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
  26 /* Internal helpers */
  27 #include <ringbuffer/backend_internal.h>
  28 #include <ringbuffer/frontend_internal.h>
  29
  30 /* Ring buffer backend API */
  31
  32 /* Ring buffer backend access (read/write) */
  33
  34 extern size_t lib_ring_buffer_read(struct lttng_kernel_ring_buffer_backend *bufb,
  35                                    size_t offset, void *dest, size_t len);
  36
  37 extern int __lib_ring_buffer_copy_to_user(struct lttng_kernel_ring_buffer_backend *bufb,
  38                                           size_t offset, void __user *dest,
  39                                           size_t len);
  40
  41 extern int lib_ring_buffer_read_cstr(struct lttng_kernel_ring_buffer_backend *bufb,
  42                                      size_t offset, void *dest, size_t len);
  43
  44 extern unsigned long *
  45 lib_ring_buffer_read_get_pfn(struct lttng_kernel_ring_buffer_backend *bufb, size_t offset,
  46                               void ***virt);
  47
  48 /*
  49  * Return the address where a given offset is located.
  50  * Should be used to get the current subbuffer header pointer. Given we know
  51  * it's never on a page boundary, it's safe to write directly to this address,
  52  * as long as the write is never bigger than a page size.
  53  */
  54 extern void *
  55 lib_ring_buffer_offset_address(struct lttng_kernel_ring_buffer_backend *bufb,
  56                                size_t offset);
  57 extern void *
  58 lib_ring_buffer_read_offset_address(struct lttng_kernel_ring_buffer_backend *bufb,
  59                                     size_t offset);
  60
  61 /**
  62  * lib_ring_buffer_write - write data to a buffer backend
  63  * @config : ring buffer instance configuration
  64  * @ctx: ring buffer context. (input arguments only)
  65  * @src : source pointer to copy from
  66  * @len : length of data to copy
  67  *
  68  * This function copies "len" bytes of data from a source pointer to a buffer
  69  * backend, at the current context offset. This is more or less a buffer
  70  * backend-specific memcpy() operation. Calls the slow path (_ring_buffer_write)
  71  * if copy is crossing a page boundary.
  72  */
  73 static inline __attribute__((always_inline))
  74 void lib_ring_buffer_write(const struct lttng_kernel_ring_buffer_config *config,
  75                            struct lttng_kernel_ring_buffer_ctx *ctx,
  76                            const void *src, size_t len)
  77 {
  78         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
  79         struct channel_backend *chanb = &ctx->priv.chan->backend;
  80         size_t index, pagecpy;
  81         size_t offset = ctx->priv.buf_offset;
  82         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
  83
  84         if (unlikely(!len))
  85                 return;
  86         backend_pages =
  87                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
  88         offset &= chanb->buf_size - 1;
  89         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
  90         pagecpy = min_t(size_t, len, (-offset) & ~PAGE_MASK);
  91         if (likely(pagecpy == len))
  92                 lib_ring_buffer_do_copy(config,
  93                                         backend_pages->p[index].virt
  94                                             + (offset & ~PAGE_MASK),
  95                                         src, len);
  96         else
  97                 _lib_ring_buffer_write(bufb, offset, src, len, 0);
  98         ctx->priv.buf_offset += len;
  99 }
 100
 101 /**
 102  * lib_ring_buffer_memset - write len bytes of c to a buffer backend
 103  * @config : ring buffer instance configuration
 104  * @bufb : ring buffer backend
 105  * @offset : offset within the buffer
 106  * @c : the byte to copy
 107  * @len : number of bytes to copy
 108  *
 109  * This function writes "len" bytes of "c" to a buffer backend, at a specific
 110  * offset. This is more or less a buffer backend-specific memset() operation.
 111  * Calls the slow path (_ring_buffer_memset) if write is crossing a page
 112  * boundary.
 113  */
 114 static inline
 115 void lib_ring_buffer_memset(const struct lttng_kernel_ring_buffer_config *config,
 116                             struct lttng_kernel_ring_buffer_ctx *ctx, int c, size_t len)
 117 {
 118
 119         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 120         struct channel_backend *chanb = &ctx->priv.chan->backend;
 121         size_t index, pagecpy;
 122         size_t offset = ctx->priv.buf_offset;
 123         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 124
 125         if (unlikely(!len))
 126                 return;
 127         backend_pages =
 128                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 129         offset &= chanb->buf_size - 1;
 130         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 131         pagecpy = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 132         if (likely(pagecpy == len))
 133                 lib_ring_buffer_do_memset(backend_pages->p[index].virt
 134                                           + (offset & ~PAGE_MASK),
 135                                           c, len);
 136         else
 137                 _lib_ring_buffer_memset(bufb, offset, c, len, 0);
 138         ctx->priv.buf_offset += len;
 139 }
 140
 141 /*
 142  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 143  * terminating character is found in @src. Returns the number of bytes
 144  * copied. Does *not* terminate @dest with NULL terminating character.
 145  */
 146 static inline __attribute__((always_inline))
 147 size_t lib_ring_buffer_do_strcpy(const struct lttng_kernel_ring_buffer_config *config,
 148                 char *dest, const char *src, size_t len)
 149 {
 150         size_t count;
 151
 152         for (count = 0; count < len; count++) {
 153                 char c;
 154
 155                 /*
 156                  * Only read source character once, in case it is
 157                  * modified concurrently.
 158                  */
 159                 c = LTTNG_READ_ONCE(src[count]);
 160                 if (!c)
 161                         break;
 162                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 163         }
 164         return count;
 165 }
 166
 167 /*
 168  * Copy up to @len string bytes from @src to @dest. Stop whenever a NULL
 169  * terminating character is found in @src, or when a fault occurs.
 170  * Returns the number of bytes copied. Does *not* terminate @dest with
 171  * NULL terminating character.
 172  *
 173  * This function deals with userspace pointers, it should never be called
 174  * directly without having the src pointer checked with access_ok()
 175  * previously.
 176  */
 177 static inline __attribute__((always_inline))
 178 size_t lib_ring_buffer_do_strcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 179                 char *dest, const char __user *src, size_t len)
 180 {
 181         size_t count;
 182
 183         for (count = 0; count < len; count++) {
 184                 int ret;
 185                 char c;
 186
 187                 ret = __copy_from_user_inatomic(&c, src + count, 1);
 188                 if (ret || !c)
 189                         break;
 190                 lib_ring_buffer_do_copy(config, &dest[count], &c, 1);
 191         }
 192         return count;
 193 }
 194
 195 /**
 196  * lib_ring_buffer_strcpy - write string data to a buffer backend
 197  * @config : ring buffer instance configuration
 198  * @ctx: ring buffer context. (input arguments only)
 199  * @src : source pointer to copy from
 200  * @len : length of data to copy
 201  * @pad : character to use for padding
 202  *
 203  * This function copies @len - 1 bytes of string data from a source
 204  * pointer to a buffer backend, followed by a terminating '\0'
 205  * character, at the current context offset. This is more or less a
 206  * buffer backend-specific strncpy() operation. If a terminating '\0'
 207  * character is found in @src before @len - 1 characters are copied, pad
 208  * the buffer with @pad characters (e.g. '#'). Calls the slow path
 209  * (_ring_buffer_strcpy) if copy is crossing a page boundary.
 210  */
 211 static inline
 212 void lib_ring_buffer_strcpy(const struct lttng_kernel_ring_buffer_config *config,
 213                            struct lttng_kernel_ring_buffer_ctx *ctx,
 214                            const char *src, size_t len, int pad)
 215 {
 216         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 217         struct channel_backend *chanb = &ctx->priv.chan->backend;
 218         size_t index, bytes_left_in_page;
 219         size_t offset = ctx->priv.buf_offset;
 220         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 221
 222         if (unlikely(!len))
 223                 return;
 224         backend_pages =
 225                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 226         offset &= chanb->buf_size - 1;
 227         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 228         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 229         if (likely(bytes_left_in_page == len)) {
 230                 size_t count;
 231
 232                 count = lib_ring_buffer_do_strcpy(config,
 233                                         backend_pages->p[index].virt
 234                                             + (offset & ~PAGE_MASK),
 235                                         src, len - 1);
 236                 offset += count;
 237                 /* Padding */
 238                 if (unlikely(count < len - 1)) {
 239                         size_t pad_len = len - 1 - count;
 240
 241                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 242                                                 + (offset & ~PAGE_MASK),
 243                                         pad, pad_len);
 244                         offset += pad_len;
 245                 }
 246                 /* Ending '\0' */
 247                 lib_ring_buffer_do_memset(backend_pages->p[index].virt
 248                                         + (offset & ~PAGE_MASK),
 249                                 '\0', 1);
 250         } else {
 251                 _lib_ring_buffer_strcpy(bufb, offset, src, len, pad);
 252         }
 253         ctx->priv.buf_offset += len;
 254 }
 255
 256 /**
 257  * lib_ring_buffer_pstrcpy - write kernel C-string (input) to a buffer backend P-string
 258  * @config : ring buffer instance configuration
 259  * @ctx: ring buffer context. (input arguments only)
 260  * @src : source pointer to copy from
 261  * @len : length of data to copy
 262  * @pad : character to use for padding
 263  *
 264  * This function copies up to @len bytes of data from a source pointer
 265  * to a Pascal String into the buffer backend. If a terminating '\0'
 266  * character is found in @src before @len characters are copied, pad the
 267  * buffer with @pad characters (e.g. '\0').
 268  *
 269  * The length of the pascal strings in the ring buffer is explicit: it
 270  * is either the array or sequence length.
 271  */
 272 static inline
 273 void lib_ring_buffer_pstrcpy(const struct lttng_kernel_ring_buffer_config *config,
 274                            struct lttng_kernel_ring_buffer_ctx *ctx,
 275                            const char *src, size_t len, char pad)
 276         __attribute__((always_inline));
 277 static inline
 278 void lib_ring_buffer_pstrcpy(const struct lttng_kernel_ring_buffer_config *config,
 279                            struct lttng_kernel_ring_buffer_ctx *ctx,
 280                            const char *src, size_t len, char pad)
 281 {
 282         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 283         struct channel_backend *chanb = &ctx->priv.chan->backend;
 284         size_t index, bytes_left_in_page;
 285         size_t offset = ctx->priv.buf_offset;
 286         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 287
 288         if (unlikely(!len))
 289                 return;
 290         backend_pages =
 291                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 292         offset &= chanb->buf_size - 1;
 293         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 294         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 295         if (likely(bytes_left_in_page == len)) {
 296                 size_t count;
 297
 298                 count = lib_ring_buffer_do_strcpy(config,
 299                                         backend_pages->p[index].virt
 300                                             + (offset & ~PAGE_MASK),
 301                                         src, len);
 302                 offset += count;
 303                 /* Padding */
 304                 if (unlikely(count < len)) {
 305                         size_t pad_len = len - count;
 306
 307                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 308                                                 + (offset & ~PAGE_MASK),
 309                                         pad, pad_len);
 310                         offset += pad_len;
 311                 }
 312         } else {
 313                 _lib_ring_buffer_pstrcpy(bufb, offset, src, len, pad);
 314         }
 315         ctx->priv.buf_offset += len;
 316 }
 317
 318 /**
 319  * lib_ring_buffer_copy_from_user_inatomic - write userspace data to a buffer backend
 320  * @config : ring buffer instance configuration
 321  * @ctx: ring buffer context. (input arguments only)
 322  * @src : userspace source pointer to copy from
 323  * @len : length of data to copy
 324  *
 325  * This function copies "len" bytes of data from a userspace pointer to a
 326  * buffer backend, at the current context offset. This is more or less a buffer
 327  * backend-specific memcpy() operation. Calls the slow path
 328  * (_ring_buffer_write_from_user_inatomic) if copy is crossing a page boundary.
 329  * Disable the page fault handler to ensure we never try to take the mmap_sem.
 330  */
 331 static inline __attribute__((always_inline))
 332 void lib_ring_buffer_copy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 333                                     struct lttng_kernel_ring_buffer_ctx *ctx,
 334                                     const void __user *src, size_t len)
 335 {
 336         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 337         struct channel_backend *chanb = &ctx->priv.chan->backend;
 338         size_t index, pagecpy;
 339         size_t offset = ctx->priv.buf_offset;
 340         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 341         unsigned long ret;
 342
 343         if (unlikely(!len))
 344                 return;
 345         backend_pages =
 346                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 347         offset &= chanb->buf_size - 1;
 348         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 349         pagecpy = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 350
 351         if (unlikely(!lttng_access_ok(VERIFY_READ, src, len)))
 352                 goto fill_buffer;
 353
 354         pagefault_disable();
 355         if (likely(pagecpy == len)) {
 356                 ret = lib_ring_buffer_do_copy_from_user_inatomic(
 357                         backend_pages->p[index].virt + (offset & ~PAGE_MASK),
 358                         src, len);
 359                 if (unlikely(ret > 0)) {
 360                         /* Copy failed. */
 361                         goto fill_buffer_enable_pf;
 362                 }
 363         } else {
 364                 _lib_ring_buffer_copy_from_user_inatomic(bufb, offset, src, len, 0);
 365         }
 366         pagefault_enable();
 367         ctx->priv.buf_offset += len;
 368
 369         return;
 370
 371 fill_buffer_enable_pf:
 372         pagefault_enable();
 373 fill_buffer:
 374         /*
 375          * In the error path we call the slow path version to avoid
 376          * the pollution of static inline code.
 377          */
 378         _lib_ring_buffer_memset(bufb, offset, 0, len, 0);
 379         ctx->priv.buf_offset += len;
 380 }
 381
 382 /**
 383  * lib_ring_buffer_strcpy_from_user_inatomic - write userspace string data to a buffer backend
 384  * @config : ring buffer instance configuration
 385  * @ctx: ring buffer context (input arguments only)
 386  * @src : userspace source pointer to copy from
 387  * @len : length of data to copy
 388  * @pad : character to use for padding
 389  *
 390  * This function copies @len - 1 bytes of string data from a userspace
 391  * source pointer to a buffer backend, followed by a terminating '\0'
 392  * character, at the current context offset. This is more or less a
 393  * buffer backend-specific strncpy() operation. If a terminating '\0'
 394  * character is found in @src before @len - 1 characters are copied, pad
 395  * the buffer with @pad characters (e.g. '#'). Calls the slow path
 396  * (_ring_buffer_strcpy_from_user_inatomic) if copy is crossing a page
 397  * boundary. Disable the page fault handler to ensure we never try to
 398  * take the mmap_sem.
 399  */
 400 static inline
 401 void lib_ring_buffer_strcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 402                 struct lttng_kernel_ring_buffer_ctx *ctx,
 403                 const void __user *src, size_t len, int pad)
 404 {
 405         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 406         struct channel_backend *chanb = &ctx->priv.chan->backend;
 407         size_t index, bytes_left_in_page;
 408         size_t offset = ctx->priv.buf_offset;
 409         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 410
 411         if (unlikely(!len))
 412                 return;
 413         backend_pages =
 414                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 415         offset &= chanb->buf_size - 1;
 416         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 417         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 418
 419         if (unlikely(!lttng_access_ok(VERIFY_READ, src, len)))
 420                 goto fill_buffer;
 421
 422         pagefault_disable();
 423         if (likely(bytes_left_in_page == len)) {
 424                 size_t count;
 425
 426                 count = lib_ring_buffer_do_strcpy_from_user_inatomic(config,
 427                                         backend_pages->p[index].virt
 428                                             + (offset & ~PAGE_MASK),
 429                                         src, len - 1);
 430                 offset += count;
 431                 /* Padding */
 432                 if (unlikely(count < len - 1)) {
 433                         size_t pad_len = len - 1 - count;
 434
 435                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 436                                                 + (offset & ~PAGE_MASK),
 437                                         pad, pad_len);
 438                         offset += pad_len;
 439                 }
 440                 /* Ending '\0' */
 441                 lib_ring_buffer_do_memset(backend_pages->p[index].virt
 442                                         + (offset & ~PAGE_MASK),
 443                                 '\0', 1);
 444         } else {
 445                 _lib_ring_buffer_strcpy_from_user_inatomic(bufb, offset, src,
 446                                         len, pad);
 447         }
 448         pagefault_enable();
 449         ctx->priv.buf_offset += len;
 450
 451         return;
 452
 453 fill_buffer:
 454         /*
 455          * In the error path we call the slow path version to avoid
 456          * the pollution of static inline code.
 457          */
 458         _lib_ring_buffer_memset(bufb, offset, pad, len - 1, 0);
 459         offset += len - 1;
 460         _lib_ring_buffer_memset(bufb, offset, '\0', 1, 0);
 461         ctx->priv.buf_offset += len;
 462 }
 463
 464 /**
 465  * lib_ring_buffer_pstrcpy_from_user_inatomic - write user-space C-string (input) to a buffer backend P-string
 466  * @config : ring buffer instance configuration
 467  * @ctx: ring buffer context. (input arguments only)
 468  * @src : source pointer to copy from
 469  * @len : length of data to copy
 470  * @pad : character to use for padding
 471  *
 472  * This function copies up to @len bytes of data from a source pointer
 473  * to a Pascal String into the buffer backend. If a terminating '\0'
 474  * character is found in @src before @len characters are copied, pad the
 475  * buffer with @pad characters (e.g. '\0').
 476  *
 477  * The length of the pascal strings in the ring buffer is explicit: it
 478  * is either the array or sequence length.
 479  */
 480 static inline
 481 void lib_ring_buffer_pstrcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 482                            struct lttng_kernel_ring_buffer_ctx *ctx,
 483                            const char __user *src, size_t len, char pad)
 484         __attribute__((always_inline));
 485 static inline
 486 void lib_ring_buffer_pstrcpy_from_user_inatomic(const struct lttng_kernel_ring_buffer_config *config,
 487                            struct lttng_kernel_ring_buffer_ctx *ctx,
 488                            const char __user *src, size_t len, char pad)
 489 {
 490         struct lttng_kernel_ring_buffer_backend *bufb = &ctx->priv.buf->backend;
 491         struct channel_backend *chanb = &ctx->priv.chan->backend;
 492         size_t index, bytes_left_in_page;
 493         size_t offset = ctx->priv.buf_offset;
 494         struct lttng_kernel_ring_buffer_backend_pages *backend_pages;
 495
 496         if (unlikely(!len))
 497                 return;
 498         backend_pages =
 499                 lib_ring_buffer_get_backend_pages_from_ctx(config, ctx);
 500         offset &= chanb->buf_size - 1;
 501         index = (offset & (chanb->subbuf_size - 1)) >> PAGE_SHIFT;
 502         bytes_left_in_page = min_t(size_t, len, (-offset) & ~PAGE_MASK);
 503
 504         if (unlikely(!lttng_access_ok(VERIFY_READ, src, len)))
 505                 goto fill_buffer;
 506
 507         pagefault_disable();
 508         if (likely(bytes_left_in_page == len)) {
 509                 size_t count;
 510
 511                 count = lib_ring_buffer_do_strcpy_from_user_inatomic(config,
 512                                         backend_pages->p[index].virt
 513                                             + (offset & ~PAGE_MASK),
 514                                         src, len);
 515                 offset += count;
 516                 /* Padding */
 517                 if (unlikely(count < len)) {
 518                         size_t pad_len = len - count;
 519
 520                         lib_ring_buffer_do_memset(backend_pages->p[index].virt
 521                                                 + (offset & ~PAGE_MASK),
 522                                         pad, pad_len);
 523                         offset += pad_len;
 524                 }
 525         } else {
 526                 _lib_ring_buffer_pstrcpy_from_user_inatomic(bufb, offset, src, len, pad);
 527         }
 528         ctx->priv.buf_offset += len;
 529         pagefault_enable();
 530
 531         return;
 532
 533 fill_buffer:
 534         /*
 535          * In the error path we call the slow path version to avoid
 536          * the pollution of static inline code.
 537          */
 538         _lib_ring_buffer_memset(bufb, offset, pad, len, 0);
 539         ctx->priv.buf_offset += len;
 540 }
 541
 542 /*
 543  * This accessor counts the number of unread records in a buffer.
 544  * It only provides a consistent value if no reads not writes are performed
 545  * concurrently.
 546  */
 547 static inline
 548 unsigned long lib_ring_buffer_get_records_unread(
 549                                 const struct lttng_kernel_ring_buffer_config *config,
 550                                 struct lttng_kernel_ring_buffer *buf)
 551 {
 552         struct lttng_kernel_ring_buffer_backend *bufb = &buf->backend;
 553         struct lttng_kernel_ring_buffer_backend_pages *pages;
 554         unsigned long records_unread = 0, sb_bindex, id;
 555         unsigned int i;
 556
 557         for (i = 0; i < bufb->chan->backend.num_subbuf; i++) {
 558                 id = bufb->buf_wsb[i].id;
 559                 sb_bindex = subbuffer_id_get_index(config, id);
 560                 pages = bufb->array[sb_bindex];
 561                 records_unread += v_read(config, &pages->records_unread);
 562         }
 563         if (config->mode == RING_BUFFER_OVERWRITE) {
 564                 id = bufb->buf_rsb.id;
 565                 sb_bindex = subbuffer_id_get_index(config, id);
 566                 pages = bufb->array[sb_bindex];
 567                 records_unread += v_read(config, &pages->records_unread);
 568         }
 569         return records_unread;
 570 }
 571
 572 /*
 573  * We use __copy_from_user_inatomic to copy userspace data after
 574  * checking with access_ok() and disabling page faults.
 575  *
 576  * Return 0 if OK, nonzero on error.
 577  */
 578 static inline
 579 unsigned long lib_ring_buffer_copy_from_user_check_nofault(void *dest,
 580                                                 const void __user *src,
 581                                                 unsigned long len)
 582 {
 583         unsigned long ret;
 584
 585         if (!lttng_access_ok(VERIFY_READ, src, len))
 586                 return 1;
 587         pagefault_disable();
 588         ret = __copy_from_user_inatomic(dest, src, len);
 589         pagefault_enable();
 590         return ret;
 591 }
 592
 593 #endif /* _LIB_RING_BUFFER_BACKEND_H */