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63c2e7ecc

Jeremie Koenig
Jeremie Koenig
2010-08-01
FAILED Duration: 40s

Subject

klogd: make it work on non-linux systems

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Architecture & Compiler Flags

Architecture: x86_64-linux-gnu Compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04.3) 11.4.0

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Commit Diff GitHub →

sysklogd/Config.src +16 -1sysklogd/klogd.c +110 -18
sysklogd/Config.src+16 -1
@@ -109,7 +109,6 @@ config FEATURE_LOGREAD_REDUCED_LOCKING
config KLOGD
bool "klogd"
default y
- depends on PLATFORM_LINUX
help
klogd is a utility which intercepts and logs all
messages from the Linux kernel and sends the messages
@@ -117,6 +116,22 @@ config KLOGD
you wish to record the messages produced by the kernel,
you should enable this option.
+config FEATURE_KLOGD_KLOGCTL
+ bool "Use the klogctl() interface"
+ default y
+ depends on KLOGD && PLATFORM_LINUX
+ help
+ The klogd applet supports two interfaces for reading
+ kernel messages. Linux provides the klogctl() interface
+ which allows reading messages from the kernel ring buffer
+ independently from the file system.
+
+ If you answer 'N' here, klogd will use the more portable
+ approach of reading them from /proc or a device node.
+ However, this method requires the file to be available.
+
+ If in doubt, say 'Y'.
+
config LOGGER
bool "logger"
default y
sysklogd/klogd.c+110 -18
@@ -4,7 +4,7 @@
*
* Copyright (C) 2001 by Gennady Feldman <[email protected]>.
* Changes: Made this a standalone busybox module which uses standalone
- * syslog() client interface.
+ * syslog() client interface.
*
* Copyright (C) 1999-2004 by Erik Andersen <[email protected]>
*
@@ -19,18 +19,93 @@
#include "libbb.h"
#include <syslog.h>
-#include <sys/klog.h>
-static void klogd_signal(int sig)
+
+/* 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)
+{
+ 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" */
- syslog(LOG_NOTICE, "klogd: exiting");
- kill_myself_with_sig(sig);
}
+#else
+
+# include <paths.h>
+# 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 = sizeof(log_buffer),
@@ -38,6 +113,19 @@ enum {
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)
{
@@ -55,34 +143,34 @@ int klogd_main(int argc UNUSED_PARAM, char **argv)
bb_daemonize_or_rexec(DAEMON_CHDIR_ROOT, argv);
}
- openlog("kernel", 0, LOG_KERN);
-
- bb_signals(BB_FATAL_SIGS, klogd_signal);
- signal(SIGHUP, SIG_IGN);
+ logmode = LOGMODE_SYSLOG;
- /* "Open the log. Currently a NOP" */
- klogctl(1, NULL, 0);
+ /* 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);
- /* "printk() prints a message on the console only if it has a loglevel
- * less than console_loglevel". Here we set console_loglevel = i. */
if (i)
- klogctl(8, NULL, i);
+ klogd_setloglevel(i);
+
+ bb_signals(BB_FATAL_SIGS, record_signo);
+ signal(SIGHUP, SIG_IGN);
syslog(LOG_NOTICE, "klogd started: %s", bb_banner);
- while (1) {
+ while (!bb_got_signal) {
int n;
int priority;
char *start;
/* "2 -- Read from the log." */
start = log_buffer + used;
- n = klogctl(2, start, KLOGD_LOGBUF_SIZE-1 - used);
+ n = klogd_read(start, KLOGD_LOGBUF_SIZE-1 - used);
if (n < 0) {
if (errno == EINTR)
continue;
- syslog(LOG_ERR, "klogd: error %d in klogctl(2): %m",
- errno);
+ bb_perror_msg(READ_ERROR);
break;
}
start[n] = '\0';
@@ -131,5 +219,9 @@ int klogd_main(int argc UNUSED_PARAM, char **argv)
}
}
+ klogd_close();
+ syslog(LOG_NOTICE, "klogd: exiting");
+ if (bb_got_signal)
+ kill_myself_with_sig(bb_got_signal);
return EXIT_FAILURE;
}