busybox/sysklogd/logread.c

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/* vi: set sw=4 ts=4: */
/*
* circular buffer syslog implementation for busybox
*
* Copyright (C) 2000 by Gennady Feldman <gfeldman@gena01.com>
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*
* Maintainer: Gennady Feldman <gfeldman@gena01.com> as of Mar 12, 2001
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*
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
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*/
//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
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//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"
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#include <sys/ipc.h>
#include <sys/sem.h>
#include <sys/shm.h>
#define DEBUG 0
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/* our shared key (syslogd.c and logread.c must be in sync) */
enum { KEY_ID = 0x414e4547 }; /* "GENA" */
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struct shbuf_ds {
int32_t size; // size of data - 1
int32_t tail; // end of message list
char data[1]; // messages
};
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static const struct sembuf init_sem[3] = {
{0, -1, IPC_NOWAIT | SEM_UNDO},
{1, 0}, {0, +1, SEM_UNDO}
};
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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)
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#define INIT_G() do { \
setup_common_bufsiz(); \
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memcpy(SMrup, init_sem, sizeof(init_sem)); \
} while (0)
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#if 0
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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 */
libbb: reduce the overhead of single parameter bb_error_msg() calls Back in 2007, commit 0c97c9d43707 ("'simple' error message functions by Loic Grenie") introduced bb_simple_perror_msg() to allow for a lower overhead call to bb_perror_msg() when only a string was being printed with no parameters. This saves space for some CPU architectures because it avoids the overhead of a call to a variadic function. However there has never been a simple version of bb_error_msg(), and since 2007 many new calls to bb_perror_msg() have been added that only take a single parameter and so could have been using bb_simple_perror_message(). This changeset introduces 'simple' versions of bb_info_msg(), bb_error_msg(), bb_error_msg_and_die(), bb_herror_msg() and bb_herror_msg_and_die(), and replaces all calls that only take a single parameter, or use something like ("%s", arg), with calls to the corresponding 'simple' version. Since it is likely that single parameter calls to the variadic functions may be accidentally reintroduced in the future a new debugging config option WARN_SIMPLE_MSG has been introduced. This uses some macro magic which will cause any such calls to generate a warning, but this is turned off by default to avoid use of the unpleasant macros in normal circumstances. This is a large changeset due to the number of calls that have been replaced. The only files that contain changes other than simple substitution of function calls are libbb.h, libbb/herror_msg.c, libbb/verror_msg.c and libbb/xfuncs_printf.c. In miscutils/devfsd.c, networking/udhcp/common.h and util-linux/mdev.c additonal macros have been added for logging so that single parameter and multiple parameter logging variants exist. The amount of space saved varies considerably by architecture, and was found to be as follows (for 'defconfig' using GCC 7.4): Arm: -92 bytes MIPS: -52 bytes PPC: -1836 bytes x86_64: -938 bytes Note that for the MIPS architecture only an exception had to be made disabling the 'simple' calls for 'udhcp' (in networking/udhcp/common.h) because it made these files larger on MIPS. Signed-off-by: James Byrne <james.byrne@origamienergy.com> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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# define error_exit(str) bb_simple_perror_msg_and_die(str)
#endif
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/*
* sem_up - up()'s a semaphore.
*/
static void sem_up(int semid)
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{
if (semop(semid, SMrup, 1) == -1)
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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;
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int logread_main(int argc UNUSED_PARAM, char **argv)
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{
unsigned cur;
int log_semid; /* ipc semaphore id */
int log_shmid; /* ipc shared memory id */
int follow = getopt32(argv, "fF");
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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");
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bb_signals(BB_FATAL_SIGS, interrupted);
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/* 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(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);
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/* shmdt(shbuf); - on Linux, shmdt is not mandatory on exit */
fflush_stdout_and_exit(EXIT_SUCCESS);
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}