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         smp_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         smp_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         if (rbi->ring_buffer->interrupt_mask)
  75                 return false;
  76
  77         /*
  78          * This is the only case we need to signal when the
  79          * ring transitions from being empty to non-empty.
  80          */
  81         if (old_write == rbi->ring_buffer->read_index)
  82                 return true;
  83
  84         return false;
  85 }
  86
  87 /*
  88  * To optimize the flow management on the send-side,
  89  * when the sender is blocked because of lack of
  90  * sufficient space in the ring buffer, potential the
  91  * consumer of the ring buffer can signal the producer.
  92  * This is controlled by the following parameters:
  93  *
  94  * 1. pending_send_sz: This is the size in bytes that the
  95  *    producer is trying to send.
  96  * 2. The feature bit feat_pending_send_sz set to indicate if
  97  *    the consumer of the ring will signal when the ring
  98  *    state transitions from being full to a state where
  99  *    there is room for the producer to send the pending packet.
 100  */
 101
 102 static bool hv_need_to_signal_on_read(u32 old_rd,
 103                                          struct hv_ring_buffer_info *rbi)
 104 {
 105         u32 prev_write_sz;
 106         u32 cur_write_sz;
 107         u32 r_size;
 108         u32 write_loc = rbi->ring_buffer->write_index;
 109         u32 read_loc = rbi->ring_buffer->read_index;
 110         u32 pending_sz = rbi->ring_buffer->pending_send_sz;
 111
 112         /*
 113          * If the other end is not blocked on write don't bother.
 114          */
 115         if (pending_sz == 0)
 116                 return false;
 117
 118         r_size = rbi->ring_datasize;
 119         cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
 120                         read_loc - write_loc;
 121
 122         prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
 123                         old_rd - write_loc;
 124
 125
 126         if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
 127                 return true;
 128
 129         return false;
 130 }
 131
 132 /*
 133  * hv_get_next_write_location()
 134  *
 135  * Get the next write location for the specified ring buffer
 136  *
 137  */
 138 static inline u32
 139 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
 140 {
 141         u32 next = ring_info->ring_buffer->write_index;
 142
 143         return next;
 144 }
 145
 146 /*
 147  * hv_set_next_write_location()
 148  *
 149  * Set the next write location for the specified ring buffer
 150  *
 151  */
 152 static inline void
 153 hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
 154                      u32 next_write_location)
 155 {
 156         ring_info->ring_buffer->write_index = next_write_location;
 157 }
 158
 159 /*
 160  * hv_get_next_read_location()
 161  *
 162  * Get the next read location for the specified ring buffer
 163  */
 164 static inline u32
 165 hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
 166 {
 167         u32 next = ring_info->ring_buffer->read_index;
 168
 169         return next;
 170 }
 171
 172 /*
 173  * hv_get_next_readlocation_withoffset()
 174  *
 175  * Get the next read location + offset for the specified ring buffer.
 176  * This allows the caller to skip
 177  */
 178 static inline u32
 179 hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
 180                                  u32 offset)
 181 {
 182         u32 next = ring_info->ring_buffer->read_index;
 183
 184         next += offset;
 185         next %= ring_info->ring_datasize;
 186
 187         return next;
 188 }
 189
 190 /*
 191  *
 192  * hv_set_next_read_location()
 193  *
 194  * Set the next read location for the specified ring buffer
 195  *
 196  */
 197 static inline void
 198 hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
 199                     u32 next_read_location)
 200 {
 201         ring_info->ring_buffer->read_index = next_read_location;
 202 }
 203
 204
 205 /*
 206  *
 207  * hv_get_ring_buffer()
 208  *
 209  * Get the start of the ring buffer
 210  */
 211 static inline void *
 212 hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
 213 {
 214         return (void *)ring_info->ring_buffer->buffer;
 215 }
 216
 217
 218 /*
 219  *
 220  * hv_get_ring_buffersize()
 221  *
 222  * Get the size of the ring buffer
 223  */
 224 static inline u32
 225 hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
 226 {
 227         return ring_info->ring_datasize;
 228 }
 229
 230 /*
 231  *
 232  * hv_get_ring_bufferindices()
 233  *
 234  * Get the read and write indices as u64 of the specified ring buffer
 235  *
 236  */
 237 static inline u64
 238 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
 239 {
 240         return (u64)ring_info->ring_buffer->write_index << 32;
 241 }
 242
 243 /*
 244  *
 245  * hv_copyfrom_ringbuffer()
 246  *
 247  * Helper routine to copy to source from ring buffer.
 248  * Assume there is enough room. Handles wrap-around in src case only!!
 249  *
 250  */
 251 static u32 hv_copyfrom_ringbuffer(
 252         struct hv_ring_buffer_info      *ring_info,
 253         void                            *dest,
 254         u32                             destlen,
 255         u32                             start_read_offset)
 256 {
 257         void *ring_buffer = hv_get_ring_buffer(ring_info);
 258         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 259
 260         u32 frag_len;
 261
 262         /* wrap-around detected at the src */
 263         if (destlen > ring_buffer_size - start_read_offset) {
 264                 frag_len = ring_buffer_size - start_read_offset;
 265
 266                 memcpy(dest, ring_buffer + start_read_offset, frag_len);
 267                 memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
 268         } else
 269
 270                 memcpy(dest, ring_buffer + start_read_offset, destlen);
 271
 272
 273         start_read_offset += destlen;
 274         start_read_offset %= ring_buffer_size;
 275
 276         return start_read_offset;
 277 }
 278
 279
 280 /*
 281  *
 282  * hv_copyto_ringbuffer()
 283  *
 284  * Helper routine to copy from source to ring buffer.
 285  * Assume there is enough room. Handles wrap-around in dest case only!!
 286  *
 287  */
 288 static u32 hv_copyto_ringbuffer(
 289         struct hv_ring_buffer_info      *ring_info,
 290         u32                             start_write_offset,
 291         void                            *src,
 292         u32                             srclen)
 293 {
 294         void *ring_buffer = hv_get_ring_buffer(ring_info);
 295         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 296         u32 frag_len;
 297
 298         /* wrap-around detected! */
 299         if (srclen > ring_buffer_size - start_write_offset) {
 300                 frag_len = ring_buffer_size - start_write_offset;
 301                 memcpy(ring_buffer + start_write_offset, src, frag_len);
 302                 memcpy(ring_buffer, src + frag_len, srclen - frag_len);
 303         } else
 304                 memcpy(ring_buffer + start_write_offset, src, srclen);
 305
 306         start_write_offset += srclen;
 307         start_write_offset %= ring_buffer_size;
 308
 309         return start_write_offset;
 310 }
 311
 312 /*
 313  *
 314  * hv_ringbuffer_get_debuginfo()
 315  *
 316  * Get various debug metrics for the specified ring buffer
 317  *
 318  */
 319 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 320                             struct hv_ring_buffer_debug_info *debug_info)
 321 {
 322         u32 bytes_avail_towrite;
 323         u32 bytes_avail_toread;
 324
 325         if (ring_info->ring_buffer) {
 326                 hv_get_ringbuffer_availbytes(ring_info,
 327                                         &bytes_avail_toread,
 328                                         &bytes_avail_towrite);
 329
 330                 debug_info->bytes_avail_toread = bytes_avail_toread;
 331                 debug_info->bytes_avail_towrite = bytes_avail_towrite;
 332                 debug_info->current_read_index =
 333                         ring_info->ring_buffer->read_index;
 334                 debug_info->current_write_index =
 335                         ring_info->ring_buffer->write_index;
 336                 debug_info->current_interrupt_mask =
 337                         ring_info->ring_buffer->interrupt_mask;
 338         }
 339 }
 340
 341 /*
 342  *
 343  * hv_ringbuffer_init()
 344  *
 345  *Initialize the ring buffer
 346  *
 347  */
 348 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 349                    void *buffer, u32 buflen)
 350 {
 351         if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
 352                 return -EINVAL;
 353
 354         memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
 355
 356         ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
 357         ring_info->ring_buffer->read_index =
 358                 ring_info->ring_buffer->write_index = 0;
 359
 360         ring_info->ring_size = buflen;
 361         ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
 362
 363         spin_lock_init(&ring_info->ring_lock);
 364
 365         return 0;
 366 }
 367
 368 /*
 369  *
 370  * hv_ringbuffer_cleanup()
 371  *
 372  * Cleanup the ring buffer
 373  *
 374  */
 375 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 376 {
 377 }
 378
 379 /*
 380  *
 381  * hv_ringbuffer_write()
 382  *
 383  * Write to the ring buffer
 384  *
 385  */
 386 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 387                     struct scatterlist *sglist, u32 sgcount, bool *signal)
 388 {
 389         int i = 0;
 390         u32 bytes_avail_towrite;
 391         u32 bytes_avail_toread;
 392         u32 totalbytes_towrite = 0;
 393
 394         struct scatterlist *sg;
 395         u32 next_write_location;
 396         u32 old_write;
 397         u64 prev_indices = 0;
 398         unsigned long flags;
 399
 400         for_each_sg(sglist, sg, sgcount, i)
 401         {
 402                 totalbytes_towrite += sg->length;
 403         }
 404
 405         totalbytes_towrite += sizeof(u64);
 406
 407         spin_lock_irqsave(&outring_info->ring_lock, flags);
 408
 409         hv_get_ringbuffer_availbytes(outring_info,
 410                                 &bytes_avail_toread,
 411                                 &bytes_avail_towrite);
 412
 413
 414         /* If there is only room for the packet, assume it is full. */
 415         /* Otherwise, the next time around, we think the ring buffer */
 416         /* is empty since the read index == write index */
 417         if (bytes_avail_towrite <= totalbytes_towrite) {
 418                 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 419                 return -EAGAIN;
 420         }
 421
 422         /* Write to the ring buffer */
 423         next_write_location = hv_get_next_write_location(outring_info);
 424
 425         old_write = next_write_location;
 426
 427         for_each_sg(sglist, sg, sgcount, i)
 428         {
 429                 next_write_location = hv_copyto_ringbuffer(outring_info,
 430                                                      next_write_location,
 431                                                      sg_virt(sg),
 432                                                      sg->length);
 433         }
 434
 435         /* Set previous packet start */
 436         prev_indices = hv_get_ring_bufferindices(outring_info);
 437
 438         next_write_location = hv_copyto_ringbuffer(outring_info,
 439                                              next_write_location,
 440                                              &prev_indices,
 441                                              sizeof(u64));
 442
 443         /* Issue a full memory barrier before updating the write index */
 444         smp_mb();
 445
 446         /* Now, update the write location */
 447         hv_set_next_write_location(outring_info, next_write_location);
 448
 449
 450         spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 451
 452         *signal = hv_need_to_signal(old_write, outring_info);
 453         return 0;
 454 }
 455
 456
 457 /*
 458  *
 459  * hv_ringbuffer_peek()
 460  *
 461  * Read without advancing the read index
 462  *
 463  */
 464 int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
 465                    void *Buffer, u32 buflen)
 466 {
 467         u32 bytes_avail_towrite;
 468         u32 bytes_avail_toread;
 469         u32 next_read_location = 0;
 470         unsigned long flags;
 471
 472         spin_lock_irqsave(&Inring_info->ring_lock, flags);
 473
 474         hv_get_ringbuffer_availbytes(Inring_info,
 475                                 &bytes_avail_toread,
 476                                 &bytes_avail_towrite);
 477
 478         /* Make sure there is something to read */
 479         if (bytes_avail_toread < buflen) {
 480
 481                 spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
 482
 483                 return -EAGAIN;
 484         }
 485
 486         /* Convert to byte offset */
 487         next_read_location = hv_get_next_read_location(Inring_info);
 488
 489         next_read_location = hv_copyfrom_ringbuffer(Inring_info,
 490                                                 Buffer,
 491                                                 buflen,
 492                                                 next_read_location);
 493
 494         spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
 495
 496         return 0;
 497 }
 498
 499
 500 /*
 501  *
 502  * hv_ringbuffer_read()
 503  *
 504  * Read and advance the read index
 505  *
 506  */
 507 int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 508                    u32 buflen, u32 offset, bool *signal)
 509 {
 510         u32 bytes_avail_towrite;
 511         u32 bytes_avail_toread;
 512         u32 next_read_location = 0;
 513         u64 prev_indices = 0;
 514         unsigned long flags;
 515         u32 old_read;
 516
 517         if (buflen <= 0)
 518                 return -EINVAL;
 519
 520         spin_lock_irqsave(&inring_info->ring_lock, flags);
 521
 522         hv_get_ringbuffer_availbytes(inring_info,
 523                                 &bytes_avail_toread,
 524                                 &bytes_avail_towrite);
 525
 526         old_read = bytes_avail_toread;
 527
 528         /* Make sure there is something to read */
 529         if (bytes_avail_toread < buflen) {
 530                 spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 531
 532                 return -EAGAIN;
 533         }
 534
 535         next_read_location =
 536                 hv_get_next_readlocation_withoffset(inring_info, offset);
 537
 538         next_read_location = hv_copyfrom_ringbuffer(inring_info,
 539                                                 buffer,
 540                                                 buflen,
 541                                                 next_read_location);
 542
 543         next_read_location = hv_copyfrom_ringbuffer(inring_info,
 544                                                 &prev_indices,
 545                                                 sizeof(u64),
 546                                                 next_read_location);
 547
 548         /* Make sure all reads are done before we update the read index since */
 549         /* the writer may start writing to the read area once the read index */
 550         /*is updated */
 551         smp_mb();
 552
 553         /* Update the read index */
 554         hv_set_next_read_location(inring_info, next_read_location);
 555
 556         spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 557
 558         *signal = hv_need_to_signal_on_read(old_read, inring_info);
 559
 560         return 0;
 561 }