busybox/sysklogd/klogd.c
James Byrne 6937487be7 libbb: reduce the overhead of single parameter bb_error_msg() calls
Back in 2007, commit 0c97c9d437 ("'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>
2019-07-02 11:35:03 +02:00

303 lines
8.2 KiB
C

/* vi: set sw=4 ts=4: */
/*
* Mini klogd implementation for busybox
*
* Copyright (C) 2001 by Gennady Feldman <gfeldman@gena01.com>.
* Changes: Made this a standalone busybox module which uses standalone
* syslog() client interface.
*
* Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
*
* Copyright (C) 2000 by Karl M. Hegbloom <karlheg@debian.org>
*
* "circular buffer" 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 KLOGD
//config: bool "klogd (5.7 kb)"
//config: default y
//config: help
//config: klogd is a utility which intercepts and logs all
//config: messages from the Linux kernel and sends the messages
//config: out to the 'syslogd' utility so they can be logged. If
//config: you wish to record the messages produced by the kernel,
//config: you should enable this option.
//config:
//config:comment "klogd should not be used together with syslog to kernel printk buffer"
//config: depends on KLOGD && FEATURE_KMSG_SYSLOG
//config:
//config:config FEATURE_KLOGD_KLOGCTL
//config: bool "Use the klogctl() interface"
//config: default y
//config: depends on KLOGD
//config: select PLATFORM_LINUX
//config: help
//config: The klogd applet supports two interfaces for reading
//config: kernel messages. Linux provides the klogctl() interface
//config: which allows reading messages from the kernel ring buffer
//config: independently from the file system.
//config:
//config: If you answer 'N' here, klogd will use the more portable
//config: approach of reading them from /proc or a device node.
//config: However, this method requires the file to be available.
//config:
//config: If in doubt, say 'Y'.
//applet:IF_KLOGD(APPLET(klogd, BB_DIR_SBIN, BB_SUID_DROP))
//kbuild:lib-$(CONFIG_KLOGD) += klogd.o
//usage:#define klogd_trivial_usage
//usage: "[-c N] [-n]"
//usage:#define klogd_full_usage "\n\n"
//usage: "Log kernel messages to syslog\n"
//usage: "\n -c N Print to console messages more urgent than prio N (1-8)"
//usage: "\n -n Run in foreground"
#include "libbb.h"
#include "common_bufsiz.h"
#include <syslog.h>
/* The Linux-specific klogctl(3) interface does not rely on the filesystem and
* allows us to change the console loglevel. Alternatively, we read the
* messages from _PATH_KLOG. */
#if ENABLE_FEATURE_KLOGD_KLOGCTL
# include <sys/klog.h>
static void klogd_open(void)
{
/* "Open the log. Currently a NOP" */
klogctl(1, NULL, 0);
}
static void klogd_setloglevel(int lvl)
{
/* "printk() prints a message on the console only if it has a loglevel
* less than console_loglevel". Here we set console_loglevel = lvl. */
klogctl(8, NULL, lvl);
}
static int klogd_read(char *bufp, int len)
{
/* "2 -- Read from the log." */
return klogctl(2, bufp, len);
}
# define READ_ERROR "klogctl(2) error"
static void klogd_close(void)
{
/* FYI: cmd 7 is equivalent to setting console_loglevel to 7
* via klogctl(8, NULL, 7). */
klogctl(7, NULL, 0); /* "7 -- Enable printk's to console" */
klogctl(0, NULL, 0); /* "0 -- Close the log. Currently a NOP" */
}
#else
# ifndef _PATH_KLOG
# ifdef __GNU__
# define _PATH_KLOG "/dev/klog"
# else
# error "your system's _PATH_KLOG is unknown"
# endif
# endif
# define PATH_PRINTK "/proc/sys/kernel/printk"
enum { klogfd = 3 };
static void klogd_open(void)
{
int fd = xopen(_PATH_KLOG, O_RDONLY);
xmove_fd(fd, klogfd);
}
static void klogd_setloglevel(int lvl)
{
FILE *fp = fopen_or_warn(PATH_PRINTK, "w");
if (fp) {
/* This changes only first value:
* "messages with a higher priority than this
* [that is, with numerically lower value]
* will be printed to the console".
* The other three values in this pseudo-file aren't changed.
*/
fprintf(fp, "%u\n", lvl);
fclose(fp);
}
}
static int klogd_read(char *bufp, int len)
{
return read(klogfd, bufp, len);
}
# define READ_ERROR "read error"
static void klogd_close(void)
{
klogd_setloglevel(7);
if (ENABLE_FEATURE_CLEAN_UP)
close(klogfd);
}
#endif
#define log_buffer bb_common_bufsiz1
enum {
KLOGD_LOGBUF_SIZE = COMMON_BUFSIZE,
OPT_LEVEL = (1 << 0),
OPT_FOREGROUND = (1 << 1),
};
/* TODO: glibc openlog(LOG_KERN) reverts to LOG_USER instead,
* because that's how they interpret word "default"
* in the openlog() manpage:
* LOG_USER (default)
* generic user-level messages
* and the fact that LOG_KERN is a constant 0.
* glibc interprets it as "0 in openlog() call means 'use default'".
* I think it means "if openlog wasn't called before syslog() is called,
* use default".
* Convincing glibc maintainers otherwise is, as usual, nearly impossible.
* Should we open-code syslog() here to use correct facility?
*/
int klogd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int klogd_main(int argc UNUSED_PARAM, char **argv)
{
int i = 0;
char *opt_c;
int opt;
int used;
setup_common_bufsiz();
opt = getopt32(argv, "c:n", &opt_c);
if (opt & OPT_LEVEL) {
/* Valid levels are between 1 and 8 */
i = xatou_range(opt_c, 1, 8);
}
if (!(opt & OPT_FOREGROUND)) {
bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
}
logmode = LOGMODE_SYSLOG;
/* klogd_open() before openlog(), since it might use fixed fd 3,
* and openlog() also may use the same fd 3 if we swap them:
*/
klogd_open();
openlog("kernel", 0, LOG_KERN);
/*
* glibc problem: for some reason, glibc changes LOG_KERN to LOG_USER
* above. The logic behind this is that standard
* http://pubs.opengroup.org/onlinepubs/9699919799/functions/syslog.html
* says the following about openlog and syslog:
* "LOG_USER
* Messages generated by arbitrary processes.
* This is the default facility identifier if none is specified."
*
* I believe glibc misinterpreted this text as "if openlog's
* third parameter is 0 (=LOG_KERN), treat it as LOG_USER".
* Whereas it was meant to say "if *syslog* is called with facility
* 0 in its 1st parameter without prior call to openlog, then perform
* implicit openlog(LOG_USER)".
*
* As a result of this, eh, feature, standard klogd was forced
* to open-code its own openlog and syslog implementation (!).
*
* Note that prohibiting openlog(LOG_KERN) on libc level does not
* add any security: any process can open a socket to "/dev/log"
* and write a string "<0>Voila, a LOG_KERN + LOG_EMERG message"
*
* Google code search tells me there is no widespread use of
* openlog("foo", 0, 0), thus fixing glibc won't break userspace.
*
* The bug against glibc was filed:
* bugzilla.redhat.com/show_bug.cgi?id=547000
*/
if (i)
klogd_setloglevel(i);
signal(SIGHUP, SIG_IGN);
/* We want klogd_read to not be restarted, thus _norestart: */
bb_signals_recursive_norestart(BB_FATAL_SIGS, record_signo);
syslog(LOG_NOTICE, "klogd started: %s", bb_banner);
write_pidfile_std_path_and_ext("klogd");
used = 0;
while (!bb_got_signal) {
int n;
int priority;
char *start;
start = log_buffer + used;
n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
if (n < 0) {
if (errno == EINTR)
continue;
bb_simple_perror_msg(READ_ERROR);
break;
}
start[n] = '\0';
/* Process each newline-terminated line in the buffer */
start = log_buffer;
while (1) {
char *newline = strchrnul(start, '\n');
if (*newline == '\0') {
/* This line is incomplete */
/* move it to the front of the buffer */
overlapping_strcpy(log_buffer, start);
used = newline - start;
if (used < KLOGD_LOGBUF_SIZE-1) {
/* buffer isn't full */
break;
}
/* buffer is full, log it anyway */
used = 0;
newline = NULL;
} else {
*newline++ = '\0';
}
/* Extract the priority */
priority = LOG_INFO;
if (*start == '<') {
start++;
if (*start) {
char *end;
priority = strtoul(start, &end, 10);
if (*end == '>')
end++;
start = end;
}
}
/* Log (only non-empty lines) */
if (*start)
syslog(priority, "%s", start);
if (!newline)
break;
start = newline;
}
}
klogd_close();
syslog(LOG_NOTICE, "klogd: exiting");
remove_pidfile_std_path_and_ext("klogd");
if (bb_got_signal)
kill_myself_with_sig(bb_got_signal);
return EXIT_FAILURE;
}