| /* vi: set sw=4 ts=4: */ |
| /* |
| * circular buffer syslog implementation for busybox |
| * |
| * Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com> |
| * |
| * Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001 |
| * |
| * Licensed under GPLv2 or later, see file LICENSE in this source tree. |
| */ |
| //config:config LOGREAD |
| //config: bool "logread" |
| //config: default y |
| //WRONG: it should be compilable without SYSLOG=y: |
| //WRONG: depends on FEATURE_IPC_SYSLOG |
| //config: help |
| //config: If you enabled Circular Buffer support, you almost |
| //config: certainly want to enable this feature as well. This |
| //config: utility will allow you to read the messages that are |
| //config: stored in the syslogd circular buffer. |
| //config: |
| //config:config FEATURE_LOGREAD_REDUCED_LOCKING |
| //config: bool "Double buffering" |
| //config: default y |
| //config: depends on LOGREAD |
| //config: help |
| //config: 'logread' output to slow serial terminals can have |
| //config: side effects on syslog because of the semaphore. |
| //config: This option make logread to double buffer copy |
| //config: from circular buffer, minimizing semaphore |
| //config: contention at some minor memory expense. |
| //config: |
| |
| //applet:IF_LOGREAD(APPLET(logread, BB_DIR_SBIN, BB_SUID_DROP)) |
| |
| //kbuild:lib-$(CONFIG_LOGREAD) += logread.o |
| |
| //usage:#define logread_trivial_usage |
| //usage: "[-fF]" |
| //usage:#define logread_full_usage "\n\n" |
| //usage: "Show messages in syslogd's circular buffer\n" |
| //usage: "\n -f Output data as log grows" |
| //usage: "\n -F Same as -f, but dump buffer first" |
| |
| #include "libbb.h" |
| #include "common_bufsiz.h" |
| #include <sys/ipc.h> |
| #include <sys/sem.h> |
| #include <sys/shm.h> |
| |
| #define DEBUG 0 |
| |
| /* our shared key (syslogd.c and logread.c must be in sync) */ |
| enum { KEY_ID = 0x414e4547 }; /* "GENA" */ |
| |
| struct shbuf_ds { |
| int32_t size; // size of data - 1 |
| int32_t tail; // end of message list |
| char data[1]; // messages |
| }; |
| |
| static const struct sembuf init_sem[3] = { |
| {0, -1, IPC_NOWAIT | SEM_UNDO}, |
| {1, 0}, {0, +1, SEM_UNDO} |
| }; |
| |
| struct globals { |
| struct sembuf SMrup[1]; // {0, -1, IPC_NOWAIT | SEM_UNDO}, |
| struct sembuf SMrdn[2]; // {1, 0}, {0, +1, SEM_UNDO} |
| struct shbuf_ds *shbuf; |
| } FIX_ALIASING; |
| #define G (*(struct globals*)bb_common_bufsiz1) |
| #define SMrup (G.SMrup) |
| #define SMrdn (G.SMrdn) |
| #define shbuf (G.shbuf) |
| #define INIT_G() do { \ |
| setup_common_bufsiz(); \ |
| memcpy(SMrup, init_sem, sizeof(init_sem)); \ |
| } while (0) |
| |
| #if 0 |
| static void error_exit(const char *str) NORETURN; |
| static void error_exit(const char *str) |
| { |
| /* Release all acquired resources */ |
| shmdt(shbuf); |
| bb_perror_msg_and_die(str); |
| } |
| #else |
| /* On Linux, shmdt is not mandatory on exit */ |
| # define error_exit(str) bb_perror_msg_and_die(str) |
| #endif |
| |
| /* |
| * sem_up - up()'s a semaphore. |
| */ |
| static void sem_up(int semid) |
| { |
| if (semop(semid, SMrup, 1) == -1) |
| error_exit("semop[SMrup]"); |
| } |
| |
| static void interrupted(int sig) |
| { |
| /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */ |
| kill_myself_with_sig(sig); |
| } |
| |
| int logread_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; |
| int logread_main(int argc UNUSED_PARAM, char **argv) |
| { |
| unsigned cur; |
| int log_semid; /* ipc semaphore id */ |
| int log_shmid; /* ipc shared memory id */ |
| int follow = getopt32(argv, "fF"); |
| |
| INIT_G(); |
| |
| log_shmid = shmget(KEY_ID, 0, 0); |
| if (log_shmid == -1) |
| bb_perror_msg_and_die("can't %s syslogd buffer", "find"); |
| |
| /* Attach shared memory to our char* */ |
| shbuf = shmat(log_shmid, NULL, SHM_RDONLY); |
| if (shbuf == NULL) |
| bb_perror_msg_and_die("can't %s syslogd buffer", "access"); |
| |
| log_semid = semget(KEY_ID, 0, 0); |
| if (log_semid == -1) |
| error_exit("can't get access to semaphores for syslogd buffer"); |
| |
| bb_signals(BB_FATAL_SIGS, interrupted); |
| |
| /* Suppose atomic memory read */ |
| /* Max possible value for tail is shbuf->size - 1 */ |
| cur = shbuf->tail; |
| |
| /* Loop for -f or -F, one pass otherwise */ |
| do { |
| unsigned shbuf_size; |
| unsigned shbuf_tail; |
| const char *shbuf_data; |
| #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
| int i; |
| int len_first_part; |
| int len_total = len_total; /* for gcc */ |
| char *copy = copy; /* for gcc */ |
| #endif |
| if (semop(log_semid, SMrdn, 2) == -1) |
| error_exit("semop[SMrdn]"); |
| |
| /* Copy the info, helps gcc to realize that it doesn't change */ |
| shbuf_size = shbuf->size; |
| shbuf_tail = shbuf->tail; |
| shbuf_data = shbuf->data; /* pointer! */ |
| |
| if (DEBUG) |
| printf("cur:%u tail:%u size:%u\n", |
| cur, shbuf_tail, shbuf_size); |
| |
| if (!(follow & 1)) { /* not -f */ |
| /* if -F, "convert" it to -f, so that we don't |
| * dump the entire buffer on each iteration |
| */ |
| follow >>= 1; |
| |
| /* advance to oldest complete message */ |
| /* find NUL */ |
| cur += strlen(shbuf_data + cur); |
| if (cur >= shbuf_size) { /* last byte in buffer? */ |
| cur = strnlen(shbuf_data, shbuf_tail); |
| if (cur == shbuf_tail) |
| goto unlock; /* no complete messages */ |
| } |
| /* advance to first byte of the message */ |
| cur++; |
| if (cur >= shbuf_size) /* last byte in buffer? */ |
| cur = 0; |
| } else { /* -f */ |
| if (cur == shbuf_tail) { |
| sem_up(log_semid); |
| fflush_all(); |
| sleep(1); /* TODO: replace me with a sleep_on */ |
| continue; |
| } |
| } |
| |
| /* Read from cur to tail */ |
| #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
| len_first_part = len_total = shbuf_tail - cur; |
| if (len_total < 0) { |
| /* message wraps: */ |
| /* [SECOND PART.........FIRST PART] */ |
| /* ^data ^tail ^cur ^size */ |
| len_total += shbuf_size; |
| } |
| copy = xmalloc(len_total + 1); |
| if (len_first_part < 0) { |
| /* message wraps (see above) */ |
| len_first_part = shbuf_size - cur; |
| memcpy(copy + len_first_part, shbuf_data, shbuf_tail); |
| } |
| memcpy(copy, shbuf_data + cur, len_first_part); |
| copy[len_total] = '\0'; |
| cur = shbuf_tail; |
| #else |
| while (cur != shbuf_tail) { |
| fputs(shbuf_data + cur, stdout); |
| cur += strlen(shbuf_data + cur) + 1; |
| if (cur >= shbuf_size) |
| cur = 0; |
| } |
| #endif |
| unlock: |
| /* release the lock on the log chain */ |
| sem_up(log_semid); |
| |
| #if ENABLE_FEATURE_LOGREAD_REDUCED_LOCKING |
| for (i = 0; i < len_total; i += strlen(copy + i) + 1) { |
| fputs(copy + i, stdout); |
| } |
| free(copy); |
| #endif |
| fflush_all(); |
| } while (follow); |
| |
| /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */ |
| |
| fflush_stdout_and_exit(EXIT_SUCCESS); |
| } |