drivers/hv/ring_buffer.c

   1 /*
   2  *
   3  * Copyright (c) 2009, Microsoft Corporation.
   4  *
   5  * This program is free software; you can redistribute it and/or modify it
   6  * under the terms and conditions of the GNU General Public License,
   7  * version 2, as published by the Free Software Foundation.
   8  *
   9  * This program is distributed in the hope it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
  12  * more details.
  13  *
  14  * You should have received a copy of the GNU General Public License along with
  15  * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
  16  * Place - Suite 330, Boston, MA 02111-1307 USA.
  17  *
  18  * Authors:
  19  *   Haiyang Zhang <haiyangz@microsoft.com>
  20  *   Hank Janssen  <hjanssen@microsoft.com>
  21  *   K. Y. Srinivasan <kys@microsoft.com>
  22  *
  23  */
  24 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
  25
  26 #include <linux/kernel.h>
  27 #include <linux/mm.h>
  28 #include <linux/hyperv.h>
  29
  30 #include "hyperv_vmbus.h"
  31
  32 void hv_begin_read(struct hv_ring_buffer_info *rbi)
  33 {
  34         rbi->ring_buffer->interrupt_mask = 1;
  35         mb();
  36 }
  37
  38 u32 hv_end_read(struct hv_ring_buffer_info *rbi)
  39 {
  40         u32 read;
  41         u32 write;
  42
  43         rbi->ring_buffer->interrupt_mask = 0;
  44         mb();
  45
  46         /*
  47          * Now check to see if the ring buffer is still empty.
  48          * If it is not, we raced and we need to process new
  49          * incoming messages.
  50          */
  51         hv_get_ringbuffer_availbytes(rbi, &read, &write);
  52
  53         return read;
  54 }
  55
  56 /*
  57  * When we write to the ring buffer, check if the host needs to
  58  * be signaled. Here is the details of this protocol:
  59  *
  60  *      1. The host guarantees that while it is draining the
  61  *         ring buffer, it will set the interrupt_mask to
  62  *         indicate it does not need to be interrupted when
  63  *         new data is placed.
  64  *
  65  *      2. The host guarantees that it will completely drain
  66  *         the ring buffer before exiting the read loop. Further,
  67  *         once the ring buffer is empty, it will clear the
  68  *         interrupt_mask and re-check to see if new data has
  69  *         arrived.
  70  */
  71
  72 static bool hv_need_to_signal(u32 old_write, struct hv_ring_buffer_info *rbi)
  73 {
  74         mb();
  75         if (rbi->ring_buffer->interrupt_mask)
  76                 return false;
  77
  78         /*
  79          * This is the only case we need to signal when the
  80          * ring transitions from being empty to non-empty.
  81          */
  82         if (old_write == rbi->ring_buffer->read_index)
  83                 return true;
  84
  85         return false;
  86 }
  87
  88 /*
  89  * To optimize the flow management on the send-side,
  90  * when the sender is blocked because of lack of
  91  * sufficient space in the ring buffer, potential the
  92  * consumer of the ring buffer can signal the producer.
  93  * This is controlled by the following parameters:
  94  *
  95  * 1. pending_send_sz: This is the size in bytes that the
  96  *    producer is trying to send.
  97  * 2. The feature bit feat_pending_send_sz set to indicate if
  98  *    the consumer of the ring will signal when the ring
  99  *    state transitions from being full to a state where
 100  *    there is room for the producer to send the pending packet.
 101  */
 102
 103 static bool hv_need_to_signal_on_read(u32 old_rd,
 104                                          struct hv_ring_buffer_info *rbi)
 105 {
 106         u32 prev_write_sz;
 107         u32 cur_write_sz;
 108         u32 r_size;
 109         u32 write_loc = rbi->ring_buffer->write_index;
 110         u32 read_loc = rbi->ring_buffer->read_index;
 111         u32 pending_sz = rbi->ring_buffer->pending_send_sz;
 112
 113         /*
 114          * If the other end is not blocked on write don't bother.
 115          */
 116         if (pending_sz == 0)
 117                 return false;
 118
 119         r_size = rbi->ring_datasize;
 120         cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
 121                         read_loc - write_loc;
 122
 123         prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
 124                         old_rd - write_loc;
 125
 126
 127         if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
 128                 return true;
 129
 130         return false;
 131 }
 132
 133 /*
 134  * hv_get_next_write_location()
 135  *
 136  * Get the next write location for the specified ring buffer
 137  *
 138  */
 139 static inline u32
 140 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
 141 {
 142         u32 next = ring_info->ring_buffer->write_index;
 143
 144         return next;
 145 }
 146
 147 /*
 148  * hv_set_next_write_location()
 149  *
 150  * Set the next write location for the specified ring buffer
 151  *
 152  */
 153 static inline void
 154 hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
 155                      u32 next_write_location)
 156 {
 157         ring_info->ring_buffer->write_index = next_write_location;
 158 }
 159
 160 /*
 161  * hv_get_next_read_location()
 162  *
 163  * Get the next read location for the specified ring buffer
 164  */
 165 static inline u32
 166 hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
 167 {
 168         u32 next = ring_info->ring_buffer->read_index;
 169
 170         return next;
 171 }
 172
 173 /*
 174  * hv_get_next_readlocation_withoffset()
 175  *
 176  * Get the next read location + offset for the specified ring buffer.
 177  * This allows the caller to skip
 178  */
 179 static inline u32
 180 hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
 181                                  u32 offset)
 182 {
 183         u32 next = ring_info->ring_buffer->read_index;
 184
 185         next += offset;
 186         next %= ring_info->ring_datasize;
 187
 188         return next;
 189 }
 190
 191 /*
 192  *
 193  * hv_set_next_read_location()
 194  *
 195  * Set the next read location for the specified ring buffer
 196  *
 197  */
 198 static inline void
 199 hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
 200                     u32 next_read_location)
 201 {
 202         ring_info->ring_buffer->read_index = next_read_location;
 203 }
 204
 205
 206 /*
 207  *
 208  * hv_get_ring_buffer()
 209  *
 210  * Get the start of the ring buffer
 211  */
 212 static inline void *
 213 hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
 214 {
 215         return (void *)ring_info->ring_buffer->buffer;
 216 }
 217
 218
 219 /*
 220  *
 221  * hv_get_ring_buffersize()
 222  *
 223  * Get the size of the ring buffer
 224  */
 225 static inline u32
 226 hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
 227 {
 228         return ring_info->ring_datasize;
 229 }
 230
 231 /*
 232  *
 233  * hv_get_ring_bufferindices()
 234  *
 235  * Get the read and write indices as u64 of the specified ring buffer
 236  *
 237  */
 238 static inline u64
 239 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
 240 {
 241         return (u64)ring_info->ring_buffer->write_index << 32;
 242 }
 243
 244 /*
 245  *
 246  * hv_copyfrom_ringbuffer()
 247  *
 248  * Helper routine to copy to source from ring buffer.
 249  * Assume there is enough room. Handles wrap-around in src case only!!
 250  *
 251  */
 252 static u32 hv_copyfrom_ringbuffer(
 253         struct hv_ring_buffer_info      *ring_info,
 254         void                            *dest,
 255         u32                             destlen,
 256         u32                             start_read_offset)
 257 {
 258         void *ring_buffer = hv_get_ring_buffer(ring_info);
 259         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 260
 261         u32 frag_len;
 262
 263         /* wrap-around detected at the src */
 264         if (destlen > ring_buffer_size - start_read_offset) {
 265                 frag_len = ring_buffer_size - start_read_offset;
 266
 267                 memcpy(dest, ring_buffer + start_read_offset, frag_len);
 268                 memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
 269         } else
 270
 271                 memcpy(dest, ring_buffer + start_read_offset, destlen);
 272
 273
 274         start_read_offset += destlen;
 275         start_read_offset %= ring_buffer_size;
 276
 277         return start_read_offset;
 278 }
 279
 280
 281 /*
 282  *
 283  * hv_copyto_ringbuffer()
 284  *
 285  * Helper routine to copy from source to ring buffer.
 286  * Assume there is enough room. Handles wrap-around in dest case only!!
 287  *
 288  */
 289 static u32 hv_copyto_ringbuffer(
 290         struct hv_ring_buffer_info      *ring_info,
 291         u32                             start_write_offset,
 292         void                            *src,
 293         u32                             srclen)
 294 {
 295         void *ring_buffer = hv_get_ring_buffer(ring_info);
 296         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 297         u32 frag_len;
 298
 299         /* wrap-around detected! */
 300         if (srclen > ring_buffer_size - start_write_offset) {
 301                 frag_len = ring_buffer_size - start_write_offset;
 302                 memcpy(ring_buffer + start_write_offset, src, frag_len);
 303                 memcpy(ring_buffer, src + frag_len, srclen - frag_len);
 304         } else
 305                 memcpy(ring_buffer + start_write_offset, src, srclen);
 306
 307         start_write_offset += srclen;
 308         start_write_offset %= ring_buffer_size;
 309
 310         return start_write_offset;
 311 }
 312
 313 /*
 314  *
 315  * hv_ringbuffer_get_debuginfo()
 316  *
 317  * Get various debug metrics for the specified ring buffer
 318  *
 319  */
 320 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 321                             struct hv_ring_buffer_debug_info *debug_info)
 322 {
 323         u32 bytes_avail_towrite;
 324         u32 bytes_avail_toread;
 325
 326         if (ring_info->ring_buffer) {
 327                 hv_get_ringbuffer_availbytes(ring_info,
 328                                         &bytes_avail_toread,
 329                                         &bytes_avail_towrite);
 330
 331                 debug_info->bytes_avail_toread = bytes_avail_toread;
 332                 debug_info->bytes_avail_towrite = bytes_avail_towrite;
 333                 debug_info->current_read_index =
 334                         ring_info->ring_buffer->read_index;
 335                 debug_info->current_write_index =
 336                         ring_info->ring_buffer->write_index;
 337                 debug_info->current_interrupt_mask =
 338                         ring_info->ring_buffer->interrupt_mask;
 339         }
 340 }
 341
 342 /*
 343  *
 344  * hv_ringbuffer_init()
 345  *
 346  *Initialize the ring buffer
 347  *
 348  */
 349 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 350                    void *buffer, u32 buflen)
 351 {
 352         if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
 353                 return -EINVAL;
 354
 355         memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
 356
 357         ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
 358         ring_info->ring_buffer->read_index =
 359                 ring_info->ring_buffer->write_index = 0;
 360
 361         ring_info->ring_size = buflen;
 362         ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
 363
 364         spin_lock_init(&ring_info->ring_lock);
 365
 366         return 0;
 367 }
 368
 369 /*
 370  *
 371  * hv_ringbuffer_cleanup()
 372  *
 373  * Cleanup the ring buffer
 374  *
 375  */
 376 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 377 {
 378 }
 379
 380 /*
 381  *
 382  * hv_ringbuffer_write()
 383  *
 384  * Write to the ring buffer
 385  *
 386  */
 387 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 388                     struct scatterlist *sglist, u32 sgcount, bool *signal)
 389 {
 390         int i = 0;
 391         u32 bytes_avail_towrite;
 392         u32 bytes_avail_toread;
 393         u32 totalbytes_towrite = 0;
 394
 395         struct scatterlist *sg;
 396         u32 next_write_location;
 397         u32 old_write;
 398         u64 prev_indices = 0;
 399         unsigned long flags;
 400
 401         for_each_sg(sglist, sg, sgcount, i)
 402         {
 403                 totalbytes_towrite += sg->length;
 404         }
 405
 406         totalbytes_towrite += sizeof(u64);
 407
 408         spin_lock_irqsave(&outring_info->ring_lock, flags);
 409
 410         hv_get_ringbuffer_availbytes(outring_info,
 411                                 &bytes_avail_toread,
 412                                 &bytes_avail_towrite);
 413
 414
 415         /* If there is only room for the packet, assume it is full. */
 416         /* Otherwise, the next time around, we think the ring buffer */
 417         /* is empty since the read index == write index */
 418         if (bytes_avail_towrite <= totalbytes_towrite) {
 419                 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 420                 return -EAGAIN;
 421         }
 422
 423         /* Write to the ring buffer */
 424         next_write_location = hv_get_next_write_location(outring_info);
 425
 426         old_write = next_write_location;
 427
 428         for_each_sg(sglist, sg, sgcount, i)
 429         {
 430                 next_write_location = hv_copyto_ringbuffer(outring_info,
 431                                                      next_write_location,
 432                                                      sg_virt(sg),
 433                                                      sg->length);
 434         }
 435
 436         /* Set previous packet start */
 437         prev_indices = hv_get_ring_bufferindices(outring_info);
 438
 439         next_write_location = hv_copyto_ringbuffer(outring_info,
 440                                              next_write_location,
 441                                              &prev_indices,
 442                                              sizeof(u64));
 443
 444         /* Issue a full memory barrier before updating the write index */
 445         mb();
 446
 447         /* Now, update the write location */
 448         hv_set_next_write_location(outring_info, next_write_location);
 449
 450
 451         spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 452
 453         *signal = hv_need_to_signal(old_write, outring_info);
 454         return 0;
 455 }
 456
 457
 458 /*
 459  *
 460  * hv_ringbuffer_peek()
 461  *
 462  * Read without advancing the read index
 463  *
 464  */
 465 int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
 466                    void *Buffer, u32 buflen)
 467 {
 468         u32 bytes_avail_towrite;
 469         u32 bytes_avail_toread;
 470         u32 next_read_location = 0;
 471         unsigned long flags;
 472
 473         spin_lock_irqsave(&Inring_info->ring_lock, flags);
 474
 475         hv_get_ringbuffer_availbytes(Inring_info,
 476                                 &bytes_avail_toread,
 477                                 &bytes_avail_towrite);
 478
 479         /* Make sure there is something to read */
 480         if (bytes_avail_toread < buflen) {
 481
 482                 spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
 483
 484                 return -EAGAIN;
 485         }
 486
 487         /* Convert to byte offset */
 488         next_read_location = hv_get_next_read_location(Inring_info);
 489
 490         next_read_location = hv_copyfrom_ringbuffer(Inring_info,
 491                                                 Buffer,
 492                                                 buflen,
 493                                                 next_read_location);
 494
 495         spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
 496
 497         return 0;
 498 }
 499
 500
 501 /*
 502  *
 503  * hv_ringbuffer_read()
 504  *
 505  * Read and advance the read index
 506  *
 507  */
 508 int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 509                    u32 buflen, u32 offset, bool *signal)
 510 {
 511         u32 bytes_avail_towrite;
 512         u32 bytes_avail_toread;
 513         u32 next_read_location = 0;
 514         u64 prev_indices = 0;
 515         unsigned long flags;
 516         u32 old_read;
 517
 518         if (buflen <= 0)
 519                 return -EINVAL;
 520
 521         spin_lock_irqsave(&inring_info->ring_lock, flags);
 522
 523         hv_get_ringbuffer_availbytes(inring_info,
 524                                 &bytes_avail_toread,
 525                                 &bytes_avail_towrite);
 526
 527         old_read = bytes_avail_toread;
 528
 529         /* Make sure there is something to read */
 530         if (bytes_avail_toread < buflen) {
 531                 spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 532
 533                 return -EAGAIN;
 534         }
 535
 536         next_read_location =
 537                 hv_get_next_readlocation_withoffset(inring_info, offset);
 538
 539         next_read_location = hv_copyfrom_ringbuffer(inring_info,
 540                                                 buffer,
 541                                                 buflen,
 542                                                 next_read_location);
 543
 544         next_read_location = hv_copyfrom_ringbuffer(inring_info,
 545                                                 &prev_indices,
 546                                                 sizeof(u64),
 547                                                 next_read_location);
 548
 549         /* Make sure all reads are done before we update the read index since */
 550         /* the writer may start writing to the read area once the read index */
 551         /*is updated */
 552         mb();
 553
 554         /* Update the read index */
 555         hv_set_next_read_location(inring_info, next_read_location);
 556
 557         spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 558
 559         *signal = hv_need_to_signal_on_read(old_read, inring_info);
 560
 561         return 0;
 562 }