printk: add interfaces for external access to the log buffer

Add two new functions for reading the kernel log buffer.  The intention is for
them to be used by recovery/dump/debug code so the kernel log can be easily
retrieved/parsed in a crash scenario, but they are generic enough for other
people to dream up other fun uses.

[akpm@linux-foundation.org: buncha fixes]
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Cc: Robin Getz <rgetz@blackfin.uclinux.org>
Cc: Greg Ungerer <gerg@snapgear.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Cc: Paul Mundt <lethal@linux-sh.org>
Acked-by: Tim Bird <tim.bird@am.sony.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 5fdbc814c2eb73ad5330be18348cee1a629210f9..c680e1e6e9a3cb2513f6e3e94dd6957d4c5f9cad 100644 (file)
--- 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 b2b5c3a22a36b302da177fafae653740f7eeeddf..52493474f0abafdfd7939ab57f3f2d6ad2006695 100644 (file)
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -219,6 +219,58 @@ 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:
  *