include/ringbuffer/backend.h

   1 /* SPDX-License-Identifier: (GPL-2.0-only OR LGPL-2.1-only)
   2  *
   3  * ringbuffer/backend.h
   4  *
   5  * Ring buffer backend (API).
   6  *
   7  * Copyright (C) 2010-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   8  *
   9  * Credits to Steven Rostedt for proposing to use an extra-subbuffer owned by
  10  * the reader in flight recorder mode.
  11  */
  12
  13 #ifndef _LIB_RING_BUFFER_BACKEND_H
  14 #define _LIB_RING_BUFFER_BACKEND_H
  15
  16 #include <linux/types.h>
  17 #include <linux/sched.h>
  18 #include <linux/timer.h>
  19 #include <linux/wait.h>
  20 #include <linux/poll.h>
  21 #include <linux/list.h>
  22 #include <linux/fs.h>
  23 #include <linux/mm.h>
  24 #include <wrapper/uaccess.h>
  25 #include <lttng/probe-user.h>
  26
  27 /* Internal helpers */
  28 #include <ringbuffer/backend_internal.h>
  29 #include <ringbuffer/frontend_internal.h>
  30
  31 /* Ring buffer backend API */
  32
  33 /* Ring buffer backend access (read/write) */
  34
  35 extern size_t lib_ring_buffer_read(struct lttng_kernel_ring_buffer_backend *bufb,
  36                                    size_t offset, void *dest, size_t len);
  37
  38 extern int __lib_ring_buffer_copy_to_user(struct lttng_kernel_ring_buffer_backend *bufb,
  39                                           size_t offset, void __user *dest,
  40                                           size_t len);
  41
  42 extern int lib_ring_buffer_read_cstr(struct lttng_kernel_ring_buffer_backend *bufb,
  43                                      size_t offset, void *dest, size_t len);
  44
  45 extern unsigned long *
  46 lib_ring_buffer_read_get_pfn(struct lttng_kernel_ring_buffer_backend *bufb, size_t offset,
  47                               void ***virt);
  48
  49 /*
  50  * Return the address where a given offset is located.
  51  * Should be used to get the current subbuffer header pointer. Given we know
  52  * it's never on a page boundary, it's safe to write directly to this address,
  53  * as long as the write is never bigger than a page size.
  54  */
  55 extern void *
  56 lib_ring_buffer_offset_address(struct lttng_kernel_ring_buffer_backend *bufb,
  57                                size_t offset);
  58 extern void *
  59 lib_ring_buffer_read_offset_address(struct lttng_kernel_ring_buffer_backend *bufb,
  60                                     size_t offset);
  61
  62 /**
  63  * lib_ring_buffer_write - write data to a buffer backend
  64  * @config : ring buffer instance configuration
  65  * @ctx: ring buffer context. (input arguments only)
  66  * @src : source pointer to copy from
  67  * @len : length of data to copy
  68  *
  69  * This function copies "len" bytes of data from a source pointer to a buffer
  70  * backend, at the current context offset. This is more or less a buffer
  71  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  72  * if copy is crossing a page boundary.
  73  */
  74 static inline __attribute__((always_inline))
  75 void lib_ring_buffer_write(const struct lttng_kernel_ring_buffer_config *config,
  76                            struct lttng_kernel_ring_buffer_ctx *ctx,
  77                            const void *src, size_t len)
  78 {
  79         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
  80         struct channel_backend *chanb = &ctx->priv.chan->backend;
  81         size_t index, bytes_left_in_page;
  82         size_t offset = ctx->priv.buf_offset;
  83         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
  84
  85         if (unlikely(!len))
  86                 return;
  87         backend_pages =
  88                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
  89         offset &= chanb->buf_size - 1;
  90         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
  91         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
  92         if (likely(bytes_left_in_page == len))
  93                 lib_ring_buffer_do_copy(config,
  94                                         backend_pages->p[index].virt
  95                                             + (offset & ~PAGE_MASK),
  96                                         src, len);
  97         else
  98                 _lib_ring_buffer_write(bufb, offset, src, len);
  99         ctx->priv.buf_offset += len;
 100 }
 101
 102 /**
 103  * lib_ring_buffer_memset - write len bytes of c to a buffer backend
 104  * @config : ring buffer instance configuration
 105  * @bufb : ring buffer backend
 106  * @offset : offset within the buffer
 107  * @c : the byte to copy
 108  * @len : number of bytes to copy
 109  *
 110  * This function writes "len" bytes of "c" to a buffer backend, at a specific
 111  * offset. This is more or less a buffer backend-specific memset() operation.
 112  * Calls the slow path (_ring_buffer_memset) if write is crossing a page
 113  * boundary.
 114  */
 115 static inline
 116 void lib_ring_buffer_memset(const struct lttng_kernel_ring_buffer_config *config,
 117                             struct lttng_kernel_ring_buffer_ctx *ctx, int c, size_t len)
 118 {
 119
 120         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 121         struct channel_backend *chanb = &ctx->priv.chan->backend;
 122         size_t index, bytes_left_in_page;
 123         size_t offset = ctx->priv.buf_offset;
 124         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 125
 126         if (unlikely(!len))
 127                 return;
 128         backend_pages =
 129                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 130         offset &= chanb->buf_size - 1;
 131         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 132         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 133         if (likely(bytes_left_in_page == len))
 134                 lib_ring_buffer_do_memset(backend_pages->p[index].virt
 135                                           + (offset & ~PAGE_MASK),
 136                                           c, len);
 137         else
 138                 _lib_ring_buffer_memset(bufb, offset, c, len);
 139         ctx->priv.buf_offset += len;
 140 }
 141
 142 /*
 143  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 144  * terminating character is found in @src. Returns the number of bytes
 145  * copied. Does *not* terminate @dest with NULL terminating character.
 146  */
 147 static inline __attribute__((always_inline))
 148 size_t lib_ring_buffer_do_strcpy(const struct lttng_kernel_ring_buffer_config *config,
 149                 char *dest, const char *src, size_t len)
 150 {
 151         size_t count;
 152
 153         for (count = 0; count < len; count++) {
 154                 char c;
 155
 156                 /*
 157                  * Only read source character once, in case it is
 158                  * modified concurrently.
 159                  */
 160                 c = LTTNG_READ_ONCE(src[count]);
 161                 if (!c)
 162                         break;
 163                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 164         }
 165         return count;
 166 }
 167
 168 /*
 169  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 170  * terminating character is found in @src, or when a fault occurs.
 171  * Returns the number of bytes copied. Does *not* terminate @dest with
 172  * NULL terminating character.
 173  *
 174  * This function deals with userspace pointers, it should never be called
 175  * directly without having the src pointer checked with access_ok()
 176  * previously.
 177  */
 178 static inline __attribute__((always_inline))
 179 size_t lib_ring_buffer_do_strcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 180                 char *dest, const char __user *src, size_t len)
 181 {
 182         size_t count;
 183
 184         for (count = 0; count < len; count++) {
 185                 int ret;
 186                 char c;
 187
 188                 ret = __copy_from_user_inatomic(&c, src + count, 1);
 189                 if (ret || !c)
 190                         break;
 191                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 192         }
 193         return count;
 194 }
 195
 196 /**
 197  * lib_ring_buffer_strcpy - write string data to a buffer backend
 198  * @config : ring buffer instance configuration
 199  * @ctx: ring buffer context. (input arguments only)
 200  * @src : source pointer to copy from
 201  * @len : length of data to copy
 202  * @pad : character to use for padding
 203  *
 204  * This function copies @len - 1 bytes of string data from a source
 205  * pointer to a buffer backend, followed by a terminating '\0'
 206  * character, at the current context offset. This is more or less a
 207  * buffer backend-specific strncpy() operation. If a terminating '\0'
 208  * character is found in @src before @len - 1 characters are copied, pad
 209  * the buffer with @pad characters (e.g. '#'). Calls the slow path
 210  * (_ring_buffer_strcpy) if copy is crossing a page boundary.
 211  */
 212 static inline
 213 void lib_ring_buffer_strcpy(const struct lttng_kernel_ring_buffer_config *config,
 214                            struct lttng_kernel_ring_buffer_ctx *ctx,
 215                            const char *src, size_t len, int pad)
 216 {
 217         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 218         struct channel_backend *chanb = &ctx->priv.chan->backend;
 219         size_t index, bytes_left_in_page;
 220         size_t offset = ctx->priv.buf_offset;
 221         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 222
 223         if (unlikely(!len))
 224                 return;
 225         backend_pages =
 226                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 227         offset &= chanb->buf_size - 1;
 228         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 229         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 230         if (likely(bytes_left_in_page == len)) {
 231                 size_t count;
 232
 233                 count = lib_ring_buffer_do_strcpy(config,
 234                                         backend_pages->p[index].virt
 235                                             + (offset & ~PAGE_MASK),
 236                                         src, len - 1);
 237                 offset += count;
 238                 /* Padding */
 239                 if (unlikely(count < len - 1)) {
 240                         size_t pad_len = len - 1 - count;
 241
 242                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 243                                                 + (offset & ~PAGE_MASK),
 244                                         pad, pad_len);
 245                         offset += pad_len;
 246                 }
 247                 /* Ending '\0' */
 248                 lib_ring_buffer_do_memset(backend_pages->p[index].virt
 249                                         + (offset & ~PAGE_MASK),
 250                                 '\0', 1);
 251         } else {
 252                 _lib_ring_buffer_strcpy(bufb, offset, src, len, pad);
 253         }
 254         ctx->priv.buf_offset += len;
 255 }
 256
 257 /**
 258  * lib_ring_buffer_pstrcpy - write kernel C-string (input) to a buffer backend P-string
 259  * @config : ring buffer instance configuration
 260  * @ctx: ring buffer context. (input arguments only)
 261  * @src : source pointer to copy from
 262  * @len : length of data to copy
 263  * @pad : character to use for padding
 264  *
 265  * This function copies up to @len bytes of data from a source pointer
 266  * to a Pascal String into the buffer backend. If a terminating '\0'
 267  * character is found in @src before @len characters are copied, pad the
 268  * buffer with @pad characters (e.g. '\0').
 269  *
 270  * The length of the pascal strings in the ring buffer is explicit: it
 271  * is either the array or sequence length.
 272  */
 273 static inline
 274 void lib_ring_buffer_pstrcpy(const struct lttng_kernel_ring_buffer_config *config,
 275                            struct lttng_kernel_ring_buffer_ctx *ctx,
 276                            const char *src, size_t len, char pad)
 277         __attribute__((always_inline));
 278 static inline
 279 void lib_ring_buffer_pstrcpy(const struct lttng_kernel_ring_buffer_config *config,
 280                            struct lttng_kernel_ring_buffer_ctx *ctx,
 281                            const char *src, size_t len, char pad)
 282 {
 283         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 284         struct channel_backend *chanb = &ctx->priv.chan->backend;
 285         size_t index, bytes_left_in_page;
 286         size_t offset = ctx->priv.buf_offset;
 287         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 288
 289         if (unlikely(!len))
 290                 return;
 291         backend_pages =
 292                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 293         offset &= chanb->buf_size - 1;
 294         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 295         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 296         if (likely(bytes_left_in_page == len)) {
 297                 size_t count;
 298
 299                 count = lib_ring_buffer_do_strcpy(config,
 300                                         backend_pages->p[index].virt
 301                                             + (offset & ~PAGE_MASK),
 302                                         src, len);
 303                 offset += count;
 304                 /* Padding */
 305                 if (unlikely(count < len)) {
 306                         size_t pad_len = len - count;
 307
 308                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 309                                                 + (offset & ~PAGE_MASK),
 310                                         pad, pad_len);
 311                         offset += pad_len;
 312                 }
 313         } else {
 314                 _lib_ring_buffer_pstrcpy(bufb, offset, src, len, pad);
 315         }
 316         ctx->priv.buf_offset += len;
 317 }
 318
 319 /**
 320  * lib_ring_buffer_copy_from_user_inatomic - write userspace data to a buffer backend
 321  * @config : ring buffer instance configuration
 322  * @ctx: ring buffer context. (input arguments only)
 323  * @src : userspace source pointer to copy from
 324  * @len : length of data to copy
 325  *
 326  * This function copies "len" bytes of data from a userspace pointer to a
 327  * buffer backend, at the current context offset. This is more or less a buffer
 328  * backend-specific memcpy() operation. Calls the slow path
 329  * (_ring_buffer_write_from_user_inatomic) if copy is crossing a page boundary.
 330  * Disable the page fault handler to ensure we never try to take the mmap_sem.
 331  */
 332 static inline __attribute__((always_inline))
 333 void lib_ring_buffer_copy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 334                                     struct lttng_kernel_ring_buffer_ctx *ctx,
 335                                     const void __user *src, size_t len)
 336 {
 337         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 338         struct channel_backend *chanb = &ctx->priv.chan->backend;
 339         size_t index, bytes_left_in_page;
 340         size_t offset = ctx->priv.buf_offset;
 341         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 342         unsigned long ret;
 343
 344         if (unlikely(!len))
 345                 return;
 346         backend_pages =
 347                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 348         offset &= chanb->buf_size - 1;
 349         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 350         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 351
 352         if (unlikely(!lttng_access_ok(VERIFY_READ, src, len)))
 353                 goto fill_buffer;
 354
 355         pagefault_disable();
 356         if (likely(bytes_left_in_page == len)) {
 357                 ret = lib_ring_buffer_do_copy_from_user_inatomic(
 358                         backend_pages->p[index].virt + (offset & ~PAGE_MASK),
 359                         src, len);
 360                 if (unlikely(ret > 0)) {
 361                         /* Copy failed. */
 362                         goto fill_buffer_enable_pf;
 363                 }
 364         } else {
 365                 _lib_ring_buffer_copy_from_user_inatomic(bufb, offset, src, len);
 366         }
 367         pagefault_enable();
 368         ctx->priv.buf_offset += len;
 369
 370         return;
 371
 372 fill_buffer_enable_pf:
 373         pagefault_enable();
 374 fill_buffer:
 375         /*
 376          * In the error path we call the slow path version to avoid
 377          * the pollution of static inline code.
 378          */
 379         _lib_ring_buffer_memset(bufb, offset, 0, len);
 380         ctx->priv.buf_offset += len;
 381 }
 382
 383 /**
 384  * lib_ring_buffer_strcpy_from_user_inatomic - write userspace string data to a buffer backend
 385  * @config : ring buffer instance configuration
 386  * @ctx: ring buffer context (input arguments only)
 387  * @src : userspace source pointer to copy from
 388  * @len : length of data to copy
 389  * @pad : character to use for padding
 390  *
 391  * This function copies @len - 1 bytes of string data from a userspace
 392  * source pointer to a buffer backend, followed by a terminating '\0'
 393  * character, at the current context offset. This is more or less a
 394  * buffer backend-specific strncpy() operation. If a terminating '\0'
 395  * character is found in @src before @len - 1 characters are copied, pad
 396  * the buffer with @pad characters (e.g. '#'). Calls the slow path
 397  * (_ring_buffer_strcpy_from_user_inatomic) if copy is crossing a page
 398  * boundary. Disable the page fault handler to ensure we never try to
 399  * take the mmap_sem.
 400  */
 401 static inline
 402 void lib_ring_buffer_strcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 403                 struct lttng_kernel_ring_buffer_ctx *ctx,
 404                 const void __user *src, size_t len, int pad)
 405 {
 406         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 407         struct channel_backend *chanb = &ctx->priv.chan->backend;
 408         size_t index, bytes_left_in_page;
 409         size_t offset = ctx->priv.buf_offset;
 410         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 411
 412         if (unlikely(!len))
 413                 return;
 414         backend_pages =
 415                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 416         offset &= chanb->buf_size - 1;
 417         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 418         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 419
 420         if (unlikely(!lttng_access_ok(VERIFY_READ, src, len)))
 421                 goto fill_buffer;
 422
 423         pagefault_disable();
 424         if (likely(bytes_left_in_page == len)) {
 425                 size_t count;
 426
 427                 count = lib_ring_buffer_do_strcpy_from_user_inatomic(config,
 428                                         backend_pages->p[index].virt
 429                                             + (offset & ~PAGE_MASK),
 430                                         src, len - 1);
 431                 offset += count;
 432                 /* Padding */
 433                 if (unlikely(count < len - 1)) {
 434                         size_t pad_len = len - 1 - count;
 435
 436                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 437                                                 + (offset & ~PAGE_MASK),
 438                                         pad, pad_len);
 439                         offset += pad_len;
 440                 }
 441                 /* Ending '\0' */
 442                 lib_ring_buffer_do_memset(backend_pages->p[index].virt
 443                                         + (offset & ~PAGE_MASK),
 444                                 '\0', 1);
 445         } else {
 446                 _lib_ring_buffer_strcpy_from_user_inatomic(bufb, offset, src,
 447                                         len, pad);
 448         }
 449         pagefault_enable();
 450         ctx->priv.buf_offset += len;
 451
 452         return;
 453
 454 fill_buffer:
 455         /*
 456          * In the error path we call the slow path version to avoid
 457          * the pollution of static inline code.
 458          */
 459         _lib_ring_buffer_memset(bufb, offset, pad, len - 1);
 460         offset += len - 1;
 461         _lib_ring_buffer_memset(bufb, offset, '\0', 1);
 462         ctx->priv.buf_offset += len;
 463 }
 464
 465 /**
 466  * lib_ring_buffer_pstrcpy_from_user_inatomic - write user-space C-string (input) to a buffer backend P-string
 467  * @config : ring buffer instance configuration
 468  * @ctx: ring buffer context. (input arguments only)
 469  * @src : source pointer to copy from
 470  * @len : length of data to copy
 471  * @pad : character to use for padding
 472  *
 473  * This function copies up to @len bytes of data from a source pointer
 474  * to a Pascal String into the buffer backend. If a terminating '\0'
 475  * character is found in @src before @len characters are copied, pad the
 476  * buffer with @pad characters (e.g. '\0').
 477  *
 478  * The length of the pascal strings in the ring buffer is explicit: it
 479  * is either the array or sequence length.
 480  */
 481 static inline
 482 void lib_ring_buffer_pstrcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 483                            struct lttng_kernel_ring_buffer_ctx *ctx,
 484                            const char __user *src, size_t len, char pad)
 485         __attribute__((always_inline));
 486 static inline
 487 void lib_ring_buffer_pstrcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 488                            struct lttng_kernel_ring_buffer_ctx *ctx,
 489                            const char __user *src, size_t len, char pad)
 490 {
 491         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 492         struct channel_backend *chanb = &ctx->priv.chan->backend;
 493         size_t index, bytes_left_in_page;
 494         size_t offset = ctx->priv.buf_offset;
 495         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 496
 497         if (unlikely(!len))
 498                 return;
 499         backend_pages =
 500                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 501         offset &= chanb->buf_size - 1;
 502         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 503         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 504
 505         if (unlikely(!lttng_access_ok(VERIFY_READ, src, len)))
 506                 goto fill_buffer;
 507
 508         pagefault_disable();
 509         if (likely(bytes_left_in_page == len)) {
 510                 size_t count;
 511
 512                 count = lib_ring_buffer_do_strcpy_from_user_inatomic(config,
 513                                         backend_pages->p[index].virt
 514                                             + (offset & ~PAGE_MASK),
 515                                         src, len);
 516                 offset += count;
 517                 /* Padding */
 518                 if (unlikely(count < len)) {
 519                         size_t pad_len = len - count;
 520
 521                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 522                                                 + (offset & ~PAGE_MASK),
 523                                         pad, pad_len);
 524                         offset += pad_len;
 525                 }
 526         } else {
 527                 _lib_ring_buffer_pstrcpy_from_user_inatomic(bufb, offset, src, len, pad);
 528         }
 529         ctx->priv.buf_offset += len;
 530         pagefault_enable();
 531
 532         return;
 533
 534 fill_buffer:
 535         /*
 536          * In the error path we call the slow path version to avoid
 537          * the pollution of static inline code.
 538          */
 539         _lib_ring_buffer_memset(bufb, offset, pad, len);
 540         ctx->priv.buf_offset += len;
 541 }
 542
 543 /*
 544  * This accessor counts the number of unread records in a buffer.
 545  * It only provides a consistent value if no reads not writes are performed
 546  * concurrently.
 547  */
 548 static inline
 549 unsigned long lib_ring_buffer_get_records_unread(
 550                                 const struct lttng_kernel_ring_buffer_config *config,
 551                                 struct lttng_kernel_ring_buffer *buf)
 552 {
 553         struct lttng_kernel_ring_buffer_backend *bufb = &buf->backend;
 554         struct lttng_kernel_ring_buffer_backend_pages *pages;
 555         unsigned long records_unread = 0, sb_bindex, id;
 556         unsigned int i;
 557
 558         for (i = 0; i < bufb->chan->backend.num_subbuf; i++) {
 559                 id = bufb->buf_wsb[i].id;
 560                 sb_bindex = subbuffer_id_get_index(config, id);
 561                 pages = bufb->array[sb_bindex];
 562                 records_unread += v_read(config, &pages->records_unread);
 563         }
 564         if (config->mode == RING_BUFFER_OVERWRITE) {
 565                 id = bufb->buf_rsb.id;
 566                 sb_bindex = subbuffer_id_get_index(config, id);
 567                 pages = bufb->array[sb_bindex];
 568                 records_unread += v_read(config, &pages->records_unread);
 569         }
 570         return records_unread;
 571 }
 572
 573 /*
 574  * We use __copy_from_user_inatomic to copy userspace data after
 575  * checking with access_ok() and disabling page faults.
 576  *
 577  * Return 0 if OK, nonzero on error.
 578  */
 579 static inline
 580 unsigned long lib_ring_buffer_copy_from_user_check_nofault(void *dest,
 581                                                 const void __user *src,
 582                                                 unsigned long len)
 583 {
 584         return lttng_copy_from_user_check_nofault(dest, src, len);
 585 }
 586
 587 #endif /* _LIB_RING_BUFFER_BACKEND_H */