reverse.c revision 314425 
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 * 4. Neither the name of the University nor the names of its contributors
17 *    may be used to endorse or promote products derived from this software
18 *    without specific prior written permission.
19 *
20 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
21 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
22 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
23 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
24 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
25 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
26 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
27 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
28 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
29 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
30 * SUCH DAMAGE.
31 */
32
33#if 0
34#ifndef lint
35static char sccsid[] = "@(#)reverse.c	8.1 (Berkeley) 6/6/93";
36#endif /* not lint */
37#endif
38
39#include <sys/cdefs.h>
40__FBSDID("$FreeBSD: stable/10/usr.bin/tail/reverse.c 314425 2017-02-28 22:18:05Z asomers $");
41
42#include <sys/param.h>
43#include <sys/queue.h>
44#include <sys/stat.h>
45#include <sys/mman.h>
46
47#include <err.h>
48#include <errno.h>
49#include <limits.h>
50#include <stdint.h>
51#include <stdio.h>
52#include <stdlib.h>
53#include <string.h>
54#include <unistd.h>
55
56#include "extern.h"
57
58static void r_buf(FILE *, const char *);
59static void r_reg(FILE *, const char *, enum STYLE, off_t, struct stat *);
60
61/*
62 * reverse -- display input in reverse order by line.
63 *
64 * There are six separate cases for this -- regular and non-regular
65 * files by bytes, lines or the whole file.
66 *
67 * BYTES	display N bytes
68 *	REG	mmap the file and display the lines
69 *	NOREG	cyclically read characters into a wrap-around buffer
70 *
71 * LINES	display N lines
72 *	REG	mmap the file and display the lines
73 *	NOREG	cyclically read lines into a wrap-around array of buffers
74 *
75 * FILE		display the entire file
76 *	REG	mmap the file and display the lines
77 *	NOREG	cyclically read input into a linked list of buffers
78 */
79void
80reverse(FILE *fp, const char *fn, enum STYLE style, off_t off, struct stat *sbp)
81{
82	if (style != REVERSE && off == 0)
83		return;
84
85	if (S_ISREG(sbp->st_mode))
86		r_reg(fp, fn, style, off, sbp);
87	else
88		switch(style) {
89		case FBYTES:
90		case RBYTES:
91			bytes(fp, fn, off);
92			break;
93		case FLINES:
94		case RLINES:
95			lines(fp, fn, off);
96			break;
97		case REVERSE:
98			r_buf(fp, fn);
99			break;
100		default:
101			break;
102		}
103}
104
105/*
106 * r_reg -- display a regular file in reverse order by line.
107 */
108static void
109r_reg(FILE *fp, const char *fn, enum STYLE style, off_t off, struct stat *sbp)
110{
111	struct mapinfo map;
112	off_t curoff, size, lineend;
113	int i;
114
115	if (!(size = sbp->st_size))
116		return;
117
118	map.start = NULL;
119	map.mapoff = map.maxoff = size;
120	map.fd = fileno(fp);
121	map.maplen = 0;
122
123	/*
124	 * Last char is special, ignore whether newline or not. Note that
125	 * size == 0 is dealt with above, and size == 1 sets curoff to -1.
126	 */
127	curoff = size - 2;
128	lineend = size;
129	while (curoff >= 0) {
130		if (curoff < map.mapoff ||
131		    curoff >= map.mapoff + (off_t)map.maplen) {
132			if (maparound(&map, curoff) != 0) {
133				ierr(fn);
134				return;
135			}
136		}
137		for (i = curoff - map.mapoff; i >= 0; i--) {
138			if (style == RBYTES && --off == 0)
139				break;
140			if (map.start[i] == '\n')
141				break;
142		}
143		/* `i' is either the map offset of a '\n', or -1. */
144		curoff = map.mapoff + i;
145		if (i < 0)
146			continue;
147
148		/* Print the line and update offsets. */
149		if (mapprint(&map, curoff + 1, lineend - curoff - 1) != 0) {
150			ierr(fn);
151			return;
152		}
153		lineend = curoff + 1;
154		curoff--;
155
156		if (style == RLINES)
157			off--;
158
159		if (off == 0 && style != REVERSE) {
160			/* Avoid printing anything below. */
161			curoff = 0;
162			break;
163		}
164	}
165	if (curoff < 0 && mapprint(&map, 0, lineend) != 0) {
166		ierr(fn);
167		return;
168	}
169	if (map.start != NULL && munmap(map.start, map.maplen))
170		ierr(fn);
171}
172
173#define BSZ	(128 * 1024)
174typedef struct bfelem {
175	TAILQ_ENTRY(bfelem) entries;
176	size_t len;
177	char l[BSZ];
178} bfelem_t;
179
180/*
181 * r_buf -- display a non-regular file in reverse order by line.
182 *
183 * This is the function that saves the entire input, storing the data in a
184 * doubly linked list of buffers and then displays them in reverse order.
185 * It has the usual nastiness of trying to find the newlines, as there's no
186 * guarantee that a newline occurs anywhere in the file, let alone in any
187 * particular buffer.  If we run out of memory, input is discarded (and the
188 * user warned).
189 */
190static void
191r_buf(FILE *fp, const char *fn)
192{
193	struct bfelem *tl, *first = NULL;
194	size_t llen;
195	char *p;
196	off_t enomem = 0;
197	TAILQ_HEAD(bfhead, bfelem) head;
198
199	TAILQ_INIT(&head);
200
201	while (!feof(fp)) {
202		size_t len;
203
204		/*
205		 * Allocate a new block and link it into place in a doubly
206		 * linked list.  If out of memory, toss the LRU block and
207		 * keep going.
208		 */
209		while ((tl = malloc(sizeof(bfelem_t))) == NULL) {
210			first = TAILQ_FIRST(&head);
211			if (TAILQ_EMPTY(&head))
212				err(1, "malloc");
213			enomem += first->len;
214			TAILQ_REMOVE(&head, first, entries);
215			free(first);
216		}
217		TAILQ_INSERT_TAIL(&head, tl, entries);
218
219		/* Fill the block with input data. */
220		len = 0;
221		while ((!feof(fp)) && len < BSZ) {
222			p = tl->l + len;
223			len += fread(p, 1, BSZ - len, fp);
224			if (ferror(fp)) {
225				ierr(fn);
226				return;
227			}
228		}
229
230		tl->len = len;
231	}
232
233	if (enomem) {
234		warnx("warning: %jd bytes discarded", (intmax_t)enomem);
235		rval = 1;
236	}
237
238	/*
239	 * Now print the lines in reverse order
240	 * Outline:
241	 *    Scan backward for "\n",
242	 *    print forward to the end of the buffers
243	 *    free any buffers that start after the "\n" just found
244	 *    Loop
245	 */
246	tl = TAILQ_LAST(&head, bfhead);
247	first = TAILQ_FIRST(&head);
248	while (tl != NULL) {
249		struct bfelem *temp;
250
251		for (p = tl->l + tl->len - 1, llen = 0; p >= tl->l;
252		    --p, ++llen) {
253			int start = (tl == first && p == tl->l);
254
255			if ((*p == '\n') || start) {
256				struct bfelem *tr;
257
258				if (start && llen)
259					WR(p, llen + 1);
260				else if (llen)
261					WR(p + 1, llen);
262				tr = TAILQ_NEXT(tl, entries);
263				llen = 0;
264				if (tr != NULL) {
265					TAILQ_FOREACH_FROM_SAFE(tr, &head,
266					    entries, temp) {
267						if (tr->len)
268							WR(&tr->l, tr->len);
269						TAILQ_REMOVE(&head, tr,
270						    entries);
271						free(tr);
272					}
273				}
274			}
275		}
276		tl->len = llen;
277		tl = TAILQ_PREV(tl, bfhead, entries);
278	}
279	TAILQ_REMOVE(&head, first, entries);
280	free(first);
281}
282