sys/kern/tty_outq.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause
   3  *
   4  * Copyright (c) 2008 Ed Schouten <ed@FreeBSD.org>
   5  * All rights reserved.
   6  *
   7  * Portions of this software were developed under sponsorship from Snow
   8  * B.V., the Netherlands.
   9  *
  10  * Redistribution and use in source and binary forms, with or without
  11  * modification, are permitted provided that the following conditions
  12  * are met:
  13  * 1. Redistributions of source code must retain the above copyright
  14  *    notice, this list of conditions and the following disclaimer.
  15  * 2. Redistributions in binary form must reproduce the above copyright
  16  *    notice, this list of conditions and the following disclaimer in the
  17  *    documentation and/or other materials provided with the distribution.
  18  *
  19  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  20  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  23  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29  * SUCH DAMAGE.
  30  */
  31
  32 #include <sys/param.h>
  33 #include <sys/kernel.h>
  34 #include <sys/lock.h>
  35 #include <sys/queue.h>
  36 #include <sys/systm.h>
  37 #include <sys/tty.h>
  38 #include <sys/uio.h>
  39
  40 #include <vm/uma.h>
  41
  42 /*
  43  * TTY output queue buffering.
  44  *
  45  * The previous design of the TTY layer offered the so-called clists.
  46  * These clists were used for both the input queues and the output
  47  * queue. We don't use certain features on the output side, like quoting
  48  * bits for parity marking and such. This mechanism is similar to the
  49  * old clists, but only contains the features we need to buffer the
  50  * output.
  51  */
  52
  53 struct ttyoutq_block {
  54         struct ttyoutq_block    *tob_next;
  55         char                    tob_data[TTYOUTQ_DATASIZE];
  56 };
  57
  58 static uma_zone_t ttyoutq_zone;
  59
  60 #define TTYOUTQ_INSERT_TAIL(to, tob) do {                               \
  61         if (to->to_end == 0) {                                          \
  62                 tob->tob_next = to->to_firstblock;                      \
  63                 to->to_firstblock = tob;                                \
  64         } else {                                                        \
  65                 tob->tob_next = to->to_lastblock->tob_next;             \
  66                 to->to_lastblock->tob_next = tob;                       \
  67         }                                                               \
  68         to->to_nblocks++;                                               \
  69 } while (0)
  70
  71 #define TTYOUTQ_REMOVE_HEAD(to) do {                                    \
  72         to->to_firstblock = to->to_firstblock->tob_next;                \
  73         to->to_nblocks--;                                               \
  74 } while (0)
  75
  76 #define TTYOUTQ_RECYCLE(to, tob) do {                                   \
  77         if (to->to_quota <= to->to_nblocks)                             \
  78                 uma_zfree(ttyoutq_zone, tob);                           \
  79         else                                                            \
  80                 TTYOUTQ_INSERT_TAIL(to, tob);                           \
  81 } while (0)
  82
  83 void
  84 ttyoutq_flush(struct ttyoutq *to)
  85 {
  86
  87         to->to_begin = 0;
  88         to->to_end = 0;
  89 }
  90
  91 int
  92 ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
  93 {
  94         struct ttyoutq_block *tob;
  95
  96         to->to_quota = howmany(size, TTYOUTQ_DATASIZE);
  97
  98         while (to->to_quota > to->to_nblocks) {
  99                 /*
 100                  * List is getting bigger.
 101                  * Add new blocks to the tail of the list.
 102                  *
 103                  * We must unlock the TTY temporarily, because we need
 104                  * to allocate memory. This won't be a problem, because
 105                  * in the worst case, another thread ends up here, which
 106                  * may cause us to allocate too many blocks, but this
 107                  * will be caught by the loop below.
 108                  */
 109                 tty_unlock(tp);
 110                 tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
 111                 tty_lock(tp);
 112
 113                 if (tty_gone(tp)) {
 114                         uma_zfree(ttyoutq_zone, tob);
 115                         return (ENXIO);
 116                 }
 117
 118                 TTYOUTQ_INSERT_TAIL(to, tob);
 119         }
 120         return (0);
 121 }
 122
 123 void
 124 ttyoutq_free(struct ttyoutq *to)
 125 {
 126         struct ttyoutq_block *tob;
 127
 128         ttyoutq_flush(to);
 129         to->to_quota = 0;
 130
 131         while ((tob = to->to_firstblock) != NULL) {
 132                 TTYOUTQ_REMOVE_HEAD(to);
 133                 uma_zfree(ttyoutq_zone, tob);
 134         }
 135
 136         MPASS(to->to_nblocks == 0);
 137 }
 138
 139 size_t
 140 ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
 141 {
 142         char *cbuf = buf;
 143
 144         while (len > 0) {
 145                 struct ttyoutq_block *tob;
 146                 size_t cbegin, cend, clen;
 147
 148                 /* See if there still is data. */
 149                 if (to->to_begin == to->to_end)
 150                         break;
 151                 tob = to->to_firstblock;
 152                 if (tob == NULL)
 153                         break;
 154
 155                 /*
 156                  * The end address should be the lowest of these three:
 157                  * - The write pointer
 158                  * - The blocksize - we can't read beyond the block
 159                  * - The end address if we could perform the full read
 160                  */
 161                 cbegin = to->to_begin;
 162                 cend = MIN(MIN(to->to_end, to->to_begin + len),
 163                     TTYOUTQ_DATASIZE);
 164                 clen = cend - cbegin;
 165
 166                 /* Copy the data out of the buffers. */
 167                 memcpy(cbuf, tob->tob_data + cbegin, clen);
 168                 cbuf += clen;
 169                 len -= clen;
 170
 171                 if (cend == to->to_end) {
 172                         /* Read the complete queue. */
 173                         to->to_begin = 0;
 174                         to->to_end = 0;
 175                 } else if (cend == TTYOUTQ_DATASIZE) {
 176                         /* Read the block until the end. */
 177                         TTYOUTQ_REMOVE_HEAD(to);
 178                         to->to_begin = 0;
 179                         to->to_end -= TTYOUTQ_DATASIZE;
 180                         TTYOUTQ_RECYCLE(to, tob);
 181                 } else {
 182                         /* Read the block partially. */
 183                         to->to_begin += clen;
 184                 }
 185         }
 186
 187         return (cbuf - (char *)buf);
 188 }
 189
 190 /*
 191  * An optimized version of ttyoutq_read() which can be used in pseudo
 192  * TTY drivers to directly copy data from the outq to userspace, instead
 193  * of buffering it.
 194  *
 195  * We can only copy data directly if we need to read the entire block
 196  * back to the user, because we temporarily remove the block from the
 197  * queue. Otherwise we need to copy it to a temporary buffer first, to
 198  * make sure data remains in the correct order.
 199  */
 200 int
 201 ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
 202 {
 203
 204         while (uio->uio_resid > 0) {
 205                 int error;
 206                 struct ttyoutq_block *tob;
 207                 size_t cbegin, cend, clen;
 208
 209                 /* See if there still is data. */
 210                 if (to->to_begin == to->to_end)
 211                         return (0);
 212                 tob = to->to_firstblock;
 213                 if (tob == NULL)
 214                         return (0);
 215
 216                 /*
 217                  * The end address should be the lowest of these three:
 218                  * - The write pointer
 219                  * - The blocksize - we can't read beyond the block
 220                  * - The end address if we could perform the full read
 221                  */
 222                 cbegin = to->to_begin;
 223                 cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
 224                     TTYOUTQ_DATASIZE);
 225                 clen = cend - cbegin;
 226
 227                 /*
 228                  * We can prevent buffering in some cases:
 229                  * - We need to read the block until the end.
 230                  * - We don't need to read the block until the end, but
 231                  *   there is no data beyond it, which allows us to move
 232                  *   the write pointer to a new block.
 233                  */
 234                 if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
 235                         /*
 236                          * Fast path: zero copy. Remove the first block,
 237                          * so we can unlock the TTY temporarily.
 238                          */
 239                         TTYOUTQ_REMOVE_HEAD(to);
 240                         to->to_begin = 0;
 241                         if (to->to_end <= TTYOUTQ_DATASIZE)
 242                                 to->to_end = 0;
 243                         else
 244                                 to->to_end -= TTYOUTQ_DATASIZE;
 245
 246                         /* Temporary unlock and copy the data to userspace. */
 247                         tty_unlock(tp);
 248                         error = uiomove(tob->tob_data + cbegin, clen, uio);
 249                         tty_lock(tp);
 250
 251                         /* Block can now be readded to the list. */
 252                         TTYOUTQ_RECYCLE(to, tob);
 253                 } else {
 254                         char ob[TTYOUTQ_DATASIZE - 1];
 255
 256                         /*
 257                          * Slow path: store data in a temporary buffer.
 258                          */
 259                         memcpy(ob, tob->tob_data + cbegin, clen);
 260                         to->to_begin += clen;
 261                         MPASS(to->to_begin < TTYOUTQ_DATASIZE);
 262
 263                         /* Temporary unlock and copy the data to userspace. */
 264                         tty_unlock(tp);
 265                         error = uiomove(ob, clen, uio);
 266                         tty_lock(tp);
 267                 }
 268
 269                 if (error != 0)
 270                         return (error);
 271         }
 272
 273         return (0);
 274 }
 275
 276 size_t
 277 ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
 278 {
 279         const char *cbuf = buf;
 280         struct ttyoutq_block *tob;
 281         unsigned int boff;
 282         size_t l;
 283
 284         while (nbytes > 0) {
 285                 boff = to->to_end % TTYOUTQ_DATASIZE;
 286
 287                 if (to->to_end == 0) {
 288                         /* First time we're being used or drained. */
 289                         MPASS(to->to_begin == 0);
 290                         tob = to->to_firstblock;
 291                         if (tob == NULL) {
 292                                 /* Queue has no blocks. */
 293                                 break;
 294                         }
 295                         to->to_lastblock = tob;
 296                 } else if (boff == 0) {
 297                         /* We reached the end of this block on last write. */
 298                         tob = to->to_lastblock->tob_next;
 299                         if (tob == NULL) {
 300                                 /* We've reached the watermark. */
 301                                 break;
 302                         }
 303                         to->to_lastblock = tob;
 304                 } else {
 305                         tob = to->to_lastblock;
 306                 }
 307
 308                 /* Don't copy more than was requested. */
 309                 l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
 310                 MPASS(l > 0);
 311                 memcpy(tob->tob_data + boff, cbuf, l);
 312
 313                 cbuf += l;
 314                 nbytes -= l;
 315                 to->to_end += l;
 316         }
 317
 318         return (cbuf - (const char *)buf);
 319 }
 320
 321 int
 322 ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
 323 {
 324         size_t ret __unused;
 325
 326         if (ttyoutq_bytesleft(to) < nbytes)
 327                 return (-1);
 328
 329         /* We should always be able to write it back. */
 330         ret = ttyoutq_write(to, buf, nbytes);
 331         MPASS(ret == nbytes);
 332
 333         return (0);
 334 }
 335
 336 static void
 337 ttyoutq_startup(void *dummy)
 338 {
 339
 340         ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
 341             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
 342 }
 343
 344 SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);