/* vi: set sw=4 ts=4: */ /* * circular buffer syslog implementation for busybox * * Copyright (C) 2000 by Gennady Feldman * * Maintainer: Gennady Feldman as of Mar 12, 2001 * * Licensed under GPLv2 or later, see file LICENSE in this source tree. */ //config:config LOGREAD //config: bool "logread (4.8 kb)" //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 #include #include #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_simple_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(); sleep1(); /* 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_stdout(shbuf_data + cur); 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_stdout(copy + i); } free(copy); #endif fflush_all(); } while (follow); /* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */ fflush_stdout_and_exit(EXIT_SUCCESS); }