| 1 | /* |
| 2 | * Tty buffer allocation management |
| 3 | */ |
| 4 | |
| 5 | #include <linux/types.h> |
| 6 | #include <linux/errno.h> |
| 7 | #include <linux/tty.h> |
| 8 | #include <linux/tty_driver.h> |
| 9 | #include <linux/tty_flip.h> |
| 10 | #include <linux/timer.h> |
| 11 | #include <linux/string.h> |
| 12 | #include <linux/slab.h> |
| 13 | #include <linux/sched.h> |
| 14 | #include <linux/wait.h> |
| 15 | #include <linux/bitops.h> |
| 16 | #include <linux/delay.h> |
| 17 | #include <linux/module.h> |
| 18 | #include <linux/ratelimit.h> |
| 19 | |
| 20 | |
| 21 | #define MIN_TTYB_SIZE 256 |
| 22 | #define TTYB_ALIGN_MASK 255 |
| 23 | |
| 24 | /* |
| 25 | * Byte threshold to limit memory consumption for flip buffers. |
| 26 | * The actual memory limit is > 2x this amount. |
| 27 | */ |
| 28 | #define TTYB_DEFAULT_MEM_LIMIT 65536 |
| 29 | |
| 30 | /* |
| 31 | * We default to dicing tty buffer allocations to this many characters |
| 32 | * in order to avoid multiple page allocations. We know the size of |
| 33 | * tty_buffer itself but it must also be taken into account that the |
| 34 | * the buffer is 256 byte aligned. See tty_buffer_find for the allocation |
| 35 | * logic this must match |
| 36 | */ |
| 37 | |
| 38 | #define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF) |
| 39 | |
| 40 | |
| 41 | /** |
| 42 | * tty_buffer_lock_exclusive - gain exclusive access to buffer |
| 43 | * tty_buffer_unlock_exclusive - release exclusive access |
| 44 | * |
| 45 | * @port - tty_port owning the flip buffer |
| 46 | * |
| 47 | * Guarantees safe use of the line discipline's receive_buf() method by |
| 48 | * excluding the buffer work and any pending flush from using the flip |
| 49 | * buffer. Data can continue to be added concurrently to the flip buffer |
| 50 | * from the driver side. |
| 51 | * |
| 52 | * On release, the buffer work is restarted if there is data in the |
| 53 | * flip buffer |
| 54 | */ |
| 55 | |
| 56 | void tty_buffer_lock_exclusive(struct tty_port *port) |
| 57 | { |
| 58 | struct tty_bufhead *buf = &port->buf; |
| 59 | |
| 60 | atomic_inc(&buf->priority); |
| 61 | mutex_lock(&buf->lock); |
| 62 | } |
| 63 | |
| 64 | void tty_buffer_unlock_exclusive(struct tty_port *port) |
| 65 | { |
| 66 | struct tty_bufhead *buf = &port->buf; |
| 67 | int restart; |
| 68 | |
| 69 | restart = buf->head->commit != buf->head->read; |
| 70 | |
| 71 | atomic_dec(&buf->priority); |
| 72 | mutex_unlock(&buf->lock); |
| 73 | if (restart) |
| 74 | queue_work(system_unbound_wq, &buf->work); |
| 75 | } |
| 76 | |
| 77 | /** |
| 78 | * tty_buffer_space_avail - return unused buffer space |
| 79 | * @port - tty_port owning the flip buffer |
| 80 | * |
| 81 | * Returns the # of bytes which can be written by the driver without |
| 82 | * reaching the buffer limit. |
| 83 | * |
| 84 | * Note: this does not guarantee that memory is available to write |
| 85 | * the returned # of bytes (use tty_prepare_flip_string_xxx() to |
| 86 | * pre-allocate if memory guarantee is required). |
| 87 | */ |
| 88 | |
| 89 | int tty_buffer_space_avail(struct tty_port *port) |
| 90 | { |
| 91 | int space = port->buf.mem_limit - atomic_read(&port->buf.mem_used); |
| 92 | return max(space, 0); |
| 93 | } |
| 94 | EXPORT_SYMBOL_GPL(tty_buffer_space_avail); |
| 95 | |
| 96 | static void tty_buffer_reset(struct tty_buffer *p, size_t size) |
| 97 | { |
| 98 | p->used = 0; |
| 99 | p->size = size; |
| 100 | p->next = NULL; |
| 101 | p->commit = 0; |
| 102 | p->read = 0; |
| 103 | p->flags = 0; |
| 104 | } |
| 105 | |
| 106 | /** |
| 107 | * tty_buffer_free_all - free buffers used by a tty |
| 108 | * @tty: tty to free from |
| 109 | * |
| 110 | * Remove all the buffers pending on a tty whether queued with data |
| 111 | * or in the free ring. Must be called when the tty is no longer in use |
| 112 | */ |
| 113 | |
| 114 | void tty_buffer_free_all(struct tty_port *port) |
| 115 | { |
| 116 | struct tty_bufhead *buf = &port->buf; |
| 117 | struct tty_buffer *p, *next; |
| 118 | struct llist_node *llist; |
| 119 | |
| 120 | while ((p = buf->head) != NULL) { |
| 121 | buf->head = p->next; |
| 122 | if (p->size > 0) |
| 123 | kfree(p); |
| 124 | } |
| 125 | llist = llist_del_all(&buf->free); |
| 126 | llist_for_each_entry_safe(p, next, llist, free) |
| 127 | kfree(p); |
| 128 | |
| 129 | tty_buffer_reset(&buf->sentinel, 0); |
| 130 | buf->head = &buf->sentinel; |
| 131 | buf->tail = &buf->sentinel; |
| 132 | |
| 133 | atomic_set(&buf->mem_used, 0); |
| 134 | } |
| 135 | |
| 136 | /** |
| 137 | * tty_buffer_alloc - allocate a tty buffer |
| 138 | * @tty: tty device |
| 139 | * @size: desired size (characters) |
| 140 | * |
| 141 | * Allocate a new tty buffer to hold the desired number of characters. |
| 142 | * We round our buffers off in 256 character chunks to get better |
| 143 | * allocation behaviour. |
| 144 | * Return NULL if out of memory or the allocation would exceed the |
| 145 | * per device queue |
| 146 | */ |
| 147 | |
| 148 | static struct tty_buffer *tty_buffer_alloc(struct tty_port *port, size_t size) |
| 149 | { |
| 150 | struct llist_node *free; |
| 151 | struct tty_buffer *p; |
| 152 | |
| 153 | /* Round the buffer size out */ |
| 154 | size = __ALIGN_MASK(size, TTYB_ALIGN_MASK); |
| 155 | |
| 156 | if (size <= MIN_TTYB_SIZE) { |
| 157 | free = llist_del_first(&port->buf.free); |
| 158 | if (free) { |
| 159 | p = llist_entry(free, struct tty_buffer, free); |
| 160 | goto found; |
| 161 | } |
| 162 | } |
| 163 | |
| 164 | /* Should possibly check if this fails for the largest buffer we |
| 165 | have queued and recycle that ? */ |
| 166 | if (atomic_read(&port->buf.mem_used) > port->buf.mem_limit) |
| 167 | return NULL; |
| 168 | p = kmalloc(sizeof(struct tty_buffer) + 2 * size, GFP_ATOMIC); |
| 169 | if (p == NULL) |
| 170 | return NULL; |
| 171 | |
| 172 | found: |
| 173 | tty_buffer_reset(p, size); |
| 174 | atomic_add(size, &port->buf.mem_used); |
| 175 | return p; |
| 176 | } |
| 177 | |
| 178 | /** |
| 179 | * tty_buffer_free - free a tty buffer |
| 180 | * @tty: tty owning the buffer |
| 181 | * @b: the buffer to free |
| 182 | * |
| 183 | * Free a tty buffer, or add it to the free list according to our |
| 184 | * internal strategy |
| 185 | */ |
| 186 | |
| 187 | static void tty_buffer_free(struct tty_port *port, struct tty_buffer *b) |
| 188 | { |
| 189 | struct tty_bufhead *buf = &port->buf; |
| 190 | |
| 191 | /* Dumb strategy for now - should keep some stats */ |
| 192 | WARN_ON(atomic_sub_return(b->size, &buf->mem_used) < 0); |
| 193 | |
| 194 | if (b->size > MIN_TTYB_SIZE) |
| 195 | kfree(b); |
| 196 | else if (b->size > 0) |
| 197 | llist_add(&b->free, &buf->free); |
| 198 | } |
| 199 | |
| 200 | /** |
| 201 | * tty_buffer_flush - flush full tty buffers |
| 202 | * @tty: tty to flush |
| 203 | * |
| 204 | * flush all the buffers containing receive data. |
| 205 | * |
| 206 | * Locking: takes buffer lock to ensure single-threaded flip buffer |
| 207 | * 'consumer' |
| 208 | */ |
| 209 | |
| 210 | void tty_buffer_flush(struct tty_struct *tty) |
| 211 | { |
| 212 | struct tty_port *port = tty->port; |
| 213 | struct tty_bufhead *buf = &port->buf; |
| 214 | struct tty_buffer *next; |
| 215 | |
| 216 | atomic_inc(&buf->priority); |
| 217 | |
| 218 | mutex_lock(&buf->lock); |
| 219 | while ((next = buf->head->next) != NULL) { |
| 220 | tty_buffer_free(port, buf->head); |
| 221 | buf->head = next; |
| 222 | } |
| 223 | buf->head->read = buf->head->commit; |
| 224 | atomic_dec(&buf->priority); |
| 225 | mutex_unlock(&buf->lock); |
| 226 | } |
| 227 | |
| 228 | /** |
| 229 | * tty_buffer_request_room - grow tty buffer if needed |
| 230 | * @tty: tty structure |
| 231 | * @size: size desired |
| 232 | * @flags: buffer flags if new buffer allocated (default = 0) |
| 233 | * |
| 234 | * Make at least size bytes of linear space available for the tty |
| 235 | * buffer. If we fail return the size we managed to find. |
| 236 | * |
| 237 | * Will change over to a new buffer if the current buffer is encoded as |
| 238 | * TTY_NORMAL (so has no flags buffer) and the new buffer requires |
| 239 | * a flags buffer. |
| 240 | */ |
| 241 | static int __tty_buffer_request_room(struct tty_port *port, size_t size, |
| 242 | int flags) |
| 243 | { |
| 244 | struct tty_bufhead *buf = &port->buf; |
| 245 | struct tty_buffer *b, *n; |
| 246 | int left, change; |
| 247 | |
| 248 | b = buf->tail; |
| 249 | if (b->flags & TTYB_NORMAL) |
| 250 | left = 2 * b->size - b->used; |
| 251 | else |
| 252 | left = b->size - b->used; |
| 253 | |
| 254 | change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL); |
| 255 | if (change || left < size) { |
| 256 | /* This is the slow path - looking for new buffers to use */ |
| 257 | if ((n = tty_buffer_alloc(port, size)) != NULL) { |
| 258 | n->flags = flags; |
| 259 | buf->tail = n; |
| 260 | b->commit = b->used; |
| 261 | smp_mb(); |
| 262 | b->next = n; |
| 263 | } else if (change) |
| 264 | size = 0; |
| 265 | else |
| 266 | size = left; |
| 267 | } |
| 268 | return size; |
| 269 | } |
| 270 | |
| 271 | int tty_buffer_request_room(struct tty_port *port, size_t size) |
| 272 | { |
| 273 | return __tty_buffer_request_room(port, size, 0); |
| 274 | } |
| 275 | EXPORT_SYMBOL_GPL(tty_buffer_request_room); |
| 276 | |
| 277 | /** |
| 278 | * tty_insert_flip_string_fixed_flag - Add characters to the tty buffer |
| 279 | * @port: tty port |
| 280 | * @chars: characters |
| 281 | * @flag: flag value for each character |
| 282 | * @size: size |
| 283 | * |
| 284 | * Queue a series of bytes to the tty buffering. All the characters |
| 285 | * passed are marked with the supplied flag. Returns the number added. |
| 286 | */ |
| 287 | |
| 288 | int tty_insert_flip_string_fixed_flag(struct tty_port *port, |
| 289 | const unsigned char *chars, char flag, size_t size) |
| 290 | { |
| 291 | int copied = 0; |
| 292 | do { |
| 293 | int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); |
| 294 | int flags = (flag == TTY_NORMAL) ? TTYB_NORMAL : 0; |
| 295 | int space = __tty_buffer_request_room(port, goal, flags); |
| 296 | struct tty_buffer *tb = port->buf.tail; |
| 297 | if (unlikely(space == 0)) |
| 298 | break; |
| 299 | memcpy(char_buf_ptr(tb, tb->used), chars, space); |
| 300 | if (~tb->flags & TTYB_NORMAL) |
| 301 | memset(flag_buf_ptr(tb, tb->used), flag, space); |
| 302 | tb->used += space; |
| 303 | copied += space; |
| 304 | chars += space; |
| 305 | /* There is a small chance that we need to split the data over |
| 306 | several buffers. If this is the case we must loop */ |
| 307 | } while (unlikely(size > copied)); |
| 308 | return copied; |
| 309 | } |
| 310 | EXPORT_SYMBOL(tty_insert_flip_string_fixed_flag); |
| 311 | |
| 312 | /** |
| 313 | * tty_insert_flip_string_flags - Add characters to the tty buffer |
| 314 | * @port: tty port |
| 315 | * @chars: characters |
| 316 | * @flags: flag bytes |
| 317 | * @size: size |
| 318 | * |
| 319 | * Queue a series of bytes to the tty buffering. For each character |
| 320 | * the flags array indicates the status of the character. Returns the |
| 321 | * number added. |
| 322 | */ |
| 323 | |
| 324 | int tty_insert_flip_string_flags(struct tty_port *port, |
| 325 | const unsigned char *chars, const char *flags, size_t size) |
| 326 | { |
| 327 | int copied = 0; |
| 328 | do { |
| 329 | int goal = min_t(size_t, size - copied, TTY_BUFFER_PAGE); |
| 330 | int space = tty_buffer_request_room(port, goal); |
| 331 | struct tty_buffer *tb = port->buf.tail; |
| 332 | if (unlikely(space == 0)) |
| 333 | break; |
| 334 | memcpy(char_buf_ptr(tb, tb->used), chars, space); |
| 335 | memcpy(flag_buf_ptr(tb, tb->used), flags, space); |
| 336 | tb->used += space; |
| 337 | copied += space; |
| 338 | chars += space; |
| 339 | flags += space; |
| 340 | /* There is a small chance that we need to split the data over |
| 341 | several buffers. If this is the case we must loop */ |
| 342 | } while (unlikely(size > copied)); |
| 343 | return copied; |
| 344 | } |
| 345 | EXPORT_SYMBOL(tty_insert_flip_string_flags); |
| 346 | |
| 347 | /** |
| 348 | * tty_schedule_flip - push characters to ldisc |
| 349 | * @port: tty port to push from |
| 350 | * |
| 351 | * Takes any pending buffers and transfers their ownership to the |
| 352 | * ldisc side of the queue. It then schedules those characters for |
| 353 | * processing by the line discipline. |
| 354 | * Note that this function can only be used when the low_latency flag |
| 355 | * is unset. Otherwise the workqueue won't be flushed. |
| 356 | */ |
| 357 | |
| 358 | void tty_schedule_flip(struct tty_port *port) |
| 359 | { |
| 360 | struct tty_bufhead *buf = &port->buf; |
| 361 | WARN_ON(port->low_latency); |
| 362 | |
| 363 | buf->tail->commit = buf->tail->used; |
| 364 | schedule_work(&buf->work); |
| 365 | } |
| 366 | EXPORT_SYMBOL(tty_schedule_flip); |
| 367 | |
| 368 | /** |
| 369 | * tty_prepare_flip_string - make room for characters |
| 370 | * @port: tty port |
| 371 | * @chars: return pointer for character write area |
| 372 | * @size: desired size |
| 373 | * |
| 374 | * Prepare a block of space in the buffer for data. Returns the length |
| 375 | * available and buffer pointer to the space which is now allocated and |
| 376 | * accounted for as ready for normal characters. This is used for drivers |
| 377 | * that need their own block copy routines into the buffer. There is no |
| 378 | * guarantee the buffer is a DMA target! |
| 379 | */ |
| 380 | |
| 381 | int tty_prepare_flip_string(struct tty_port *port, unsigned char **chars, |
| 382 | size_t size) |
| 383 | { |
| 384 | int space = __tty_buffer_request_room(port, size, TTYB_NORMAL); |
| 385 | if (likely(space)) { |
| 386 | struct tty_buffer *tb = port->buf.tail; |
| 387 | *chars = char_buf_ptr(tb, tb->used); |
| 388 | if (~tb->flags & TTYB_NORMAL) |
| 389 | memset(flag_buf_ptr(tb, tb->used), TTY_NORMAL, space); |
| 390 | tb->used += space; |
| 391 | } |
| 392 | return space; |
| 393 | } |
| 394 | EXPORT_SYMBOL_GPL(tty_prepare_flip_string); |
| 395 | |
| 396 | |
| 397 | static int |
| 398 | receive_buf(struct tty_struct *tty, struct tty_buffer *head, int count) |
| 399 | { |
| 400 | struct tty_ldisc *disc = tty->ldisc; |
| 401 | unsigned char *p = char_buf_ptr(head, head->read); |
| 402 | char *f = NULL; |
| 403 | |
| 404 | if (~head->flags & TTYB_NORMAL) |
| 405 | f = flag_buf_ptr(head, head->read); |
| 406 | |
| 407 | if (disc->ops->receive_buf2) |
| 408 | count = disc->ops->receive_buf2(tty, p, f, count); |
| 409 | else { |
| 410 | count = min_t(int, count, tty->receive_room); |
| 411 | if (count) |
| 412 | disc->ops->receive_buf(tty, p, f, count); |
| 413 | } |
| 414 | head->read += count; |
| 415 | return count; |
| 416 | } |
| 417 | |
| 418 | /** |
| 419 | * flush_to_ldisc |
| 420 | * @work: tty structure passed from work queue. |
| 421 | * |
| 422 | * This routine is called out of the software interrupt to flush data |
| 423 | * from the buffer chain to the line discipline. |
| 424 | * |
| 425 | * The receive_buf method is single threaded for each tty instance. |
| 426 | * |
| 427 | * Locking: takes buffer lock to ensure single-threaded flip buffer |
| 428 | * 'consumer' |
| 429 | */ |
| 430 | |
| 431 | static void flush_to_ldisc(struct work_struct *work) |
| 432 | { |
| 433 | struct tty_port *port = container_of(work, struct tty_port, buf.work); |
| 434 | struct tty_bufhead *buf = &port->buf; |
| 435 | struct tty_struct *tty; |
| 436 | struct tty_ldisc *disc; |
| 437 | |
| 438 | tty = port->itty; |
| 439 | if (tty == NULL) |
| 440 | return; |
| 441 | |
| 442 | disc = tty_ldisc_ref(tty); |
| 443 | if (disc == NULL) |
| 444 | return; |
| 445 | |
| 446 | mutex_lock(&buf->lock); |
| 447 | |
| 448 | while (1) { |
| 449 | struct tty_buffer *head = buf->head; |
| 450 | int count; |
| 451 | |
| 452 | /* Ldisc or user is trying to gain exclusive access */ |
| 453 | if (atomic_read(&buf->priority)) |
| 454 | break; |
| 455 | |
| 456 | count = head->commit - head->read; |
| 457 | if (!count) { |
| 458 | if (head->next == NULL) |
| 459 | break; |
| 460 | buf->head = head->next; |
| 461 | tty_buffer_free(port, head); |
| 462 | continue; |
| 463 | } |
| 464 | |
| 465 | count = receive_buf(tty, head, count); |
| 466 | if (!count) |
| 467 | break; |
| 468 | } |
| 469 | |
| 470 | mutex_unlock(&buf->lock); |
| 471 | |
| 472 | tty_ldisc_deref(disc); |
| 473 | } |
| 474 | |
| 475 | /** |
| 476 | * tty_flush_to_ldisc |
| 477 | * @tty: tty to push |
| 478 | * |
| 479 | * Push the terminal flip buffers to the line discipline. |
| 480 | * |
| 481 | * Must not be called from IRQ context. |
| 482 | */ |
| 483 | void tty_flush_to_ldisc(struct tty_struct *tty) |
| 484 | { |
| 485 | if (!tty->port->low_latency) |
| 486 | flush_work(&tty->port->buf.work); |
| 487 | } |
| 488 | |
| 489 | /** |
| 490 | * tty_flip_buffer_push - terminal |
| 491 | * @port: tty port to push |
| 492 | * |
| 493 | * Queue a push of the terminal flip buffers to the line discipline. This |
| 494 | * function must not be called from IRQ context if port->low_latency is |
| 495 | * set. |
| 496 | * |
| 497 | * In the event of the queue being busy for flipping the work will be |
| 498 | * held off and retried later. |
| 499 | */ |
| 500 | |
| 501 | void tty_flip_buffer_push(struct tty_port *port) |
| 502 | { |
| 503 | struct tty_bufhead *buf = &port->buf; |
| 504 | |
| 505 | buf->tail->commit = buf->tail->used; |
| 506 | |
| 507 | if (port->low_latency) |
| 508 | flush_to_ldisc(&buf->work); |
| 509 | else |
| 510 | schedule_work(&buf->work); |
| 511 | } |
| 512 | EXPORT_SYMBOL(tty_flip_buffer_push); |
| 513 | |
| 514 | /** |
| 515 | * tty_buffer_init - prepare a tty buffer structure |
| 516 | * @tty: tty to initialise |
| 517 | * |
| 518 | * Set up the initial state of the buffer management for a tty device. |
| 519 | * Must be called before the other tty buffer functions are used. |
| 520 | */ |
| 521 | |
| 522 | void tty_buffer_init(struct tty_port *port) |
| 523 | { |
| 524 | struct tty_bufhead *buf = &port->buf; |
| 525 | |
| 526 | mutex_init(&buf->lock); |
| 527 | tty_buffer_reset(&buf->sentinel, 0); |
| 528 | buf->head = &buf->sentinel; |
| 529 | buf->tail = &buf->sentinel; |
| 530 | init_llist_head(&buf->free); |
| 531 | atomic_set(&buf->mem_used, 0); |
| 532 | atomic_set(&buf->priority, 0); |
| 533 | INIT_WORK(&buf->work, flush_to_ldisc); |
| 534 | buf->mem_limit = TTYB_DEFAULT_MEM_LIMIT; |
| 535 | } |
| 536 | |
| 537 | /** |
| 538 | * tty_buffer_set_limit - change the tty buffer memory limit |
| 539 | * @port: tty port to change |
| 540 | * |
| 541 | * Change the tty buffer memory limit. |
| 542 | * Must be called before the other tty buffer functions are used. |
| 543 | */ |
| 544 | |
| 545 | int tty_buffer_set_limit(struct tty_port *port, int limit) |
| 546 | { |
| 547 | if (limit < MIN_TTYB_SIZE) |
| 548 | return -EINVAL; |
| 549 | port->buf.mem_limit = limit; |
| 550 | return 0; |
| 551 | } |
| 552 | EXPORT_SYMBOL_GPL(tty_buffer_set_limit); |