sys/kern/tty_outq.c

   1 /*-
   2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
   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/cdefs.h>
  33 __FBSDID("$FreeBSD$");
  34
  35 #include <sys/param.h>
  36 #include <sys/kernel.h>
  37 #include <sys/lock.h>
  38 #include <sys/queue.h>
  39 #include <sys/systm.h>
  40 #include <sys/tty.h>
  41 #include <sys/uio.h>
  42
  43 #include <vm/uma.h>
  44
  45 /*
  46  * TTY output queue buffering.
  47  *
  48  * The previous design of the TTY layer offered the so-called clists.
  49  * These clists were used for both the input queues and the output
  50  * queue. We don't use certain features on the output side, like quoting
  51  * bits for parity marking and such. This mechanism is similar to the
  52  * old clists, but only contains the features we need to buffer the
  53  * output.
  54  */
  55
  56 struct ttyoutq_block {
  57         struct ttyoutq_block    *tob_next;
  58         char                    tob_data[TTYOUTQ_DATASIZE];
  59 };
  60
  61 static uma_zone_t ttyoutq_zone;
  62
  63 #define TTYOUTQ_INSERT_TAIL(to, tob) do {                               \
  64         if (to->to_end == 0) {                                          \
  65                 tob->tob_next = to->to_firstblock;                      \
  66                 to->to_firstblock = tob;                                \
  67         } else {                                                        \
  68                 tob->tob_next = to->to_lastblock->tob_next;             \
  69                 to->to_lastblock->tob_next = tob;                       \
  70         }                                                               \
  71         to->to_nblocks++;                                               \
  72 } while (0)
  73
  74 #define TTYOUTQ_REMOVE_HEAD(to) do {                                    \
  75         to->to_firstblock = to->to_firstblock->tob_next;                \
  76         to->to_nblocks--;                                               \
  77 } while (0)
  78
  79 #define TTYOUTQ_RECYCLE(to, tob) do {                                   \
  80         if (to->to_quota <= to->to_nblocks)                             \
  81                 uma_zfree(ttyoutq_zone, tob);                           \
  82         else                                                            \
  83                 TTYOUTQ_INSERT_TAIL(to, tob);                           \
  84 } while(0)
  85
  86 void
  87 ttyoutq_flush(struct ttyoutq *to)
  88 {
  89
  90         to->to_begin = 0;
  91         to->to_end = 0;
  92 }
  93
  94 int
  95 ttyoutq_setsize(struct ttyoutq *to, struct tty *tp, size_t size)
  96 {
  97         struct ttyoutq_block *tob;
  98
  99         to->to_quota = howmany(size, TTYOUTQ_DATASIZE);
 100
 101         while (to->to_quota > to->to_nblocks) {
 102                 /*
 103                  * List is getting bigger.
 104                  * Add new blocks to the tail of the list.
 105                  *
 106                  * We must unlock the TTY temporarily, because we need
 107                  * to allocate memory. This won't be a problem, because
 108                  * in the worst case, another thread ends up here, which
 109                  * may cause us to allocate too many blocks, but this
 110                  * will be caught by the loop below.
 111                  */
 112                 tty_unlock(tp);
 113                 tob = uma_zalloc(ttyoutq_zone, M_WAITOK);
 114                 tty_lock(tp);
 115
 116                 if (tty_gone(tp)) {
 117                         uma_zfree(ttyoutq_zone, tob);
 118                         return (ENXIO);
 119                 }
 120
 121                 TTYOUTQ_INSERT_TAIL(to, tob);
 122         }
 123         return (0);
 124 }
 125
 126 void
 127 ttyoutq_free(struct ttyoutq *to)
 128 {
 129         struct ttyoutq_block *tob;
 130
 131         ttyoutq_flush(to);
 132         to->to_quota = 0;
 133
 134         while ((tob = to->to_firstblock) != NULL) {
 135                 TTYOUTQ_REMOVE_HEAD(to);
 136                 uma_zfree(ttyoutq_zone, tob);
 137         }
 138
 139         MPASS(to->to_nblocks == 0);
 140 }
 141
 142 size_t
 143 ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
 144 {
 145         char *cbuf = buf;
 146
 147         while (len > 0) {
 148                 struct ttyoutq_block *tob;
 149                 size_t cbegin, cend, clen;
 150
 151                 /* See if there still is data. */
 152                 if (to->to_begin == to->to_end)
 153                         break;
 154                 tob = to->to_firstblock;
 155                 if (tob == NULL)
 156                         break;
 157
 158                 /*
 159                  * The end address should be the lowest of these three:
 160                  * - The write pointer
 161                  * - The blocksize - we can't read beyond the block
 162                  * - The end address if we could perform the full read
 163                  */
 164                 cbegin = to->to_begin;
 165                 cend = MIN(MIN(to->to_end, to->to_begin + len),
 166                     TTYOUTQ_DATASIZE);
 167                 clen = cend - cbegin;
 168
 169                 /* Copy the data out of the buffers. */
 170                 memcpy(cbuf, tob->tob_data + cbegin, clen);
 171                 cbuf += clen;
 172                 len -= clen;
 173
 174                 if (cend == to->to_end) {
 175                         /* Read the complete queue. */
 176                         to->to_begin = 0;
 177                         to->to_end = 0;
 178                 } else if (cend == TTYOUTQ_DATASIZE) {
 179                         /* Read the block until the end. */
 180                         TTYOUTQ_REMOVE_HEAD(to);
 181                         to->to_begin = 0;
 182                         to->to_end -= TTYOUTQ_DATASIZE;
 183                         TTYOUTQ_RECYCLE(to, tob);
 184                 } else {
 185                         /* Read the block partially. */
 186                         to->to_begin += clen;
 187                 }
 188         }
 189
 190         return (cbuf - (char *)buf);
 191 }
 192
 193 /*
 194  * An optimized version of ttyoutq_read() which can be used in pseudo
 195  * TTY drivers to directly copy data from the outq to userspace, instead
 196  * of buffering it.
 197  *
 198  * We can only copy data directly if we need to read the entire block
 199  * back to the user, because we temporarily remove the block from the
 200  * queue. Otherwise we need to copy it to a temporary buffer first, to
 201  * make sure data remains in the correct order.
 202  */
 203 int
 204 ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
 205 {
 206
 207         while (uio->uio_resid > 0) {
 208                 int error;
 209                 struct ttyoutq_block *tob;
 210                 size_t cbegin, cend, clen;
 211
 212                 /* See if there still is data. */
 213                 if (to->to_begin == to->to_end)
 214                         return (0);
 215                 tob = to->to_firstblock;
 216                 if (tob == NULL)
 217                         return (0);
 218
 219                 /*
 220                  * The end address should be the lowest of these three:
 221                  * - The write pointer
 222                  * - The blocksize - we can't read beyond the block
 223                  * - The end address if we could perform the full read
 224                  */
 225                 cbegin = to->to_begin;
 226                 cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
 227                     TTYOUTQ_DATASIZE);
 228                 clen = cend - cbegin;
 229
 230                 /*
 231                  * We can prevent buffering in some cases:
 232                  * - We need to read the block until the end.
 233                  * - We don't need to read the block until the end, but
 234                  *   there is no data beyond it, which allows us to move
 235                  *   the write pointer to a new block.
 236                  */
 237                 if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
 238                         /*
 239                          * Fast path: zero copy. Remove the first block,
 240                          * so we can unlock the TTY temporarily.
 241                          */
 242                         TTYOUTQ_REMOVE_HEAD(to);
 243                         to->to_begin = 0;
 244                         if (to->to_end <= TTYOUTQ_DATASIZE)
 245                                 to->to_end = 0;
 246                         else
 247                                 to->to_end -= TTYOUTQ_DATASIZE;
 248
 249                         /* Temporary unlock and copy the data to userspace. */
 250                         tty_unlock(tp);
 251                         error = uiomove(tob->tob_data + cbegin, clen, uio);
 252                         tty_lock(tp);
 253
 254                         /* Block can now be readded to the list. */
 255                         TTYOUTQ_RECYCLE(to, tob);
 256                 } else {
 257                         char ob[TTYOUTQ_DATASIZE - 1];
 258
 259                         /*
 260                          * Slow path: store data in a temporary buffer.
 261                          */
 262                         memcpy(ob, tob->tob_data + cbegin, clen);
 263                         to->to_begin += clen;
 264                         MPASS(to->to_begin < TTYOUTQ_DATASIZE);
 265
 266                         /* Temporary unlock and copy the data to userspace. */
 267                         tty_unlock(tp);
 268                         error = uiomove(ob, clen, uio);
 269                         tty_lock(tp);
 270                 }
 271
 272                 if (error != 0)
 273                         return (error);
 274         }
 275
 276         return (0);
 277 }
 278
 279 size_t
 280 ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
 281 {
 282         const char *cbuf = buf;
 283         struct ttyoutq_block *tob;
 284         unsigned int boff;
 285         size_t l;
 286
 287         while (nbytes > 0) {
 288                 boff = to->to_end % TTYOUTQ_DATASIZE;
 289
 290                 if (to->to_end == 0) {
 291                         /* First time we're being used or drained. */
 292                         MPASS(to->to_begin == 0);
 293                         tob = to->to_firstblock;
 294                         if (tob == NULL) {
 295                                 /* Queue has no blocks. */
 296                                 break;
 297                         }
 298                         to->to_lastblock = tob;
 299                 } else if (boff == 0) {
 300                         /* We reached the end of this block on last write. */
 301                         tob = to->to_lastblock->tob_next;
 302                         if (tob == NULL) {
 303                                 /* We've reached the watermark. */
 304                                 break;
 305                         }
 306                         to->to_lastblock = tob;
 307                 } else {
 308                         tob = to->to_lastblock;
 309                 }
 310
 311                 /* Don't copy more than was requested. */
 312                 l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
 313                 MPASS(l > 0);
 314                 memcpy(tob->tob_data + boff, cbuf, l);
 315
 316                 cbuf += l;
 317                 nbytes -= l;
 318                 to->to_end += l;
 319         }
 320
 321         return (cbuf - (const char *)buf);
 322 }
 323
 324 int
 325 ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
 326 {
 327         size_t ret __unused;
 328
 329         if (ttyoutq_bytesleft(to) < nbytes)
 330                 return (-1);
 331
 332         /* We should always be able to write it back. */
 333         ret = ttyoutq_write(to, buf, nbytes);
 334         MPASS(ret == nbytes);
 335
 336         return (0);
 337 }
 338
 339 static void
 340 ttyoutq_startup(void *dummy)
 341 {
 342
 343         ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
 344             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
 345 }
 346
 347 SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);