1/* vi: set sw=4 ts=4: */
2/*
3 * circular buffer syslog implementation for busybox
4 *
5 * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
6 *
7 * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
8 *
9 * Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
10 */
11
12#include "libbb.h"
13#include <sys/ipc.h>
14#include <sys/sem.h>
15#include <sys/shm.h>
16
17#define DEBUG 0
18
19enum { KEY_ID = 0x414e4547 }; /* "GENA" */
20
21static struct shbuf_ds {
22	int32_t size;           // size of data - 1
23	int32_t tail;           // end of message list
24	char data[1];           // messages
25} *shbuf;
26
27// Semaphore operation structures
28static struct sembuf SMrup[1] = {{0, -1, IPC_NOWAIT | SEM_UNDO}}; // set SMrup
29static struct sembuf SMrdn[2] = {{1, 0}, {0, +1, SEM_UNDO}}; // set SMrdn
30
31
32static void error_exit(const char *str) ATTRIBUTE_NORETURN;
33static void error_exit(const char *str)
34{
35	//release all acquired resources
36	shmdt(shbuf);
37	bb_perror_msg_and_die(str);
38}
39
40/*
41 * sem_up - up()'s a semaphore.
42 */
43static void sem_up(int semid)
44{
45	if (semop(semid, SMrup, 1) == -1)
46		error_exit("semop[SMrup]");
47}
48
49static void interrupted(int sig ATTRIBUTE_UNUSED)
50{
51	signal(SIGINT, SIG_IGN);
52	shmdt(shbuf);
53	exit(0);
54}
55
56int logread_main(int argc, char **argv);
57int logread_main(int argc, char **argv)
58{
59	int cur;
60	int log_semid; /* ipc semaphore id */
61	int log_shmid; /* ipc shared memory id */
62	smallint follow = getopt32(argv, "f");
63
64	log_shmid = shmget(KEY_ID, 0, 0);
65	if (log_shmid == -1)
66		bb_perror_msg_and_die("can't find syslogd buffer");
67
68	/* Attach shared memory to our char* */
69	shbuf = shmat(log_shmid, NULL, SHM_RDONLY);
70	if (shbuf == NULL)
71		bb_perror_msg_and_die("can't access syslogd buffer");
72
73	log_semid = semget(KEY_ID, 0, 0);
74	if (log_semid == -1)
75		error_exit("can't get access to semaphores for syslogd buffer");
76
77	signal(SIGINT, interrupted);
78
79	/* Suppose atomic memory read */
80	/* Max possible value for tail is shbuf->size - 1 */
81	cur = shbuf->tail;
82
83	/* Loop for logread -f, one pass if there was no -f */
84	do {
85		unsigned shbuf_size;
86		unsigned shbuf_tail;
87		const char *shbuf_data;
88#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
89		int i;
90		int len_first_part;
91		int len_total = len_total; /* for gcc */
92		char *copy = copy; /* for gcc */
93#endif
94		if (semop(log_semid, SMrdn, 2) == -1)
95			error_exit("semop[SMrdn]");
96
97		/* Copy the info, helps gcc to realize that it doesn't change */
98		shbuf_size = shbuf->size;
99		shbuf_tail = shbuf->tail;
100		shbuf_data = shbuf->data; /* pointer! */
101
102		if (DEBUG)
103			printf("cur:%d tail:%i size:%i\n",
104					cur, shbuf_tail, shbuf_size);
105
106		if (!follow) {
107			/* advance to oldest complete message */
108			/* find NUL */
109			cur += strlen(shbuf_data + cur);
110			if (cur >= shbuf_size) { /* last byte in buffer? */
111				cur = strnlen(shbuf_data, shbuf_tail);
112				if (cur == shbuf_tail)
113					goto unlock; /* no complete messages */
114			}
115			/* advance to first byte of the message */
116			cur++;
117			if (cur >= shbuf_size) /* last byte in buffer? */
118				cur = 0;
119		} else { /* logread -f */
120			if (cur == shbuf_tail) {
121				sem_up(log_semid);
122				fflush(stdout);
123				sleep(1); /* TODO: replace me with a sleep_on */
124				continue;
125			}
126		}
127
128		/* Read from cur to tail */
129#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
130		len_first_part = len_total = shbuf_tail - cur;
131		if (len_total < 0) {
132			/* message wraps: */
133			/* [SECOND PART.........FIRST PART] */
134			/*  ^data      ^tail    ^cur      ^size */
135			len_total += shbuf_size;
136		}
137		copy = xmalloc(len_total + 1);
138		if (len_first_part < 0) {
139			/* message wraps (see above) */
140			len_first_part = shbuf_size - cur;
141			memcpy(copy + len_first_part, shbuf_data, shbuf_tail);
142		}
143		memcpy(copy, shbuf_data + cur, len_first_part);
144		copy[len_total] = '\0';
145		cur = shbuf_tail;
146#else
147		while (cur != shbuf_tail) {
148			fputs(shbuf_data + cur, stdout);
149			cur += strlen(shbuf_data + cur) + 1;
150			if (cur >= shbuf_size)
151				cur = 0;
152		}
153#endif
154 unlock:
155		/* release the lock on the log chain */
156		sem_up(log_semid);
157
158#if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING
159		for (i = 0; i < len_total; i += strlen(copy + i) + 1) {
160			fputs(copy + i, stdout);
161		}
162		free(copy);
163#endif
164	} while (follow);
165
166	shmdt(shbuf);
167
168	fflush_stdout_and_exit(EXIT_SUCCESS);
169}
170