usr.bin/tail/forward.c

   1 /*      $NetBSD: forward.c,v 1.33 2015/10/09 17:51:26 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 1.33 2015/10/09 17:51:26 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 #if !defined(__minix)
  91         int ch, n;
  92 #else
  93         int ch;
  94 #endif /* !defined(__minix) */
  95         int kq=-1, action=USE_SLEEP;
  96         struct stat statbuf;
  97 #if !defined(__minix)
  98         struct kevent ev[2];
  99 #endif /* !defined(__minix) */
 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 #if !defined(__minix)
 182                 kq = kqueue();
 183                 if (kq < 0)
 184                         xerr(1, "kqueue");
 185                 action = ADD_EVENTS;
 186 #else
 187         action = USE_SLEEP;
 188 #endif /* !defined(__minix) */
 189         }
 190
 191         for (;;) {
 192                 while ((ch = getc(fp)) != EOF)  {
 193                         if (putchar(ch) == EOF)
 194                                 oerr();
 195                 }
 196                 if (ferror(fp)) {
 197                         ierr();
 198                         return;
 199                 }
 200                 (void)fflush(stdout);
 201                 if (!fflag)
 202                         break;
 203
 204                 clearerr(fp);
 205
 206                 switch (action) {
 207 #if !defined(__minix)
 208                 case ADD_EVENTS:
 209                         n = 0;
 210
 211                         memset(ev, 0, sizeof(ev));
 212                         if (fflag == 2 && fp != stdin) {
 213                                 EV_SET(&ev[n], fileno(fp), EVFILT_VNODE,
 214                                     EV_ADD | EV_ENABLE | EV_CLEAR,
 215                                     NOTE_DELETE | NOTE_RENAME, 0, 0);
 216                                 n++;
 217                         }
 218                         EV_SET(&ev[n], fileno(fp), EVFILT_READ,
 219                             EV_ADD | EV_ENABLE, 0, 0, 0);
 220                         n++;
 221
 222                         if (kevent(kq, ev, n, NULL, 0, NULL) == -1) {
 223                                 close(kq);
 224                                 kq = -1;
 225                                 action = USE_SLEEP;
 226                         } else {
 227                                 action = USE_KQUEUE;
 228                         }
 229                         break;
 230
 231                 case USE_KQUEUE:
 232                         if (kevent(kq, NULL, 0, ev, 1, NULL) == -1)
 233                                 xerr(1, "kevent");
 234
 235                         if (ev[0].filter == EVFILT_VNODE) {
 236                                 /* file was rotated, wait until it reappears */
 237                                 action = USE_SLEEP;
 238                         } else if (ev[0].data < 0) {
 239                                 /* file shrank, reposition to end */
 240                                 if (fseek(fp, 0L, SEEK_END) == -1) {
 241                                         ierr();
 242                                         return;
 243                                 }
 244                         }
 245                         break;
 246 #endif /* !defined(__minix) */
 247
 248                 case USE_SLEEP:
 249                         /*
 250                          * We pause for one second after displaying any data
 251                          * that has accumulated since we read the file.
 252                          */
 253                         (void) sleep(1);
 254
 255                         if (fflag == 2 && fp != stdin &&
 256                             stat(fname, &statbuf) != -1) {
 257                                 if (statbuf.st_ino != sbp->st_ino ||
 258                                     statbuf.st_dev != sbp->st_dev ||
 259                                     statbuf.st_rdev != sbp->st_rdev ||
 260                                     statbuf.st_nlink == 0) {
 261                                         fp = freopen(fname, "r", fp);
 262                                         if (fp == NULL) {
 263                                                 ierr();
 264                                                 goto out;
 265                                         }
 266                                         *sbp = statbuf;
 267                                         if (kq != -1)
 268                                                 action = ADD_EVENTS;
 269                                 } else if (kq != -1)
 270                                         action = USE_KQUEUE;
 271                         }
 272                         break;
 273                 }
 274         }
 275 out:
 276         if (fflag && kq != -1)
 277                 close(kq);
 278 }
 279
 280 /*
 281  * rlines -- display the last offset lines of the file.
 282  *
 283  * Non-zero return means than a (non-fatal) error occurred.
 284  */
 285 static int
 286 rlines(FILE *fp, off_t off, struct stat *sbp)
 287 {
 288         off_t file_size;
 289         off_t file_remaining;
 290         char *p = NULL;
 291         char *start = NULL;
 292         off_t mmap_size;
 293         off_t mmap_offset;
 294         off_t mmap_remaining = 0;
 295
 296 #define MMAP_MAXSIZE  (10 * 1024 * 1024)
 297
 298         if (!(file_size = sbp->st_size))
 299                 return 0;
 300         file_remaining = file_size;
 301
 302         if (file_remaining > MMAP_MAXSIZE) {
 303                 mmap_size = MMAP_MAXSIZE;
 304                 mmap_offset = file_remaining - MMAP_MAXSIZE;
 305         } else {
 306                 mmap_size = file_remaining;
 307                 mmap_offset = 0;
 308         }
 309
 310         while (off) {
 311                 start = mmap(NULL, (size_t)mmap_size, PROT_READ,
 312                              MAP_FILE|MAP_SHARED, fileno(fp), mmap_offset);
 313                 if (start == MAP_FAILED) {
 314                         xerr(0, "%s", fname);
 315                         return 1;
 316                 }
 317
 318                 mmap_remaining = mmap_size;
 319                 /* Last char is special, ignore whether newline or not. */
 320                 for (p = start + mmap_remaining - 1 ; --mmap_remaining ; )
 321                         if (*--p == '\n' && !--off) {
 322                                 ++p;
 323                                 break;
 324                         }
 325
 326                 file_remaining -= mmap_size - mmap_remaining;
 327
 328                 if (off == 0)
 329                         break;
 330
 331                 if (file_remaining == 0)
 332                         break;
 333
 334                 if (munmap(start, mmap_size)) {
 335                         xerr(0, "%s", fname);
 336                         return 1;
 337                 }
 338
 339                 if (mmap_offset >= MMAP_MAXSIZE) {
 340                         mmap_offset -= MMAP_MAXSIZE;
 341                 } else {
 342                         mmap_offset = 0;
 343                         mmap_size = file_remaining;
 344                 }
 345         }
 346
 347         /*
 348          * Output the (perhaps partial) data in this mmap'd block.
 349          */
 350         WR(p, mmap_size - mmap_remaining);
 351         file_remaining += mmap_size - mmap_remaining;
 352         if (munmap(start, mmap_size)) {
 353                 xerr(0, "%s", fname);
 354                 return 1;
 355         }
 356
 357         /*
 358          * Set the file pointer to reflect the length displayed.
 359          * This will cause the caller to redisplay the data if/when
 360          * needed.
 361          */
 362         if (fseeko(fp, file_remaining, SEEK_SET) == -1) {
 363                 ierr();
 364                 return 1;
 365         }
 366         return 0;
 367 }