sys/kern/tty_outq.c

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