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         /* check interrupt_mask before read_index */
  79         rmb();
  80         /*
  81          * This is the only case we need to signal when the
  82          * ring transitions from being empty to non-empty.
  83          */
  84         if (old_write == rbi->ring_buffer->read_index)
  85                 return true;
  86
  87         return false;
  88 }
  89
  90 /*
  91  * To optimize the flow management on the send-side,
  92  * when the sender is blocked because of lack of
  93  * sufficient space in the ring buffer, potential the
  94  * consumer of the ring buffer can signal the producer.
  95  * This is controlled by the following parameters:
  96  *
  97  * 1. pending_send_sz: This is the size in bytes that the
  98  *    producer is trying to send.
  99  * 2. The feature bit feat_pending_send_sz set to indicate if
 100  *    the consumer of the ring will signal when the ring
 101  *    state transitions from being full to a state where
 102  *    there is room for the producer to send the pending packet.
 103  */
 104
 105 static bool hv_need_to_signal_on_read(u32 old_rd,
 106                                          struct hv_ring_buffer_info *rbi)
 107 {
 108         u32 prev_write_sz;
 109         u32 cur_write_sz;
 110         u32 r_size;
 111         u32 write_loc = rbi->ring_buffer->write_index;
 112         u32 read_loc = rbi->ring_buffer->read_index;
 113         u32 pending_sz = rbi->ring_buffer->pending_send_sz;
 114
 115         /*
 116          * If the other end is not blocked on write don't bother.
 117          */
 118         if (pending_sz == 0)
 119                 return false;
 120
 121         r_size = rbi->ring_datasize;
 122         cur_write_sz = write_loc >= read_loc ? r_size - (write_loc - read_loc) :
 123                         read_loc - write_loc;
 124
 125         prev_write_sz = write_loc >= old_rd ? r_size - (write_loc - old_rd) :
 126                         old_rd - write_loc;
 127
 128
 129         if ((prev_write_sz < pending_sz) && (cur_write_sz >= pending_sz))
 130                 return true;
 131
 132         return false;
 133 }
 134
 135 /*
 136  * hv_get_next_write_location()
 137  *
 138  * Get the next write location for the specified ring buffer
 139  *
 140  */
 141 static inline u32
 142 hv_get_next_write_location(struct hv_ring_buffer_info *ring_info)
 143 {
 144         u32 next = ring_info->ring_buffer->write_index;
 145
 146         return next;
 147 }
 148
 149 /*
 150  * hv_set_next_write_location()
 151  *
 152  * Set the next write location for the specified ring buffer
 153  *
 154  */
 155 static inline void
 156 hv_set_next_write_location(struct hv_ring_buffer_info *ring_info,
 157                      u32 next_write_location)
 158 {
 159         ring_info->ring_buffer->write_index = next_write_location;
 160 }
 161
 162 /*
 163  * hv_get_next_read_location()
 164  *
 165  * Get the next read location for the specified ring buffer
 166  */
 167 static inline u32
 168 hv_get_next_read_location(struct hv_ring_buffer_info *ring_info)
 169 {
 170         u32 next = ring_info->ring_buffer->read_index;
 171
 172         return next;
 173 }
 174
 175 /*
 176  * hv_get_next_readlocation_withoffset()
 177  *
 178  * Get the next read location + offset for the specified ring buffer.
 179  * This allows the caller to skip
 180  */
 181 static inline u32
 182 hv_get_next_readlocation_withoffset(struct hv_ring_buffer_info *ring_info,
 183                                  u32 offset)
 184 {
 185         u32 next = ring_info->ring_buffer->read_index;
 186
 187         next += offset;
 188         next %= ring_info->ring_datasize;
 189
 190         return next;
 191 }
 192
 193 /*
 194  *
 195  * hv_set_next_read_location()
 196  *
 197  * Set the next read location for the specified ring buffer
 198  *
 199  */
 200 static inline void
 201 hv_set_next_read_location(struct hv_ring_buffer_info *ring_info,
 202                     u32 next_read_location)
 203 {
 204         ring_info->ring_buffer->read_index = next_read_location;
 205 }
 206
 207
 208 /*
 209  *
 210  * hv_get_ring_buffer()
 211  *
 212  * Get the start of the ring buffer
 213  */
 214 static inline void *
 215 hv_get_ring_buffer(struct hv_ring_buffer_info *ring_info)
 216 {
 217         return (void *)ring_info->ring_buffer->buffer;
 218 }
 219
 220
 221 /*
 222  *
 223  * hv_get_ring_buffersize()
 224  *
 225  * Get the size of the ring buffer
 226  */
 227 static inline u32
 228 hv_get_ring_buffersize(struct hv_ring_buffer_info *ring_info)
 229 {
 230         return ring_info->ring_datasize;
 231 }
 232
 233 /*
 234  *
 235  * hv_get_ring_bufferindices()
 236  *
 237  * Get the read and write indices as u64 of the specified ring buffer
 238  *
 239  */
 240 static inline u64
 241 hv_get_ring_bufferindices(struct hv_ring_buffer_info *ring_info)
 242 {
 243         return (u64)ring_info->ring_buffer->write_index << 32;
 244 }
 245
 246 /*
 247  *
 248  * hv_copyfrom_ringbuffer()
 249  *
 250  * Helper routine to copy to source from ring buffer.
 251  * Assume there is enough room. Handles wrap-around in src case only!!
 252  *
 253  */
 254 static u32 hv_copyfrom_ringbuffer(
 255         struct hv_ring_buffer_info      *ring_info,
 256         void                            *dest,
 257         u32                             destlen,
 258         u32                             start_read_offset)
 259 {
 260         void *ring_buffer = hv_get_ring_buffer(ring_info);
 261         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 262
 263         u32 frag_len;
 264
 265         /* wrap-around detected at the src */
 266         if (destlen > ring_buffer_size - start_read_offset) {
 267                 frag_len = ring_buffer_size - start_read_offset;
 268
 269                 memcpy(dest, ring_buffer + start_read_offset, frag_len);
 270                 memcpy(dest + frag_len, ring_buffer, destlen - frag_len);
 271         } else
 272
 273                 memcpy(dest, ring_buffer + start_read_offset, destlen);
 274
 275
 276         start_read_offset += destlen;
 277         start_read_offset %= ring_buffer_size;
 278
 279         return start_read_offset;
 280 }
 281
 282
 283 /*
 284  *
 285  * hv_copyto_ringbuffer()
 286  *
 287  * Helper routine to copy from source to ring buffer.
 288  * Assume there is enough room. Handles wrap-around in dest case only!!
 289  *
 290  */
 291 static u32 hv_copyto_ringbuffer(
 292         struct hv_ring_buffer_info      *ring_info,
 293         u32                             start_write_offset,
 294         void                            *src,
 295         u32                             srclen)
 296 {
 297         void *ring_buffer = hv_get_ring_buffer(ring_info);
 298         u32 ring_buffer_size = hv_get_ring_buffersize(ring_info);
 299         u32 frag_len;
 300
 301         /* wrap-around detected! */
 302         if (srclen > ring_buffer_size - start_write_offset) {
 303                 frag_len = ring_buffer_size - start_write_offset;
 304                 memcpy(ring_buffer + start_write_offset, src, frag_len);
 305                 memcpy(ring_buffer, src + frag_len, srclen - frag_len);
 306         } else
 307                 memcpy(ring_buffer + start_write_offset, src, srclen);
 308
 309         start_write_offset += srclen;
 310         start_write_offset %= ring_buffer_size;
 311
 312         return start_write_offset;
 313 }
 314
 315 /*
 316  *
 317  * hv_ringbuffer_get_debuginfo()
 318  *
 319  * Get various debug metrics for the specified ring buffer
 320  *
 321  */
 322 void hv_ringbuffer_get_debuginfo(struct hv_ring_buffer_info *ring_info,
 323                             struct hv_ring_buffer_debug_info *debug_info)
 324 {
 325         u32 bytes_avail_towrite;
 326         u32 bytes_avail_toread;
 327
 328         if (ring_info->ring_buffer) {
 329                 hv_get_ringbuffer_availbytes(ring_info,
 330                                         &bytes_avail_toread,
 331                                         &bytes_avail_towrite);
 332
 333                 debug_info->bytes_avail_toread = bytes_avail_toread;
 334                 debug_info->bytes_avail_towrite = bytes_avail_towrite;
 335                 debug_info->current_read_index =
 336                         ring_info->ring_buffer->read_index;
 337                 debug_info->current_write_index =
 338                         ring_info->ring_buffer->write_index;
 339                 debug_info->current_interrupt_mask =
 340                         ring_info->ring_buffer->interrupt_mask;
 341         }
 342 }
 343
 344 /*
 345  *
 346  * hv_ringbuffer_init()
 347  *
 348  *Initialize the ring buffer
 349  *
 350  */
 351 int hv_ringbuffer_init(struct hv_ring_buffer_info *ring_info,
 352                    void *buffer, u32 buflen)
 353 {
 354         if (sizeof(struct hv_ring_buffer) != PAGE_SIZE)
 355                 return -EINVAL;
 356
 357         memset(ring_info, 0, sizeof(struct hv_ring_buffer_info));
 358
 359         ring_info->ring_buffer = (struct hv_ring_buffer *)buffer;
 360         ring_info->ring_buffer->read_index =
 361                 ring_info->ring_buffer->write_index = 0;
 362
 363         ring_info->ring_size = buflen;
 364         ring_info->ring_datasize = buflen - sizeof(struct hv_ring_buffer);
 365
 366         spin_lock_init(&ring_info->ring_lock);
 367
 368         return 0;
 369 }
 370
 371 /*
 372  *
 373  * hv_ringbuffer_cleanup()
 374  *
 375  * Cleanup the ring buffer
 376  *
 377  */
 378 void hv_ringbuffer_cleanup(struct hv_ring_buffer_info *ring_info)
 379 {
 380 }
 381
 382 /*
 383  *
 384  * hv_ringbuffer_write()
 385  *
 386  * Write to the ring buffer
 387  *
 388  */
 389 int hv_ringbuffer_write(struct hv_ring_buffer_info *outring_info,
 390                     struct scatterlist *sglist, u32 sgcount, bool *signal)
 391 {
 392         int i = 0;
 393         u32 bytes_avail_towrite;
 394         u32 bytes_avail_toread;
 395         u32 totalbytes_towrite = 0;
 396
 397         struct scatterlist *sg;
 398         u32 next_write_location;
 399         u32 old_write;
 400         u64 prev_indices = 0;
 401         unsigned long flags;
 402
 403         for_each_sg(sglist, sg, sgcount, i)
 404         {
 405                 totalbytes_towrite += sg->length;
 406         }
 407
 408         totalbytes_towrite += sizeof(u64);
 409
 410         spin_lock_irqsave(&outring_info->ring_lock, flags);
 411
 412         hv_get_ringbuffer_availbytes(outring_info,
 413                                 &bytes_avail_toread,
 414                                 &bytes_avail_towrite);
 415
 416
 417         /* If there is only room for the packet, assume it is full. */
 418         /* Otherwise, the next time around, we think the ring buffer */
 419         /* is empty since the read index == write index */
 420         if (bytes_avail_towrite <= totalbytes_towrite) {
 421                 spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 422                 return -EAGAIN;
 423         }
 424
 425         /* Write to the ring buffer */
 426         next_write_location = hv_get_next_write_location(outring_info);
 427
 428         old_write = next_write_location;
 429
 430         for_each_sg(sglist, sg, sgcount, i)
 431         {
 432                 next_write_location = hv_copyto_ringbuffer(outring_info,
 433                                                      next_write_location,
 434                                                      sg_virt(sg),
 435                                                      sg->length);
 436         }
 437
 438         /* Set previous packet start */
 439         prev_indices = hv_get_ring_bufferindices(outring_info);
 440
 441         next_write_location = hv_copyto_ringbuffer(outring_info,
 442                                              next_write_location,
 443                                              &prev_indices,
 444                                              sizeof(u64));
 445
 446         /* Issue a full memory barrier before updating the write index */
 447         mb();
 448
 449         /* Now, update the write location */
 450         hv_set_next_write_location(outring_info, next_write_location);
 451
 452
 453         spin_unlock_irqrestore(&outring_info->ring_lock, flags);
 454
 455         *signal = hv_need_to_signal(old_write, outring_info);
 456         return 0;
 457 }
 458
 459
 460 /*
 461  *
 462  * hv_ringbuffer_peek()
 463  *
 464  * Read without advancing the read index
 465  *
 466  */
 467 int hv_ringbuffer_peek(struct hv_ring_buffer_info *Inring_info,
 468                    void *Buffer, u32 buflen)
 469 {
 470         u32 bytes_avail_towrite;
 471         u32 bytes_avail_toread;
 472         u32 next_read_location = 0;
 473         unsigned long flags;
 474
 475         spin_lock_irqsave(&Inring_info->ring_lock, flags);
 476
 477         hv_get_ringbuffer_availbytes(Inring_info,
 478                                 &bytes_avail_toread,
 479                                 &bytes_avail_towrite);
 480
 481         /* Make sure there is something to read */
 482         if (bytes_avail_toread < buflen) {
 483
 484                 spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
 485
 486                 return -EAGAIN;
 487         }
 488
 489         /* Convert to byte offset */
 490         next_read_location = hv_get_next_read_location(Inring_info);
 491
 492         next_read_location = hv_copyfrom_ringbuffer(Inring_info,
 493                                                 Buffer,
 494                                                 buflen,
 495                                                 next_read_location);
 496
 497         spin_unlock_irqrestore(&Inring_info->ring_lock, flags);
 498
 499         return 0;
 500 }
 501
 502
 503 /*
 504  *
 505  * hv_ringbuffer_read()
 506  *
 507  * Read and advance the read index
 508  *
 509  */
 510 int hv_ringbuffer_read(struct hv_ring_buffer_info *inring_info, void *buffer,
 511                    u32 buflen, u32 offset, bool *signal)
 512 {
 513         u32 bytes_avail_towrite;
 514         u32 bytes_avail_toread;
 515         u32 next_read_location = 0;
 516         u64 prev_indices = 0;
 517         unsigned long flags;
 518         u32 old_read;
 519
 520         if (buflen <= 0)
 521                 return -EINVAL;
 522
 523         spin_lock_irqsave(&inring_info->ring_lock, flags);
 524
 525         hv_get_ringbuffer_availbytes(inring_info,
 526                                 &bytes_avail_toread,
 527                                 &bytes_avail_towrite);
 528
 529         old_read = bytes_avail_toread;
 530
 531         /* Make sure there is something to read */
 532         if (bytes_avail_toread < buflen) {
 533                 spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 534
 535                 return -EAGAIN;
 536         }
 537
 538         next_read_location =
 539                 hv_get_next_readlocation_withoffset(inring_info, offset);
 540
 541         next_read_location = hv_copyfrom_ringbuffer(inring_info,
 542                                                 buffer,
 543                                                 buflen,
 544                                                 next_read_location);
 545
 546         next_read_location = hv_copyfrom_ringbuffer(inring_info,
 547                                                 &prev_indices,
 548                                                 sizeof(u64),
 549                                                 next_read_location);
 550
 551         /* Make sure all reads are done before we update the read index since */
 552         /* the writer may start writing to the read area once the read index */
 553         /*is updated */
 554         mb();
 555
 556         /* Update the read index */
 557         hv_set_next_read_location(inring_info, next_read_location);
 558
 559         spin_unlock_irqrestore(&inring_info->ring_lock, flags);
 560
 561         *signal = hv_need_to_signal_on_read(old_read, inring_info);
 562
 563         return 0;
 564 }