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 void
  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                 TTYOUTQ_INSERT_TAIL(to, tob);
 115         }
 116 }
 117
 118 void
 119 ttyoutq_free(struct ttyoutq *to)
 120 {
 121         struct ttyoutq_block *tob;
 122
 123         ttyoutq_flush(to);
 124         to->to_quota = 0;
 125
 126         while ((tob = to->to_firstblock) != NULL) {
 127                 TTYOUTQ_REMOVE_HEAD(to);
 128                 uma_zfree(ttyoutq_zone, tob);
 129         }
 130
 131         MPASS(to->to_nblocks == 0);
 132 }
 133
 134 size_t
 135 ttyoutq_read(struct ttyoutq *to, void *buf, size_t len)
 136 {
 137         char *cbuf = buf;
 138
 139         while (len > 0) {
 140                 struct ttyoutq_block *tob;
 141                 size_t cbegin, cend, clen;
 142
 143                 /* See if there still is data. */
 144                 if (to->to_begin == to->to_end)
 145                         break;
 146                 tob = to->to_firstblock;
 147                 if (tob == NULL)
 148                         break;
 149
 150                 /*
 151                  * The end address should be the lowest of these three:
 152                  * - The write pointer
 153                  * - The blocksize - we can't read beyond the block
 154                  * - The end address if we could perform the full read
 155                  */
 156                 cbegin = to->to_begin;
 157                 cend = MIN(MIN(to->to_end, to->to_begin + len),
 158                     TTYOUTQ_DATASIZE);
 159                 clen = cend - cbegin;
 160
 161                 /* Copy the data out of the buffers. */
 162                 memcpy(cbuf, tob->tob_data + cbegin, clen);
 163                 cbuf += clen;
 164                 len -= clen;
 165
 166                 if (cend == to->to_end) {
 167                         /* Read the complete queue. */
 168                         to->to_begin = 0;
 169                         to->to_end = 0;
 170                 } else if (cend == TTYOUTQ_DATASIZE) {
 171                         /* Read the block until the end. */
 172                         TTYOUTQ_REMOVE_HEAD(to);
 173                         to->to_begin = 0;
 174                         to->to_end -= TTYOUTQ_DATASIZE;
 175                         TTYOUTQ_RECYCLE(to, tob);
 176                 } else {
 177                         /* Read the block partially. */
 178                         to->to_begin += clen;
 179                 }
 180         }
 181
 182         return (cbuf - (char *)buf);
 183 }
 184
 185 /*
 186  * An optimized version of ttyoutq_read() which can be used in pseudo
 187  * TTY drivers to directly copy data from the outq to userspace, instead
 188  * of buffering it.
 189  *
 190  * We can only copy data directly if we need to read the entire block
 191  * back to the user, because we temporarily remove the block from the
 192  * queue. Otherwise we need to copy it to a temporary buffer first, to
 193  * make sure data remains in the correct order.
 194  */
 195 int
 196 ttyoutq_read_uio(struct ttyoutq *to, struct tty *tp, struct uio *uio)
 197 {
 198
 199         while (uio->uio_resid > 0) {
 200                 int error;
 201                 struct ttyoutq_block *tob;
 202                 size_t cbegin, cend, clen;
 203
 204                 /* See if there still is data. */
 205                 if (to->to_begin == to->to_end)
 206                         return (0);
 207                 tob = to->to_firstblock;
 208                 if (tob == NULL)
 209                         return (0);
 210
 211                 /*
 212                  * The end address should be the lowest of these three:
 213                  * - The write pointer
 214                  * - The blocksize - we can't read beyond the block
 215                  * - The end address if we could perform the full read
 216                  */
 217                 cbegin = to->to_begin;
 218                 cend = MIN(MIN(to->to_end, to->to_begin + uio->uio_resid),
 219                     TTYOUTQ_DATASIZE);
 220                 clen = cend - cbegin;
 221
 222                 /*
 223                  * We can prevent buffering in some cases:
 224                  * - We need to read the block until the end.
 225                  * - We don't need to read the block until the end, but
 226                  *   there is no data beyond it, which allows us to move
 227                  *   the write pointer to a new block.
 228                  */
 229                 if (cend == TTYOUTQ_DATASIZE || cend == to->to_end) {
 230                         /*
 231                          * Fast path: zero copy. Remove the first block,
 232                          * so we can unlock the TTY temporarily.
 233                          */
 234                         TTYOUTQ_REMOVE_HEAD(to);
 235                         to->to_begin = 0;
 236                         if (to->to_end <= TTYOUTQ_DATASIZE)
 237                                 to->to_end = 0;
 238                         else
 239                                 to->to_end -= TTYOUTQ_DATASIZE;
 240
 241                         /* Temporary unlock and copy the data to userspace. */
 242                         tty_unlock(tp);
 243                         error = uiomove(tob->tob_data + cbegin, clen, uio);
 244                         tty_lock(tp);
 245
 246                         /* Block can now be readded to the list. */
 247                         TTYOUTQ_RECYCLE(to, tob);
 248                 } else {
 249                         char ob[TTYOUTQ_DATASIZE - 1];
 250
 251                         /*
 252                          * Slow path: store data in a temporary buffer.
 253                          */
 254                         memcpy(ob, tob->tob_data + cbegin, clen);
 255                         to->to_begin += clen;
 256                         MPASS(to->to_begin < TTYOUTQ_DATASIZE);
 257
 258                         /* Temporary unlock and copy the data to userspace. */
 259                         tty_unlock(tp);
 260                         error = uiomove(ob, clen, uio);
 261                         tty_lock(tp);
 262                 }
 263
 264                 if (error != 0)
 265                         return (error);
 266         }
 267
 268         return (0);
 269 }
 270
 271 size_t
 272 ttyoutq_write(struct ttyoutq *to, const void *buf, size_t nbytes)
 273 {
 274         const char *cbuf = buf;
 275         struct ttyoutq_block *tob;
 276         unsigned int boff;
 277         size_t l;
 278
 279         while (nbytes > 0) {
 280                 boff = to->to_end % TTYOUTQ_DATASIZE;
 281
 282                 if (to->to_end == 0) {
 283                         /* First time we're being used or drained. */
 284                         MPASS(to->to_begin == 0);
 285                         tob = to->to_firstblock;
 286                         if (tob == NULL) {
 287                                 /* Queue has no blocks. */
 288                                 break;
 289                         }
 290                         to->to_lastblock = tob;
 291                 } else if (boff == 0) {
 292                         /* We reached the end of this block on last write. */
 293                         tob = to->to_lastblock->tob_next;
 294                         if (tob == NULL) {
 295                                 /* We've reached the watermark. */
 296                                 break;
 297                         }
 298                         to->to_lastblock = tob;
 299                 } else {
 300                         tob = to->to_lastblock;
 301                 }
 302
 303                 /* Don't copy more than was requested. */
 304                 l = MIN(nbytes, TTYOUTQ_DATASIZE - boff);
 305                 MPASS(l > 0);
 306                 memcpy(tob->tob_data + boff, cbuf, l);
 307
 308                 cbuf += l;
 309                 nbytes -= l;
 310                 to->to_end += l;
 311         }
 312
 313         return (cbuf - (const char *)buf);
 314 }
 315
 316 int
 317 ttyoutq_write_nofrag(struct ttyoutq *to, const void *buf, size_t nbytes)
 318 {
 319         size_t ret;
 320
 321         if (ttyoutq_bytesleft(to) < nbytes)
 322                 return (-1);
 323
 324         /* We should always be able to write it back. */
 325         ret = ttyoutq_write(to, buf, nbytes);
 326         MPASS(ret == nbytes);
 327
 328         return (0);
 329 }
 330
 331 static void
 332 ttyoutq_startup(void *dummy)
 333 {
 334
 335         ttyoutq_zone = uma_zcreate("ttyoutq", sizeof(struct ttyoutq_block),
 336             NULL, NULL, NULL, NULL, UMA_ALIGN_PTR, 0);
 337 }
 338
 339 SYSINIT(ttyoutq, SI_SUB_DRIVERS, SI_ORDER_FIRST, ttyoutq_startup, NULL);