usr.bin/tail/reverse.c

   1 /*      $NetBSD: reverse.c,v 1.19 2006/04/09 19:39:17 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[] = "@(#)reverse.c   8.1 (Berkeley) 6/6/93";
  39 #endif
  40 __RCSID("$NetBSD: reverse.c,v 1.19 2006/04/09 19:39:17 christos Exp $");
  41 #endif /* not lint */
  42
  43 #include <sys/param.h>
  44 #include <sys/stat.h>
  45 #include <sys/mman.h>
  46
  47 #include <limits.h>
  48 #include <errno.h>
  49 #include <unistd.h>
  50 #include <stdio.h>
  51 #include <stdlib.h>
  52 #include <string.h>
  53 #include "extern.h"
  54
  55 static void r_buf(FILE *);
  56 static void r_reg(FILE *, enum STYLE, off_t, struct stat *);
  57
  58 /*
  59  * reverse -- display input in reverse order by line.
  60  *
  61  * There are six separate cases for this -- regular and non-regular
  62  * files by bytes, lines or the whole file.
  63  *
  64  * BYTES        display N bytes
  65  *      REG     mmap the file and display the lines
  66  *      NOREG   cyclically read characters into a wrap-around buffer
  67  *
  68  * LINES        display N lines
  69  *      REG     mmap the file and display the lines
  70  *      NOREG   cyclically read lines into a wrap-around array of buffers
  71  *
  72  * FILE         display the entire file
  73  *      REG     mmap the file and display the lines
  74  *      NOREG   cyclically read input into a linked list of buffers
  75  */
  76 void
  77 reverse(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
  78 {
  79         if (style != REVERSE && off == 0)
  80                 return;
  81
  82         if (S_ISREG(sbp->st_mode))
  83                 r_reg(fp, style, off, sbp);
  84         else
  85                 switch(style) {
  86                 case FBYTES:
  87                 case RBYTES:
  88                         (void)displaybytes(fp, off);
  89                         break;
  90                 case FLINES:
  91                 case RLINES:
  92                         (void)displaylines(fp, off);
  93                         break;
  94                 case REVERSE:
  95                         r_buf(fp);
  96                         break;
  97                 default:
  98                         break;
  99                 }
 100 }
 101
 102 /*
 103  * r_reg -- display a regular file in reverse order by line.
 104  */
 105 static void
 106 r_reg(FILE *fp, enum STYLE style, off_t off, struct stat *sbp)
 107 {
 108         off_t size;
 109         int llen;
 110         char *p;
 111         char *start;
 112
 113         if (!(size = sbp->st_size))
 114                 return;
 115
 116         if ((uint64_t)size > SIZE_T_MAX) {
 117                         /* XXX: need a cleaner way to check this on amd64 */
 118                 err(0, "%s: %s", fname, strerror(EFBIG));
 119                 return;
 120         }
 121
 122         if ((start = mmap(NULL, (size_t)size, PROT_READ,
 123             MAP_FILE|MAP_SHARED, fileno(fp), (off_t)0)) == (caddr_t)-1) {
 124                 err(0, "%s: %s", fname, strerror(EFBIG));
 125                 return;
 126         }
 127         p = start + size - 1;
 128
 129         if (style == RBYTES && off < size)
 130                 size = off;
 131
 132         /* Last char is special, ignore whether newline or not. */
 133         for (llen = 1; --size; ++llen)
 134                 if (*--p == '\n') {
 135                         WR(p + 1, llen);
 136                         llen = 0;
 137                         if (style == RLINES && !--off) {
 138                                 ++p;
 139                                 break;
 140                         }
 141                 }
 142         if (llen)
 143                 WR(p, llen);
 144         if (munmap(start, (size_t)sbp->st_size))
 145                 err(0, "%s: %s", fname, strerror(errno));
 146 }
 147
 148 typedef struct bf {
 149         struct bf *next;
 150         struct bf *prev;
 151         int len;
 152         char *l;
 153 } BF;
 154
 155 /*
 156  * r_buf -- display a non-regular file in reverse order by line.
 157  *
 158  * This is the function that saves the entire input, storing the data in a
 159  * doubly linked list of buffers and then displays them in reverse order.
 160  * It has the usual nastiness of trying to find the newlines, as there's no
 161  * guarantee that a newline occurs anywhere in the file, let alone in any
 162  * particular buffer.  If we run out of memory, input is discarded (and the
 163  * user warned).
 164  */
 165 static void
 166 r_buf(FILE *fp)
 167 {
 168         BF *mark, *tl, *tr;
 169         int ch, len, llen;
 170         char *p;
 171         off_t enomem;
 172
 173 #define BSZ     (128 * 1024)
 174         tl =  NULL;
 175         for (mark = NULL, enomem = 0;;) {
 176                 /*
 177                  * Allocate a new block and link it into place in a doubly
 178                  * linked list.  If out of memory, toss the LRU block and
 179                  * keep going.
 180                  */
 181                 if (enomem) {
 182                         if (!mark) {
 183                                 errno = ENOMEM;
 184                                 err(1, NULL);
 185                         }
 186                         tl = tl->next;
 187                         enomem += tl->len;
 188                 } else if ((tl = malloc(sizeof(BF))) == NULL ||
 189                     (tl->l = malloc(BSZ)) == NULL) {
 190                         if (tl)
 191                                 free(tl);
 192                         if (!mark) {
 193                                 errno = ENOMEM;
 194                                 err(1, NULL);
 195                         }
 196                         tl = mark;
 197                         enomem += tl->len;
 198                 } else if (mark) {
 199                         tl->next = mark;
 200                         tl->prev = mark->prev;
 201                         mark->prev->next = tl;
 202                         mark->prev = tl;
 203                 } else {
 204                         mark = tl;
 205                         mark->next = mark->prev = mark;
 206                 }
 207
 208                 /* Fill the block with input data. */
 209                 ch = 0;
 210                 for (p = tl->l, len = 0;
 211                     len < BSZ && (ch = getc(fp)) != EOF; ++len)
 212                         *p++ = ch;
 213
 214                 /*
 215                  * If no input data for this block and we tossed some data,
 216                  * recover it.
 217                  */
 218                 if (!len) {
 219                         if (enomem)
 220                                 enomem -= tl->len;
 221                         tl = tl->prev;
 222                         break;
 223                 }
 224
 225                 tl->len = len;
 226                 if (ch == EOF)
 227                         break;
 228         }
 229
 230         if (enomem) {
 231                 (void)fprintf(stderr,
 232                     "tail: warning: %lld bytes discarded\n", (long long)enomem);
 233                 rval = 1;
 234         }
 235
 236         /*
 237          * Step through the blocks in the reverse order read.  The last char
 238          * is special, ignore whether newline or not.
 239          */
 240         for (mark = tl;;) {
 241                 for (p = tl->l + (len = tl->len) - 1, llen = 0; len--;
 242                     --p, ++llen)
 243                         if (*p == '\n') {
 244                                 if (llen) {
 245                                         WR(p + 1, llen);
 246                                         llen = 0;
 247                                 }
 248                                 if (tl == mark)
 249                                         continue;
 250                                 for (tr = tl->next; tr->len; tr = tr->next) {
 251                                         WR(tr->l, tr->len);
 252                                         tr->len = 0;
 253                                         if (tr == mark)
 254                                                 break;
 255                                 }
 256                         }
 257                 tl->len = llen;
 258                 if ((tl = tl->prev) == mark)
 259                         break;
 260         }
 261         tl = tl->next;
 262         if (tl->len) {
 263                 WR(tl->l, tl->len);
 264                 tl->len = 0;
 265         }
 266         while ((tl = tl->next)->len) {
 267                 WR(tl->l, tl->len);
 268                 tl->len = 0;
 269         }
 270 }