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Commit fe3d8ad3 authored by Feng Tang's avatar Feng Tang Committed by Linus Torvalds
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console: prevent registered consoles from dumping old kernel message over again 



For a platform with many consoles like:
 "console=tty1 console=ttyMFD2 console=ttyS0 earlyprintk=mrst"

Each time when the non "selected_console" (tty1 and ttyMFD2 here) get
registered, the existing kernel message will be printed out on registered
consoles again, the "mrst" early console will get some same message for 3
times, and "tty1" will get some for twice.

As suggested by Andrew Morton, every time a new console is registered, it
will be set as the "exclusive" console which will dump the already
existing kernel messages.

Signed-off-by: default avatarFeng Tang <feng.tang@intel.com>
Cc: Greg KH <gregkh@suse.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7bf69395

kernel/printk.c

+18 −0
Original line number Diff line number Diff line
@@ -112,6 +112,11 @@ static unsigned log_start; /* Index into log_buf: next char to be read by syslog 
static unsigned con_start;	/* Index into log_buf: next char to be sent to consoles */

static unsigned log_end;	/* Index into log_buf: most-recently-written-char + 1 */



/*

 * If exclusive_console is non-NULL then only this console is to be printed to.

 */

static struct console *exclusive_console;



/*

 *	Array of consoles built from command line options (console=)

 */
@@ -476,6 +481,8 @@ static void __call_console_drivers(unsigned start, unsigned end) 
	struct console *con;



	for_each_console(con) {

		if (exclusive_console && con != exclusive_console)

			continue;

		if ((con->flags & CON_ENABLED) && con->write &&

				(cpu_online(smp_processor_id()) ||

				(con->flags & CON_ANYTIME)))
@@ -1230,6 +1237,11 @@ void console_unlock(void) 
		local_irq_restore(flags);

	}

	console_locked = 0;



	/* Release the exclusive_console once it is used */

	if (unlikely(exclusive_console))

		exclusive_console = NULL;



	up(&console_sem);

	spin_unlock_irqrestore(&logbuf_lock, flags);

	if (wake_klogd)
@@ -1464,6 +1476,12 @@ void register_console(struct console *newcon) 
		spin_lock_irqsave(&logbuf_lock, flags);

		con_start = log_start;

		spin_unlock_irqrestore(&logbuf_lock, flags);

		/*

		 * We're about to replay the log buffer.  Only do this to the

		 * just-registered console to avoid excessive message spam to

		 * the already-registered consoles.

		 */

		exclusive_console = newcon;

	}

	console_unlock();

	console_sysfs_notify();