usr.bin/tail/forward.c

   1 /*-
   2  * Copyright (c) 1991, 1993
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   5  * This code is derived from software contributed to Berkeley by
   6  * Edward Sze-Tyan Wang.
   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  * 3. All advertising materials mentioning features or use of this software
  17  *    must display the following acknowledgement:
  18  *      This product includes software developed by the University of
  19  *      California, Berkeley and its contributors.
  20  * 4. Neither the name of the University nor the names of its contributors
  21  *    may be used to endorse or promote products derived from this software
  22  *    without specific prior written permission.
  23  *
  24  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  25  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  26  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  27  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  28  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  29  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  30  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  31  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  32  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  33  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  34  * SUCH DAMAGE.
  35  *
  36  * $FreeBSD$
  37  */
  38
  39 #ifndef lint
  40 static char sccsid[] = "@(#)forward.c   8.1 (Berkeley) 6/6/93";
  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 <err.h>
  57 #include "extern.h"
  58
  59 static void rlines __P((FILE *, long, struct stat *));
  60
  61 /* defines for inner loop actions */
  62 #define USE_SLEEP       0
  63 #define USE_KQUEUE      1
  64 #define ADD_EVENTS      2
  65
  66 /*
  67  * forward -- display the file, from an offset, forward.
  68  *
  69  * There are eight separate cases for this -- regular and non-regular
  70  * files, by bytes or lines and from the beginning or end of the file.
  71  *
  72  * FBYTES       byte offset from the beginning of the file
  73  *      REG     seek
  74  *      NOREG   read, counting bytes
  75  *
  76  * FLINES       line offset from the beginning of the file
  77  *      REG     read, counting lines
  78  *      NOREG   read, counting lines
  79  *
  80  * RBYTES       byte offset from the end of the file
  81  *      REG     seek
  82  *      NOREG   cyclically read characters into a wrap-around buffer
  83  *
  84  * RLINES
  85  *      REG     mmap the file and step back until reach the correct offset.
  86  *      NOREG   cyclically read lines into a wrap-around array of buffers
  87  */
  88 void
  89 forward(fp, style, off, sbp)
  90         FILE *fp;
  91         enum STYLE style;
  92         long off;
  93         struct stat *sbp;
  94 {
  95         int ch, kq = -1;
  96         int action = USE_SLEEP;
  97         struct kevent ev[2];
  98         struct stat sb2;
  99
 100         switch(style) {
 101         case FBYTES:
 102                 if (off == 0)
 103                         break;
 104                 if (S_ISREG(sbp->st_mode)) {
 105                         if (sbp->st_size < off)
 106                                 off = sbp->st_size;
 107                         if (fseek(fp, off, SEEK_SET) == -1) {
 108                                 ierr();
 109                                 return;
 110                         }
 111                 } else while (off--)
 112                         if ((ch = getc(fp)) == EOF) {
 113                                 if (ferror(fp)) {
 114                                         ierr();
 115                                         return;
 116                                 }
 117                                 break;
 118                         }
 119                 break;
 120         case FLINES:
 121                 if (off == 0)
 122                         break;
 123                 for (;;) {
 124                         if ((ch = getc(fp)) == EOF) {
 125                                 if (ferror(fp)) {
 126                                         ierr();
 127                                         return;
 128                                 }
 129                                 break;
 130                         }
 131                         if (ch == '\n' && !--off)
 132                                 break;
 133                 }
 134                 break;
 135         case RBYTES:
 136                 if (S_ISREG(sbp->st_mode)) {
 137                         if (sbp->st_size >= off &&
 138                             fseek(fp, -off, SEEK_END) == -1) {
 139                                 ierr();
 140                                 return;
 141                         }
 142                 } else if (off == 0) {
 143                         while (getc(fp) != EOF);
 144                         if (ferror(fp)) {
 145                                 ierr();
 146                                 return;
 147                         }
 148                 } else
 149                         if (bytes(fp, off))
 150                                 return;
 151                 break;
 152         case RLINES:
 153                 if (S_ISREG(sbp->st_mode))
 154                         if (!off) {
 155                                 if (fseek(fp, 0L, SEEK_END) == -1) {
 156                                         ierr();
 157                                         return;
 158                                 }
 159                         } else
 160                                 rlines(fp, off, sbp);
 161                 else if (off == 0) {
 162                         while (getc(fp) != EOF);
 163                         if (ferror(fp)) {
 164                                 ierr();
 165                                 return;
 166                         }
 167                 } else
 168                         if (lines(fp, off))
 169                                 return;
 170                 break;
 171         }
 172
 173         if (fflag) {
 174                 kq = kqueue();
 175                 if (kq < 0)
 176                         err(1, "kqueue");
 177                 action = ADD_EVENTS;
 178         }
 179
 180         for (;;) {
 181                 while ((ch = getc(fp)) != EOF)
 182                         if (putchar(ch) == EOF)
 183                                 oerr();
 184                 if (ferror(fp)) {
 185                         ierr();
 186                         return;
 187                 }
 188                 (void)fflush(stdout);
 189                 if (! fflag)
 190                         break;
 191                 clearerr(fp);
 192
 193                 switch (action) {
 194                 case ADD_EVENTS: {
 195                         int n = 0;
 196                         struct timespec ts = { 0, 0 };
 197
 198                         if (Fflag && fileno(fp) != STDIN_FILENO) {
 199                                 ev[n].ident = fileno(fp);
 200                                 ev[n].filter = EVFILT_VNODE;
 201                                 ev[n].flags = EV_ADD | EV_ENABLE | EV_CLEAR;
 202                                 ev[n].fflags = NOTE_DELETE | NOTE_RENAME;
 203                                 n++;
 204                         }
 205                         ev[n].ident = fileno(fp);
 206                         ev[n].filter = EVFILT_READ;
 207                         ev[n].flags = EV_ADD | EV_ENABLE;
 208                         n++;
 209
 210                         if (kevent(kq, ev, n, NULL, 0, &ts) < 0) {
 211                                 close(kq);
 212                                 kq = -1;
 213                                 action = USE_SLEEP;
 214                         } else {
 215                                 action = USE_KQUEUE;
 216                         }
 217                         break;
 218                 }
 219
 220                 case USE_KQUEUE:
 221                         if (kevent(kq, NULL, 0, ev, 1, NULL) < 0)
 222                                 err(1, "kevent");
 223
 224                         if (ev->filter == EVFILT_VNODE) {
 225                                 /* file was rotated, wait until it reappears */
 226                                 action = USE_SLEEP;
 227                         } else if (ev->data < 0) {
 228                                 /* file shrank, reposition to end */
 229                                 if (fseek(fp, 0L, SEEK_END) == -1) {
 230                                         ierr();
 231                                         return;
 232                                 }
 233                         }
 234                         break;
 235
 236                 case USE_SLEEP:
 237                         (void) usleep(250000);
 238                         clearerr(fp);
 239
 240                         if (Fflag && fileno(fp) != STDIN_FILENO &&
 241                             stat(fname, &sb2) != -1) {
 242                                 if (sb2.st_ino != sbp->st_ino ||
 243                                     sb2.st_dev != sbp->st_dev ||
 244                                     sb2.st_rdev != sbp->st_rdev ||
 245                                     sb2.st_nlink == 0) {
 246                                         fp = freopen(fname, "r", fp);
 247                                         if (fp == NULL) {
 248                                                 ierr();
 249                                                 break;
 250                                         }
 251                                         *sbp = sb2;
 252                                         if (kq != -1)
 253                                                 action = ADD_EVENTS;
 254                                 }
 255                         }
 256                         break;
 257                 }
 258         }
 259 }
 260
 261 /*
 262  * rlines -- display the last offset lines of the file.
 263  */
 264 static void
 265 rlines(fp, off, sbp)
 266         FILE *fp;
 267         long off;
 268         struct stat *sbp;
 269 {
 270         register off_t size;
 271         register char *p;
 272         char *start;
 273
 274         if (!(size = sbp->st_size))
 275                 return;
 276
 277         if (size > SIZE_T_MAX) {
 278                 errno = EFBIG;
 279                 ierr();
 280                 return;
 281         }
 282
 283         if ((start = mmap(NULL, (size_t)size,
 284             PROT_READ, MAP_SHARED, fileno(fp), (off_t)0)) == MAP_FAILED) {
 285                 ierr();
 286                 return;
 287         }
 288
 289         /* Last char is special, ignore whether newline or not. */
 290         for (p = start + size - 1; --size;)
 291                 if (*--p == '\n' && !--off) {
 292                         ++p;
 293                         break;
 294                 }
 295
 296         /* Set the file pointer to reflect the length displayed. */
 297         size = sbp->st_size - size;
 298         WR(p, size);
 299         if (fseek(fp, (long)sbp->st_size, SEEK_SET) == -1) {
 300                 ierr();
 301                 return;
 302         }
 303         if (munmap(start, (size_t)sbp->st_size)) {
 304                 ierr();
 305                 return;
 306         }
 307 }