usr.bin/tail/forward.c

   1 /*      $NetBSD: forward.c,v 1.28 2006/05/24 16:34:25 christos Exp $    */
   2
   3 /*-
   4  * Copyright (c) 1991, 1993
   5  *      The Regents of the University of California.  All rights reserved.
   6  *
   7  * This code is derived from software contributed to Berkeley by
   8  * Edward Sze-Tyan Wang.
   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  * 3. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #ifndef lint
  37 #if 0
  38 static char sccsid[] = "@(#)forward.c   8.1 (Berkeley) 6/6/93";
  39 #endif
  40 __RCSID("$NetBSD: forward.c,v 1.28 2006/05/24 16:34:25 christos Exp $");
  41 #endif /* not lint */
  42
  43 #include <sys/types.h>
  44 #include <sys/stat.h>
  45 #include <sys/time.h>
  46 #include <sys/mman.h>
  47 #include <sys/event.h>
  48
  49 #include <limits.h>
  50 #include <fcntl.h>
  51 #include <errno.h>
  52 #include <unistd.h>
  53 #include <stdio.h>
  54 #include <stdlib.h>
  55 #include <string.h>
  56 #include "extern.h"
  57
  58 static int rlines(FILE *, off_t, struct stat *);
  59
  60 /* defines for inner loop actions */
  61 #define USE_SLEEP       0
  62 #define USE_KQUEUE      1
  63 #define ADD_EVENTS      2
  64
  65 /*
  66  * forward -- display the file, from an offset, forward.
  67  *
  68  * There are eight separate cases for this -- regular and non-regular
  69  * files, by bytes or lines and from the beginning or end of the file.
  70  *
  71  * FBYTES       byte offset from the beginning of the file
  72  *      REG     seek
  73  *      NOREG   read, counting bytes
  74  *
  75  * FLINES       line offset from the beginning of the file
  76  *      REG     read, counting lines
  77  *      NOREG   read, counting lines
  78  *
  79  * RBYTES       byte offset from the end of the file
  80  *      REG     seek
  81  *      NOREG   cyclically read characters into a wrap-around buffer
  82  *
  83  * RLINES
  84  *      REG     mmap the file and step back until reach the correct offset.
  85  *      NOREG   cyclically read lines into a wrap-around array of buffers
  86  */
  87 void
  88 forward(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
  89 {
  90         int ch, n;
  91         int kq=-1, action=USE_SLEEP;
  92         struct stat statbuf;
  93         dev_t lastdev;
  94         ino_t lastino;
  95         struct kevent ev[2];
  96
  97         /* Keep track of file's previous incarnation. */
  98         lastdev = sbp->st_dev;
  99         lastino = sbp->st_ino;
 100
 101         switch(style) {
 102         case FBYTES:
 103                 if (off == 0)
 104                         break;
 105                 if (S_ISREG(sbp->st_mode)) {
 106                         if (sbp->st_size < off)
 107                                 off = sbp->st_size;
 108                         if (fseeko(fp, off, SEEK_SET) == -1) {
 109                                 ierr();
 110                                 return;
 111                         }
 112                 } else while (off--)
 113                         if ((ch = getc(fp)) == EOF) {
 114                                 if (ferror(fp)) {
 115                                         ierr();
 116                                         return;
 117                                 }
 118                                 break;
 119                         }
 120                 break;
 121         case FLINES:
 122                 if (off == 0)
 123                         break;
 124                 for (;;) {
 125                         if ((ch = getc(fp)) == EOF) {
 126                                 if (ferror(fp)) {
 127                                         ierr();
 128                                         return;
 129                                 }
 130                                 break;
 131                         }
 132                         if (ch == '\n' && !--off)
 133                                 break;
 134                 }
 135                 break;
 136         case RBYTES:
 137                 if (S_ISREG(sbp->st_mode)) {
 138                         if (sbp->st_size >= off &&
 139                             fseeko(fp, -off, SEEK_END) == -1) {
 140                                 ierr();
 141                                 return;
 142                         }
 143                 } else if (off == 0) {
 144                         while (getc(fp) != EOF);
 145                         if (ferror(fp)) {
 146                                 ierr();
 147                                 return;
 148                         }
 149                 } else {
 150                         if (displaybytes(fp, off))
 151                                 return;
 152                 }
 153                 break;
 154         case RLINES:
 155                 if (S_ISREG(sbp->st_mode)) {
 156                         if (!off) {
 157                                 if (fseek(fp, 0L, SEEK_END) == -1) {
 158                                         ierr();
 159                                         return;
 160                                 }
 161                         } else {
 162                                 if (rlines(fp, off, sbp))
 163                                         return;
 164                         }
 165                 } else if (off == 0) {
 166                         while (getc(fp) != EOF);
 167                         if (ferror(fp)) {
 168                                 ierr();
 169                                 return;
 170                         }
 171                 } else {
 172                         if (displaylines(fp, off))
 173                                 return;
 174                 }
 175                 break;
 176         default:
 177                 break;
 178         }
 179
 180         if (fflag) {
 181                 kq = kqueue();
 182                 if (kq < 0)
 183                         err(1, "kqueue");
 184                 action = ADD_EVENTS;
 185         }
 186
 187         for (;;) {
 188                 while ((ch = getc(fp)) != EOF)  {
 189                         if (putchar(ch) == EOF)
 190                                 oerr();
 191                 }
 192                 if (ferror(fp)) {
 193                         ierr();
 194                         return;
 195                 }
 196                 (void)fflush(stdout);
 197                 if (!fflag)
 198                         break;
 199
 200                 clearerr(fp);
 201
 202                 switch (action) {
 203                 case ADD_EVENTS:
 204                         n = 0;
 205
 206                         memset(ev, 0, sizeof(ev));
 207                         if (fflag == 2 && fileno(fp) != STDIN_FILENO) {
 208                                 EV_SET(&ev[n], fileno(fp), EVFILT_VNODE,
 209                                         EV_ADD | EV_ENABLE | EV_CLEAR,
 210                                         NOTE_DELETE | NOTE_RENAME, 0, 0);
 211                                 n++;
 212                         }
 213                         EV_SET(&ev[n], fileno(fp), EVFILT_READ,
 214                                 EV_ADD | EV_ENABLE, 0, 0, 0);
 215                         n++;
 216
 217                         if (kevent(kq, ev, n, NULL, 0, NULL) < 0) {
 218                                 close(kq);
 219                                 kq = -1;
 220                                 action = USE_SLEEP;
 221                         } else {
 222                                 action = USE_KQUEUE;
 223                         }
 224                         break;
 225
 226                 case USE_KQUEUE:
 227                         if (kevent(kq, NULL, 0, ev, 1, NULL) < 0)
 228                                 err(1, "kevent");
 229
 230                         if (ev[0].filter == EVFILT_VNODE) {
 231                                 /* file was rotated, wait until it reappears */
 232                                 action = USE_SLEEP;
 233                         } else if (ev[0].data < 0) {
 234                                 /* file shrank, reposition to end */
 235                                 if (fseek(fp, 0L, SEEK_END) == -1) {
 236                                         ierr();
 237                                         return;
 238                                 }
 239                         }
 240                         break;
 241
 242                 case USE_SLEEP:
 243                         /*
 244                          * We pause for one second after displaying any data
 245                          * that has accumulated since we read the file.
 246                          */
 247                         (void) sleep(1);
 248
 249                         if (fflag == 2 && fileno(fp) != STDIN_FILENO &&
 250                             stat(fname, &statbuf) != -1) {
 251                                 if (statbuf.st_ino != sbp->st_ino ||
 252                                     statbuf.st_dev != sbp->st_dev ||
 253                                     statbuf.st_rdev != sbp->st_rdev ||
 254                                     statbuf.st_nlink == 0) {
 255                                         fp = freopen(fname, "r", fp);
 256                                         if (fp == NULL) {
 257                                                 ierr();
 258                                                 goto out;
 259                                         }
 260                                         *sbp = statbuf;
 261                                         if (kq != -1)
 262                                                 action = ADD_EVENTS;
 263                                 } else if (kq != -1)
 264                                         action = USE_KQUEUE;
 265                         }
 266                         break;
 267                 }
 268         }
 269 out:
 270         if (fflag && kq != -1)
 271                 close(kq);
 272 }
 273
 274 /*
 275  * rlines -- display the last offset lines of the file.
 276  *
 277  * Non-zero return means than a (non-fatal) error occurred.
 278  */
 279 static int
 280 rlines(FILE *fp, off_t off, struct stat *sbp)
 281 {
 282         off_t file_size;
 283         off_t file_remaining;
 284         char *p = NULL;
 285         char *start = NULL;
 286         off_t mmap_size;
 287         off_t mmap_offset;
 288         off_t mmap_remaining = 0;
 289
 290 #define MMAP_MAXSIZE  (10 * 1024 * 1024)
 291
 292         if (!(file_size = sbp->st_size))
 293                 return (0);
 294         file_remaining = file_size;
 295
 296         if (file_remaining > MMAP_MAXSIZE) {
 297                 mmap_size = MMAP_MAXSIZE;
 298                 mmap_offset = file_remaining - MMAP_MAXSIZE;
 299         } else {
 300                 mmap_size = file_remaining;
 301                 mmap_offset = 0;
 302         }
 303
 304         while (off) {
 305                 start = mmap(NULL, (size_t)mmap_size, PROT_READ,
 306                              MAP_FILE|MAP_SHARED, fileno(fp), mmap_offset);
 307                 if (start == MAP_FAILED) {
 308                         err(0, "%s: %s", fname, strerror(EFBIG));
 309                         return (1);
 310                 }
 311
 312                 mmap_remaining = mmap_size;
 313                 /* Last char is special, ignore whether newline or not. */
 314                 for (p = start + mmap_remaining - 1 ; --mmap_remaining ; )
 315                         if (*--p == '\n' && !--off) {
 316                                 ++p;
 317                                 break;
 318                         }
 319
 320                 file_remaining -= mmap_size - mmap_remaining;
 321
 322                 if (off == 0)
 323                         break;
 324
 325                 if (file_remaining == 0)
 326                         break;
 327
 328                 if (munmap(start, mmap_size)) {
 329                         err(0, "%s: %s", fname, strerror(errno));
 330                         return (1);
 331                 }
 332
 333                 if (mmap_offset >= MMAP_MAXSIZE) {
 334                         mmap_offset -= MMAP_MAXSIZE;
 335                 } else {
 336                         mmap_offset = 0;
 337                         mmap_size = file_remaining;
 338                 }
 339         }
 340
 341         /*
 342          * Output the (perhaps partial) data in this mmap'd block.
 343          */
 344         WR(p, mmap_size - mmap_remaining);
 345         file_remaining += mmap_size - mmap_remaining;
 346         if (munmap(start, mmap_size)) {
 347                 err(0, "%s: %s", fname, strerror(errno));
 348                 return (1);
 349         }
 350
 351         /*
 352          * Set the file pointer to reflect the length displayed.
 353          * This will cause the caller to redisplay the data if/when
 354          * needed.
 355          */
 356         if (fseeko(fp, file_remaining, SEEK_SET) == -1) {
 357                 ierr();
 358                 return (1);
 359         }
 360         return (0);
 361 }