2 files changed, 58 insertions, 0 deletions

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 5fdbc814c2eb..c680e1e6e9a3 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -172,6 +172,9 @@ asmlinkage int vprintk(const char *fmt, va_list args)
         __attribute__ ((format (printf, 1, 0)));
 asmlinkage int printk(const char * fmt, ...)
         __attribute__ ((format (printf, 1, 2))) __cold;
+extern int log_buf_get_len(void);
+extern int log_buf_read(int idx);
+extern int log_buf_copy(char *dest, int idx, int len);
 #else
 static inline int vprintk(const char *s, va_list args)
         __attribute__ ((format (printf, 1, 0)));
@@ -179,6 +182,9 @@ static inline int vprintk(const char *s, va_list args) { return 0; }
 static inline int printk(const char *s, ...)
         __attribute__ ((format (printf, 1, 2)));
 static inline int __cold printk(const char *s, ...) { return 0; }
+static inline int log_buf_get_len(void) { return 0; }
+static inline int log_buf_read(int idx) { return 0; }
+static inline int log_buf_copy(char *dest, int idx, int len) { return 0; }
 #endif
 
 unsigned long int_sqrt(unsigned long);
diff --git a/kernel/printk.c b/kernel/printk.c
index b2b5c3a22a36..52493474f0ab 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -220,6 +220,58 @@ static inline void boot_delay_msec(void)
 #endif
 
 /*
+ * Return the number of unread characters in the log buffer.
+ */
+int log_buf_get_len(void)
+{
+        return logged_chars;
+}
+
+/*
+ * Copy a range of characters from the log buffer.
+ */
+int log_buf_copy(char *dest, int idx, int len)
+{
+        int ret, max;
+        bool took_lock = false;
+
+        if (!oops_in_progress) {
+                spin_lock_irq(&logbuf_lock);
+                took_lock = true;
+        }
+
+        max = log_buf_get_len();
+        if (idx < 0 || idx >= max) {
+                ret = -1;
+        } else {
+                if (len > max)
+                        len = max;
+                ret = len;
+                idx += (log_end - max);
+                while (len-- > 0)
+                        dest[len] = LOG_BUF(idx + len);
+        }
+
+        if (took_lock)
+                spin_unlock_irq(&logbuf_lock);
+
+        return ret;
+}
+
+/*
+ * Extract a single character from the log buffer.
+ */
+int log_buf_read(int idx)
+{
+        char ret;
+
+        if (log_buf_copy(&ret, idx, 1) == 1)
+                return ret;
+        else
+                return -1;
+}
+
+/*
  * Commands to do_syslog:
  *
  *      0 -- Close the log.  Currently a NOP.