1 files changed, 370 insertions, 110 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index b4d97b54c1ec..f64b8997fc76 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -33,6 +33,12 @@
 #include <linux/bootmem.h>
 #include <linux/syscalls.h>
 #include <linux/kexec.h>
+#include <linux/kdb.h>
+#include <linux/ratelimit.h>
+#include <linux/kmsg_dump.h>
+#include <linux/syslog.h>
+#include <linux/cpu.h>
+#include <linux/notifier.h>
 
 #include <asm/uaccess.h>
 
@@ -73,7 +79,7 @@ EXPORT_SYMBOL(oops_in_progress);
  * provides serialisation for access to the entire console
  * driver system.
  */
-static DECLARE_MUTEX(console_sem);
+static DEFINE_SEMAPHORE(console_sem);
 struct console *console_drivers;
 EXPORT_SYMBOL_GPL(console_drivers);
 
@@ -135,6 +141,7 @@ static char __log_buf[__LOG_BUF_LEN];
 static char *log_buf = __log_buf;
 static int log_buf_len = __LOG_BUF_LEN;
 static unsigned logged_chars; /* Number of chars produced since last read+clear operation */
+static int saved_console_loglevel = -1;
 
 #ifdef CONFIG_KEXEC
 /*
@@ -197,13 +204,12 @@ __setup("log_buf_len=", log_buf_len_setup);
 
 #ifdef CONFIG_BOOT_PRINTK_DELAY
 
-static unsigned int boot_delay; /* msecs delay after each printk during bootup */
-static unsigned long long printk_delay_msec; /* per msec, based on boot_delay */
+static int boot_delay; /* msecs delay after each printk during bootup */
+static unsigned long long loops_per_msec;       /* based on boot_delay */
 
 static int __init boot_delay_setup(char *str)
 {
         unsigned long lpj;
-        unsigned long long loops_per_msec;
 
         lpj = preset_lpj ? preset_lpj : 1000000;        /* some guess */
         loops_per_msec = (unsigned long long)lpj / 1000 * HZ;
@@ -212,10 +218,9 @@ static int __init boot_delay_setup(char *str)
         if (boot_delay > 10 * 1000)
                 boot_delay = 0;
 
-        printk_delay_msec = loops_per_msec;
-        printk(KERN_DEBUG "boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
-                "HZ: %d, printk_delay_msec: %llu\n",
-                boot_delay, preset_lpj, lpj, HZ, printk_delay_msec);
+        pr_debug("boot_delay: %u, preset_lpj: %ld, lpj: %lu, "
+                "HZ: %d, loops_per_msec: %llu\n",
+                boot_delay, preset_lpj, lpj, HZ, loops_per_msec);
         return 1;
 }
 __setup("boot_delay=", boot_delay_setup);
@@ -228,7 +233,7 @@ static void boot_delay_msec(void)
         if (boot_delay == 0 || system_state != SYSTEM_BOOTING)
                 return;
 
-        k = (unsigned long long)printk_delay_msec * boot_delay;
+        k = (unsigned long long)loops_per_msec * boot_delay;
 
         timeout = jiffies + msecs_to_jiffies(boot_delay);
         while (k) {
@@ -250,38 +255,42 @@ static inline void boot_delay_msec(void)
 }
 #endif
 
-/*
- * Commands to do_syslog:
- *
- *      0 -- Close the log.  Currently a NOP.
- *      1 -- Open the log. Currently a NOP.
- *      2 -- Read from the log.
- *      3 -- Read all messages remaining in the ring buffer.
- *      4 -- Read and clear all messages remaining in the ring buffer
- *      5 -- Clear ring buffer.
- *      6 -- Disable printk's to console
- *      7 -- Enable printk's to console
- *      8 -- Set level of messages printed to console
- *      9 -- Return number of unread characters in the log buffer
- *     10 -- Return size of the log buffer
- */
-int do_syslog(int type, char __user *buf, int len)
+#ifdef CONFIG_SECURITY_DMESG_RESTRICT
+int dmesg_restrict = 1;
+#else
+int dmesg_restrict;
+#endif
+
+int do_syslog(int type, char __user *buf, int len, bool from_file)
 {
         unsigned i, j, limit, count;
         int do_clear = 0;
         char c;
         int error = 0;
 
+        /*
+         * If this is from /proc/kmsg we only do the capabilities checks
+         * at open time.
+         */
+        if (type == SYSLOG_ACTION_OPEN || !from_file) {
+                if (dmesg_restrict && !capable(CAP_SYSLOG))
+                        goto warn; /* switch to return -EPERM after 2.6.39 */
+                if ((type != SYSLOG_ACTION_READ_ALL &&
+                     type != SYSLOG_ACTION_SIZE_BUFFER) &&
+                    !capable(CAP_SYSLOG))
+                        goto warn; /* switch to return -EPERM after 2.6.39 */
+        }
+
         error = security_syslog(type);
         if (error)
                 return error;
 
         switch (type) {
-        case 0:         /* Close log */
+        case SYSLOG_ACTION_CLOSE:       /* Close log */
                 break;
-        case 1:         /* Open log */
+        case SYSLOG_ACTION_OPEN:        /* Open log */
                 break;
-        case 2:         /* Read from log */
+        case SYSLOG_ACTION_READ:        /* Read from log */
                 error = -EINVAL;
                 if (!buf || len < 0)
                         goto out;
@@ -312,10 +321,12 @@ int do_syslog(int type, char __user *buf, int len)
                 if (!error)
                         error = i;
                 break;
-        case 4:         /* Read/clear last kernel messages */
+        /* Read/clear last kernel messages */
+        case SYSLOG_ACTION_READ_CLEAR:
                 do_clear = 1;
                 /* FALL THRU */
-        case 3:         /* Read last kernel messages */
+        /* Read last kernel messages */
+        case SYSLOG_ACTION_READ_ALL:
                 error = -EINVAL;
                 if (!buf || len < 0)
                         goto out;
@@ -368,28 +379,41 @@ int do_syslog(int type, char __user *buf, int len)
                         }
                 }
                 break;
-        case 5:         /* Clear ring buffer */
+        /* Clear ring buffer */
+        case SYSLOG_ACTION_CLEAR:
                 logged_chars = 0;
                 break;
-        case 6:         /* Disable logging to console */
+        /* Disable logging to console */
+        case SYSLOG_ACTION_CONSOLE_OFF:
+                if (saved_console_loglevel == -1)
+                        saved_console_loglevel = console_loglevel;
                 console_loglevel = minimum_console_loglevel;
                 break;
-        case 7:         /* Enable logging to console */
-                console_loglevel = default_console_loglevel;
+        /* Enable logging to console */
+        case SYSLOG_ACTION_CONSOLE_ON:
+                if (saved_console_loglevel != -1) {
+                        console_loglevel = saved_console_loglevel;
+                        saved_console_loglevel = -1;
+                }
                 break;
-        case 8:         /* Set level of messages printed to console */
+        /* Set level of messages printed to console */
+        case SYSLOG_ACTION_CONSOLE_LEVEL:
                 error = -EINVAL;
                 if (len < 1 || len > 8)
                         goto out;
                 if (len < minimum_console_loglevel)
                         len = minimum_console_loglevel;
                 console_loglevel = len;
+                /* Implicitly re-enable logging to console */
+                saved_console_loglevel = -1;
                 error = 0;
                 break;
-        case 9:         /* Number of chars in the log buffer */
+        /* Number of chars in the log buffer */
+        case SYSLOG_ACTION_SIZE_UNREAD:
                 error = log_end - log_start;
                 break;
-        case 10:        /* Size of the log buffer */
+        /* Size of the log buffer */
+        case SYSLOG_ACTION_SIZE_BUFFER:
                 error = log_buf_len;
                 break;
         default:
@@ -398,13 +422,35 @@ int do_syslog(int type, char __user *buf, int len)
         }
 out:
         return error;
+warn:
+        /* remove after 2.6.39 */
+        if (capable(CAP_SYS_ADMIN))
+                WARN_ONCE(1, "Attempt to access syslog with CAP_SYS_ADMIN "
+                  "but no CAP_SYSLOG (deprecated and denied).\n");
+        return -EPERM;
 }
 
 SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
 {
-        return do_syslog(type, buf, len);
+        return do_syslog(type, buf, len, SYSLOG_FROM_CALL);
 }
 
+#ifdef  CONFIG_KGDB_KDB
+/* kdb dmesg command needs access to the syslog buffer.  do_syslog()
+ * uses locks so it cannot be used during debugging.  Just tell kdb
+ * where the start and end of the physical and logical logs are.  This
+ * is equivalent to do_syslog(3).
+ */
+void kdb_syslog_data(char *syslog_data[4])
+{
+        syslog_data[0] = log_buf;
+        syslog_data[1] = log_buf + log_buf_len;
+        syslog_data[2] = log_buf + log_end -
+                (logged_chars < log_buf_len ? logged_chars : log_buf_len);
+        syslog_data[3] = log_buf + log_end;
+}
+#endif  /* CONFIG_KGDB_KDB */
+
 /*
  * Call the console drivers on a range of log_buf
  */
@@ -412,7 +458,7 @@ static void __call_console_drivers(unsigned start, unsigned end)
 {
         struct console *con;
 
-        for (con = console_drivers; con; con = con->next) {
+        for_each_console(con) {
                 if ((con->flags & CON_ENABLED) && con->write &&
                                 (cpu_online(smp_processor_id()) ||
                                 (con->flags & CON_ANYTIME)))
@@ -529,7 +575,7 @@ static void zap_locks(void)
         /* If a crash is occurring, make sure we can't deadlock */
         spin_lock_init(&logbuf_lock);
         /* And make sure that we print immediately */
-        init_MUTEX(&console_sem);
+        sema_init(&console_sem, 1);
 }
 
 #if defined(CONFIG_PRINTK_TIME)
@@ -544,7 +590,7 @@ static int have_callable_console(void)
 {
         struct console *con;
 
-        for (con = console_drivers; con; con = con->next)
+        for_each_console(con)
                 if (con->flags & CON_ANYTIME)
                         return 1;
 
@@ -578,6 +624,14 @@ asmlinkage int printk(const char *fmt, ...)
         va_list args;
         int r;
 
+#ifdef CONFIG_KGDB_KDB
+        if (unlikely(kdb_trap_printk)) {
+                va_start(args, fmt);
+                r = vkdb_printf(fmt, args);
+                va_end(args);
+                return r;
+        }
+#endif
         va_start(args, fmt);
         r = vprintk(fmt, args);
         va_end(args);
@@ -612,6 +666,7 @@ static inline int can_use_console(unsigned int cpu)
  * released but interrupts still disabled.
  */
 static int acquire_console_semaphore_for_printk(unsigned int cpu)
+        __releases(&logbuf_lock)
 {
         int retval = 0;
 
@@ -640,6 +695,20 @@ static int recursion_bug;
 static int new_text_line = 1;
 static char printk_buf[1024];
 
+int printk_delay_msec __read_mostly;
+
+static inline void printk_delay(void)
+{
+        if (unlikely(printk_delay_msec)) {
+                int m = printk_delay_msec;
+
+                while (m--) {
+                        mdelay(1);
+                        touch_nmi_watchdog();
+                }
+        }
+}
+
 asmlinkage int vprintk(const char *fmt, va_list args)
 {
         int printed_len = 0;
@@ -649,6 +718,7 @@ asmlinkage int vprintk(const char *fmt, va_list args)
         char *p;
 
         boot_delay_msec();
+        printk_delay();
 
         preempt_disable();
         /* This stops the holder of console_sem just where we want him */
@@ -937,6 +1007,32 @@ void resume_console(void)
 }
 
 /**
+ * console_cpu_notify - print deferred console messages after CPU hotplug
+ * @self: notifier struct
+ * @action: CPU hotplug event
+ * @hcpu: unused
+ *
+ * If printk() is called from a CPU that is not online yet, the messages
+ * will be spooled but will not show up on the console.  This function is
+ * called when a new CPU comes online (or fails to come up), and ensures
+ * that any such output gets printed.
+ */
+static int __cpuinit console_cpu_notify(struct notifier_block *self,
+        unsigned long action, void *hcpu)
+{
+        switch (action) {
+        case CPU_ONLINE:
+        case CPU_DEAD:
+        case CPU_DYING:
+        case CPU_DOWN_FAILED:
+        case CPU_UP_CANCELED:
+                acquire_console_sem();
+                release_console_sem();
+        }
+        return NOTIFY_OK;
+}
+
+/**
  * acquire_console_sem - lock the console system for exclusive use.
  *
  * Acquires a semaphore which guarantees that the caller has
@@ -978,21 +1074,23 @@ static DEFINE_PER_CPU(int, printk_pending);
 
 void printk_tick(void)
 {
-        if (__get_cpu_var(printk_pending)) {
-                __get_cpu_var(printk_pending) = 0;
+        if (__this_cpu_read(printk_pending)) {
+                __this_cpu_write(printk_pending, 0);
                 wake_up_interruptible(&log_wait);
         }
 }
 
 int printk_needs_cpu(int cpu)
 {
-        return per_cpu(printk_pending, cpu);
+        if (cpu_is_offline(cpu))
+                printk_tick();
+        return __this_cpu_read(printk_pending);
 }
 
 void wake_up_klogd(void)
 {
         if (waitqueue_active(&log_wait))
-                __raw_get_cpu_var(printk_pending) = 1;
+                this_cpu_write(printk_pending, 1);
 }
 
 /**
@@ -1060,12 +1158,6 @@ void __sched console_conditional_schedule(void)
 }
 EXPORT_SYMBOL(console_conditional_schedule);
 
-void console_print(const char *s)
-{
-        printk(KERN_EMERG "%s", s);
-}
-EXPORT_SYMBOL(console_print);
-
 void console_unblank(void)
 {
         struct console *c;
@@ -1082,7 +1174,7 @@ void console_unblank(void)
 
         console_locked = 1;
         console_may_schedule = 0;
-        for (c = console_drivers; c != NULL; c = c->next)
+        for_each_console(c)
                 if ((c->flags & CON_ENABLED) && c->unblank)
                         c->unblank();
         release_console_sem();
@@ -1097,7 +1189,7 @@ struct tty_driver *console_device(int *index)
         struct tty_driver *driver = NULL;
 
         acquire_console_sem();
-        for (c = console_drivers; c != NULL; c = c->next) {
+        for_each_console(c) {
                 if (!c->device)
                         continue;
                 driver = c->device(c, index);
@@ -1134,25 +1226,49 @@ EXPORT_SYMBOL(console_start);
  * to register the console printing procedure with printk() and to
  * print any messages that were printed by the kernel before the
  * console driver was initialized.
+ *
+ * This can happen pretty early during the boot process (because of
+ * early_printk) - sometimes before setup_arch() completes - be careful
+ * of what kernel features are used - they may not be initialised yet.
+ *
+ * There are two types of consoles - bootconsoles (early_printk) and
+ * "real" consoles (everything which is not a bootconsole) which are
+ * handled differently.
+ *  - Any number of bootconsoles can be registered at any time.
+ *  - As soon as a "real" console is registered, all bootconsoles
+ *    will be unregistered automatically.
+ *  - Once a "real" console is registered, any attempt to register a
+ *    bootconsoles will be rejected
  */
-void register_console(struct console *console)
+void register_console(struct console *newcon)
 {
         int i;
         unsigned long flags;
-        struct console *bootconsole = NULL;
+        struct console *bcon = NULL;
 
-        if (console_drivers) {
-                if (console->flags & CON_BOOT)
-                        return;
-                if (console_drivers->flags & CON_BOOT)
-                        bootconsole = console_drivers;
+        /*
+         * before we register a new CON_BOOT console, make sure we don't
+         * already have a valid console
+         */
+        if (console_drivers && newcon->flags & CON_BOOT) {
+                /* find the last or real console */
+                for_each_console(bcon) {
+                        if (!(bcon->flags & CON_BOOT)) {
+                                printk(KERN_INFO "Too late to register bootconsole %s%d\n",
+                                        newcon->name, newcon->index);
+                                return;
+                        }
+                }
         }
 
-        if (preferred_console < 0 || bootconsole || !console_drivers)
+        if (console_drivers && console_drivers->flags & CON_BOOT)
+                bcon = console_drivers;
+
+        if (preferred_console < 0 || bcon || !console_drivers)
                 preferred_console = selected_console;
 
-        if (console->early_setup)
-                console->early_setup();
+        if (newcon->early_setup)
+                newcon->early_setup();
 
         /*
          *      See if we want to use this console driver. If we
@@ -1160,13 +1276,13 @@ void register_console(struct console *console)
          *      that registers here.
          */
         if (preferred_console < 0) {
-                if (console->index < 0)
-                        console->index = 0;
-                if (console->setup == NULL ||
-                    console->setup(console, NULL) == 0) {
-                        console->flags |= CON_ENABLED;
-                        if (console->device) {
-                                console->flags |= CON_CONSDEV;
+                if (newcon->index < 0)
+                        newcon->index = 0;
+                if (newcon->setup == NULL ||
+                    newcon->setup(newcon, NULL) == 0) {
+                        newcon->flags |= CON_ENABLED;
+                        if (newcon->device) {
+                                newcon->flags |= CON_CONSDEV;
                                 preferred_console = 0;
                         }
                 }
@@ -1178,64 +1294,62 @@ void register_console(struct console *console)
          */
         for (i = 0; i < MAX_CMDLINECONSOLES && console_cmdline[i].name[0];
                         i++) {
-                if (strcmp(console_cmdline[i].name, console->name) != 0)
+                if (strcmp(console_cmdline[i].name, newcon->name) != 0)
                         continue;
-                if (console->index >= 0 &&
-                    console->index != console_cmdline[i].index)
+                if (newcon->index >= 0 &&
+                    newcon->index != console_cmdline[i].index)
                         continue;
-                if (console->index < 0)
-                        console->index = console_cmdline[i].index;
+                if (newcon->index < 0)
+                        newcon->index = console_cmdline[i].index;
 #ifdef CONFIG_A11Y_BRAILLE_CONSOLE
                 if (console_cmdline[i].brl_options) {
-                        console->flags |= CON_BRL;
-                        braille_register_console(console,
+                        newcon->flags |= CON_BRL;
+                        braille_register_console(newcon,
                                         console_cmdline[i].index,
                                         console_cmdline[i].options,
                                         console_cmdline[i].brl_options);
                         return;
                 }
 #endif
-                if (console->setup &&
-                    console->setup(console, console_cmdline[i].options) != 0)
+                if (newcon->setup &&
+                    newcon->setup(newcon, console_cmdline[i].options) != 0)
                         break;
-                console->flags |= CON_ENABLED;
-                console->index = console_cmdline[i].index;
+                newcon->flags |= CON_ENABLED;
+                newcon->index = console_cmdline[i].index;
                 if (i == selected_console) {
-                        console->flags |= CON_CONSDEV;
+                        newcon->flags |= CON_CONSDEV;
                         preferred_console = selected_console;
                 }
                 break;
         }
 
-        if (!(console->flags & CON_ENABLED))
+        if (!(newcon->flags & CON_ENABLED))
                 return;
 
-        if (bootconsole && (console->flags & CON_CONSDEV)) {
-                printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
-                       bootconsole->name, bootconsole->index,
-                       console->name, console->index);
-                unregister_console(bootconsole);
-                console->flags &= ~CON_PRINTBUFFER;
-        } else {
-                printk(KERN_INFO "console [%s%d] enabled\n",
-                       console->name, console->index);
-        }
+        /*
+         * If we have a bootconsole, and are switching to a real console,
+         * don't print everything out again, since when the boot console, and
+         * the real console are the same physical device, it's annoying to
+         * see the beginning boot messages twice
+         */
+        if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV))
+                newcon->flags &= ~CON_PRINTBUFFER;
 
         /*
          *      Put this console in the list - keep the
          *      preferred driver at the head of the list.
          */
         acquire_console_sem();
-        if ((console->flags & CON_CONSDEV) || console_drivers == NULL) {
-                console->next = console_drivers;
-                console_drivers = console;
-                if (console->next)
-                        console->next->flags &= ~CON_CONSDEV;
+        if ((newcon->flags & CON_CONSDEV) || console_drivers == NULL) {
+                newcon->next = console_drivers;
+                console_drivers = newcon;
+                if (newcon->next)
+                        newcon->next->flags &= ~CON_CONSDEV;
         } else {
-                console->next = console_drivers->next;
-                console_drivers->next = console;
+                newcon->next = console_drivers->next;
+                console_drivers->next = newcon;
         }
-        if (console->flags & CON_PRINTBUFFER) {
+        if (newcon->flags & CON_PRINTBUFFER) {
                 /*
                  * release_console_sem() will print out the buffered messages
                  * for us.
@@ -1245,6 +1359,29 @@ void register_console(struct console *console)
                 spin_unlock_irqrestore(&logbuf_lock, flags);
         }
         release_console_sem();
+        console_sysfs_notify();
+
+        /*
+         * By unregistering the bootconsoles after we enable the real console
+         * we get the "console xxx enabled" message on all the consoles -
+         * boot consoles, real consoles, etc - this is to ensure that end
+         * users know there might be something in the kernel's log buffer that
+         * went to the bootconsole (that they do not see on the real console)
+         */
+        if (bcon && ((newcon->flags & (CON_CONSDEV | CON_BOOT)) == CON_CONSDEV)) {
+                /* we need to iterate through twice, to make sure we print
+                 * everything out, before we unregister the console(s)
+                 */
+                printk(KERN_INFO "console [%s%d] enabled, bootconsole disabled\n",
+                        newcon->name, newcon->index);
+                for_each_console(bcon)
+                        if (bcon->flags & CON_BOOT)
+                                unregister_console(bcon);
+        } else {
+                printk(KERN_INFO "%sconsole [%s%d] enabled\n",
+                        (newcon->flags & CON_BOOT) ? "boot" : "" ,
+                        newcon->name, newcon->index);
+        }
 }
 EXPORT_SYMBOL(register_console);
 
@@ -1281,22 +1418,26 @@ int unregister_console(struct console *console)
                 console_drivers->flags |= CON_CONSDEV;
 
         release_console_sem();
+        console_sysfs_notify();
         return res;
 }
 EXPORT_SYMBOL(unregister_console);
 
-static int __init disable_boot_consoles(void)
+static int __init printk_late_init(void)
 {
-        if (console_drivers != NULL) {
-                if (console_drivers->flags & CON_BOOT) {
+        struct console *con;
+
+        for_each_console(con) {
+                if (con->flags & CON_BOOT) {
                         printk(KERN_INFO "turn off boot console %s%d\n",
-                                console_drivers->name, console_drivers->index);
-                        return unregister_console(console_drivers);
+                                con->name, con->index);
+                        unregister_console(con);
                 }
         }
+        hotcpu_notifier(console_cpu_notify, 0);
         return 0;
 }
-late_initcall(disable_boot_consoles);
+late_initcall(printk_late_init);
 
 #if defined CONFIG_PRINTK
 
@@ -1308,11 +1449,11 @@ late_initcall(disable_boot_consoles);
  */
 DEFINE_RATELIMIT_STATE(printk_ratelimit_state, 5 * HZ, 10);
 
-int printk_ratelimit(void)
+int __printk_ratelimit(const char *func)
 {
-        return __ratelimit(&printk_ratelimit_state);
+        return ___ratelimit(&printk_ratelimit_state, func);
 }
-EXPORT_SYMBOL(printk_ratelimit);
+EXPORT_SYMBOL(__printk_ratelimit);
 
 /**
  * printk_timed_ratelimit - caller-controlled printk ratelimiting
@@ -1336,4 +1477,123 @@ bool printk_timed_ratelimit(unsigned long *caller_jiffies,
         return false;
 }
 EXPORT_SYMBOL(printk_timed_ratelimit);
+
+static DEFINE_SPINLOCK(dump_list_lock);
+static LIST_HEAD(dump_list);
+
+/**
+ * kmsg_dump_register - register a kernel log dumper.
+ * @dumper: pointer to the kmsg_dumper structure
+ *
+ * Adds a kernel log dumper to the system. The dump callback in the
+ * structure will be called when the kernel oopses or panics and must be
+ * set. Returns zero on success and %-EINVAL or %-EBUSY otherwise.
+ */
+int kmsg_dump_register(struct kmsg_dumper *dumper)
+{
+        unsigned long flags;
+        int err = -EBUSY;
+
+        /* The dump callback needs to be set */
+        if (!dumper->dump)
+                return -EINVAL;
+
+        spin_lock_irqsave(&dump_list_lock, flags);
+        /* Don't allow registering multiple times */
+        if (!dumper->registered) {
+                dumper->registered = 1;
+                list_add_tail(&dumper->list, &dump_list);
+                err = 0;
+        }
+        spin_unlock_irqrestore(&dump_list_lock, flags);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_register);
+
+/**
+ * kmsg_dump_unregister - unregister a kmsg dumper.
+ * @dumper: pointer to the kmsg_dumper structure
+ *
+ * Removes a dump device from the system. Returns zero on success and
+ * %-EINVAL otherwise.
+ */
+int kmsg_dump_unregister(struct kmsg_dumper *dumper)
+{
+        unsigned long flags;
+        int err = -EINVAL;
+
+        spin_lock_irqsave(&dump_list_lock, flags);
+        if (dumper->registered) {
+                dumper->registered = 0;
+                list_del(&dumper->list);
+                err = 0;
+        }
+        spin_unlock_irqrestore(&dump_list_lock, flags);
+
+        return err;
+}
+EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
+
+static const char * const kmsg_reasons[] = {
+        [KMSG_DUMP_OOPS]        = "oops",
+        [KMSG_DUMP_PANIC]       = "panic",
+        [KMSG_DUMP_KEXEC]       = "kexec",
+};
+
+static const char *kmsg_to_str(enum kmsg_dump_reason reason)
+{
+        if (reason >= ARRAY_SIZE(kmsg_reasons) || reason < 0)
+                return "unknown";
+
+        return kmsg_reasons[reason];
+}
+
+/**
+ * kmsg_dump - dump kernel log to kernel message dumpers.
+ * @reason: the reason (oops, panic etc) for dumping
+ *
+ * Iterate through each of the dump devices and call the oops/panic
+ * callbacks with the log buffer.
+ */
+void kmsg_dump(enum kmsg_dump_reason reason)
+{
+        unsigned long end;
+        unsigned chars;
+        struct kmsg_dumper *dumper;
+        const char *s1, *s2;
+        unsigned long l1, l2;
+        unsigned long flags;
+
+        /* Theoretically, the log could move on after we do this, but
+           there's not a lot we can do about that. The new messages
+           will overwrite the start of what we dump. */
+        spin_lock_irqsave(&logbuf_lock, flags);
+        end = log_end & LOG_BUF_MASK;
+        chars = logged_chars;
+        spin_unlock_irqrestore(&logbuf_lock, flags);
+
+        if (chars > end) {
+                s1 = log_buf + log_buf_len - chars + end;
+                l1 = chars - end;
+
+                s2 = log_buf;
+                l2 = end;
+        } else {
+                s1 = "";
+                l1 = 0;
+
+                s2 = log_buf + end - chars;
+                l2 = chars;
+        }
+
+        if (!spin_trylock_irqsave(&dump_list_lock, flags)) {
+                printk(KERN_ERR "dump_kmsg: dump list lock is held during %s, skipping dump\n",
+                                kmsg_to_str(reason));
+                return;
+        }
+        list_for_each_entry(dumper, &dump_list, list)
+                dumper->dump(dumper, reason, s1, l1, s2, l2);
+        spin_unlock_irqrestore(&dump_list_lock, flags);
+}
 #endif