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 5fdbc81..c680e1e 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -172,6 +172,9 @@
__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 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 b2b5c3a..5249347 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -220,6 +220,58 @@
#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.
