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Commit 0b15d04a authored by Mike Frysinger's avatar Mike Frysinger Committed by Linus Torvalds
Browse files

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: default avatarMike 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: default avatarTim Bird <tim.bird@am.sony.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent d823e3e7

include/linux/kernel.h

+6 −0
Original line number Diff line number Diff line
@@ -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);

kernel/printk.c

+52 −0
Original line number Diff line number Diff line
@@ -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:

 *