to ensure there's no data leakage in the case of short
 408 * writes.
 409 *
 410 * Caller must ensure we don't call this with other virtqueue
 411 * operations at the same time (except where noted).
 412 *
 413 * Returns NULL if there are no used buffers, or the "data" token
 414 * handed to virtqueue_add_buf().
 415 */
 416void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 417{
 418        struct vring_virtqueue *vq = to_vvq(_vq);
 419        void *ret;
 420        unsigned int i;
 421        u16 last_used;
 422
 423        START_USE(vq);
 424
 425        if (unlikely(vq->broken)) {
 426                END_USE(vq);
 427                return NULL;
 428        }
 429
 430        if (!more_used(vq)) {
 431                pr_debug("No more buffers in queue\n");
 432                END_USE(vq);
 433                return NULL;
 434        }
 435
 436        /* Only get used array entries after they have been exposed by host. */
 437        virtio_rmb(vq);
 438
 439        last_used = (vq->last_used_idx & (vq->vring.num - 1));
 440        i = vq->vring.used->ring[last_used].id;
 441        *len = vq->vring.used->ring[last_used].len;
 442
 443        if (unlikely(i >= vq->vring.num)) {
 444                BAD_RING(vq, "id %u out of range\n", i);
 445                return NULL;
 446        }
 447        if (unlikely(!vq->data[i])) {
 448                BAD_RING(vq, "id %u is not a head!\n", i);
 449                return NULL;
 450        }
 451
 452        /* detach_buf clears data, so grab it now. */
 453        ret = vq->data[i];
 454        detach_buf(vq, i);
 455        vq->last_used_idx++;
 456        /* If we expect an interrupt for the next entry, tell host
 457         * by writing event index and flush out the write before
 458         * the read in the next get_buf call. */
 459        if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
 460                vring_used_event(&vq->vring) = vq->last_used_idx;
 461                virtio_mb(vq);
 462        }
 463
 464#ifdef DEBUG
 465        vq->last_add_time_valid = false;
 466#endif
 467
 468        END_USE(vq);
 469        return ret;
 470}
 471EXPORT_SYMBOL_GPL(virtqueue_get_buf);
 472
 473/**
 474 * virtqueue_disable_cb - disable callbacks
 475 * @vq: the struct virtqueue we're talking about.
 476 *
 477 * Note that this is not necessarily synchronous, hence unreliable and only
 478 * useful as an optimization.
 479 *
 480 * Unlike other operations, this need not be serialized.
 481 */
 482void virtqueue_disable_cb(struct virtqueue *_vq)
 483{
 484        struct vring_virtqueue *vq = to_vvq(_vq);
 485
 486        vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 487}
 488EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
 489
 490/**
 491 * virtqueue_enable_cb - restart callbacks after disable_cb.
 492 * @vq: the struct virtqueue we're talking about.
 493 *
 494 * This re-enables callbacks; it returns "false" if there are pending
 495 * buffers in the queue, to detect a possible race between the driver
 496 * checking for more work, and enabling callbacks.
 497 *
 498 * Caller must ensure we don't call this with other virtqueue
 499 * operations at the same time (except where noted).
 500 */
 501bool virtqueue_enable_cb(struct virtqueue *_vq)
 502{
 503        struct vring_virtqueue *vq = to_vvq(_vq);
 504
 505        START_USE(vq);
 506
 507        /* We optimistically turn back on interrupts, then check if there was
 508         * more to do. */
 509        /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
 510         * either clear the flags bit or point the event index at the next
 511         * entry. Always do both to keep code simple. */
 512        vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 513        vring_used_event(&vq->vring) = vq->last_used_idx;
 514        virtio_mb(vq);
 515        if (unlikely(more_used(vq))) {
 516                END_USE(vq);
 517                return false;
 518        }
 519
 520        END_USE(vq);
 521        return true;
 522}
 523EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
 524
 525/**
 526 * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
 527 * @vq: the struct virtqueue we're talking about.
 528 *
 529 * This re-enables callbacks but hints to the other side to delay
 530 * interrupts until most of the available buffers have been processed;
 531 * it returns "false" if there are many pending buffers in the queue,
 532 * to detect a possible race between the driver checking for more work,
 533 * and enabling callbacks.
 534 *
 535 * Caller must ensure we don't call this with other virtqueue
 536 * operations at the same time (except where noted).
 537 */
 538bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 539{
 540        struct vring_virtqueue *vq = to_vvq(_vq);
 541        u16 bufs;
 542
 543        START_USE(vq);
 544
 545        /* We optimistically turn back on interrupts, then check if there was
 546         * more to do. */
 547        /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
 548         * either clear the flags bit or point the event index at the next
 549         * entry. Always do both to keep code simple. */
 550        vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 551        /* TODO: tune this threshold */
 552        bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
 553        vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
 554        virtio_mb(vq);
 555        if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
 556                END_USE(vq);
 557                return false;
 558        }
 559
 560        END_USE(vq);
 561        return true;
 562}
 563EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
 564
 565/**
 566 * virtqueue_detach_unused_buf - detach first unused buffer
 567 * @vq: the struct virtqueue we're talking about.
 568 *
 569 * Returns NULL or the "data" token handed to virtqueue_add_buf().
 570 * This is not valid on an active queue; it is useful only for device
 571 * shutdown.
 572 */
 573void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
 574{
 575        struct vring_virtqueue *vq = to_vvq(_vq);
 576        unsigned int i;
 577        void *buf;
 578
 579        START_USE(vq);
 580
 581        for (i = 0; i < vq->vring.num; i++) {
 582                if (!vq->data[i])
 583                        continue;
 584                /* detach_buf clears data, so grab it now. */
 585                buf = vq->data[i];
 586                detach_buf(vq, i);
 587                vq->vring.avail->idx--;
 588                END_USE(vq);
 589                return buf;
 590        }
 591        /* That should have freed everything. */
 592        BUG_ON(vq->num_free != vq->vring.num);
 593
 594        END_USE(vq);
 595        return NULL;
 596}
 597EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
 598
 599irqreturn_t vring_interrupt(int irq, void *_vq)
 600{
 601        struct vring_virtqueue *vq = to_vvq(_vq);
 602
 603        if (!more_used(vq)) {
 604                pr_debug("virtqueue interrupt with no work for %p\n", vq);
 605                return IRQ_NONE;
 606        }
 607
 608        if (unlikely(vq->broken))
 609                return IRQ_HANDLED;
 610
 611        pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
 612        if (vq->vq.callback)
 613                vq->vq.callback(&vq->vq);
 614
 615        return IRQ_HANDLED;
 616}
 617EXPORT_SYMBOL_GPL(vring_interrupt);
 618
 619struct virtqueue *vring_new_virtqueue(unsigned int num,
 620                                      unsigned int vring_align,
 621                                      struct virtio_device *vdev,
 622                                      bool weak_barriers,
 623                                      void *pages,
 624                                      void (*notify)(struct virtqueue *),
 625                                      void (*callback)(struct virtqueue *),
 626                                      const char *name)
 627{
 628        struct vring_virtqueue *vq;
 629        unsigned int i;
 630
 631        /* We assume num is a power of 2. */
 632        if (num & (num - 1)) {
 633                dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
 634                return NULL;
 635        }
 636
 637        vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
 638        if (!vq)
 639                return NULL;
 640
 641        vring_init(&vq->vring, num, pages, vring_align);
 642        vq->vq.callback = callback;
 643        vq->vq.vdev = vdev;
 644        vq->vq.name = name;
 645        vq->notify = notify;
 646        vq->weak_barriers = weak_barriers;
 647        vq->broken = false;
 648        vq->last_used_idx = 0;
 649        vq->num_added = 0;
 650        list_add_tail(&vq->vq.list, &vdev->vqs);
 651#ifdef DEBUG
 652        vq->in_use = false;
 653        vq->last_add_time_valid = false;
 654#endif
 655
 656        vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
 657        vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 658
 659        /* No callback?  Tell other side not to bother us. */
 660        if (!callback)
 661                vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 662
 663        /* Put everything in free lists. */
 664        vq->num_free = num;
 665        vq->free_head = 0;
 666        for (i = 0; i < num-1; i++) {
 667                vq->vring.desc[i].next = i+1;
 668                vq->data[i] = NULL;
 669        }
 670        vq->data[i] = NULL;
 671
 672        return &vq->vq;
 673}
 674EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 675
 676void vring_del_virtqueue(struct virtqueue *vq)
 677{
 678        list_del(&vq->list);
 679        kfree(to_vvq(vq));
 680}
 681EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 682
 683/* Manipulates transport-specific feature bits. */
 684void vring_transport_features(struct virtio_device *vdev)
 685{
 686        unsigned int i;
 687
 688        for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
 689                switch (i) {
 690                case VIRTIO_RING_F_INDIRECT_DESC:
 691                        break;
 692                case VIRTIO_RING_F_EVENT_IDX:
 693                        break;
 694                default:
 695                        /* We don't understand this bit. */
 696                        clear_bit(i, vdev->features);
 697                }
 698        }
 699}
 700EXPORT_SYMBOL_GPL(vring_transport_features);
 701
 702/**
 703 * virtqueue_get_vring_size - return the size of the virtqueue's vring
 704 * @vq: the struct virtqueue containing the vring of interest.
 705 *
 706 * Returns the size of the vring.  This is mainly used for boasting to
 707 * userspace.  Unlike other operations, this need not be serialized.
 708 */
 709unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
 710{
 711
 712        struct vring_virtqueue *vq = to_vvq(_vq);
 713
 714        return vq->vring.num;
 715}
 716EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);
 717
 718MODULE_LICENSE("GPL");
 719
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