[patch] Fixes and cleanups for earlyprintk aka boot console.

[Gerd Hoffmann <kraxel@suse.de>]

  Hi,

The console subsystem already has an idea of a boot console, using the
CON_BOOT flag.  The implementation has some flaws though.  The major
problem is that presence of a boot console makes register_console()
ignore any other console devices (unless explicitly specified on the
kernel command line).

This patch fixes the console selection code to *not* consider a boot
console a full-featured one, so the first non-boot console registering
will become the default console instead.  This way the unregister call
for the boot console in the register_console() function actually
triggers and the handover from the boot console to the real console
device works smoothly.  Added a printk for the handover, so you know
which console device the output goes to when the boot console stops
printing messages.

The disable_early_printk() call is obsolete with that patch, explicitly
disabling the early console isn't needed any more as it works
automagically with that patch.

I've walked through the tree, dropped all disable_early_printk()
instances found below arch/ and tagged the consoles with CON_BOOT if
needed.

The code is tested on x86 only so far.  It is probably a good idea to
run it in -mm for a while to shake out any architecture issues which
might show up.  Comments?

cheers,

  Gerd

-- 
Gerd Hoffmann <kraxel@suse.de>

Fixes and cleanups for earlyprintk aka boot console.

The console subsystem already has an idea of a boot console, using the
CON_BOOT flag.  The implementation has some flaws though.  The major
problem is that presence of a boot console makes register_console()
ignore any other console devices (unless explicitly specified on the
kernel command line).

This patch fixes the console selection code to *not* consider a boot
console a full-featured one, so the first non-boot console registering
will become the default console instead.  This way the unregister call
for the boot console in the register_console() function actually
triggers and the handover from the boot console to the real console
device works smoothly.  Added a printk for the handover, so you know
which console device the output goes to when the boot console stops
printing messages.

The disable_early_printk() call is obsolete with that patch, explicitly
disabling the early console isn't needed any more as it works
automagically with that patch.

I've walked through the tree, dropped all disable_early_printk()
instances found below arch/ and tagged the consoles with CON_BOOT if
needed.  The code is tested on x86 only so far.

Signed-off-by: Gerd Hoffmann <kraxel@suse.de>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
---
 arch/alpha/kernel/setup.c         |    9 ---------
 arch/alpha/kernel/srmcons.c       |    2 +-
 arch/mips/cobalt/console.c        |    5 -----
 arch/mips/dec/prom/console.c      |    5 +----
 arch/mips/sgi-ip27/ip27-console.c |    5 -----
 arch/powerpc/kernel/udbg.c        |   14 +-------------
 arch/sh/kernel/early_printk.c     |   18 ++++++------------
 arch/sh64/kernel/early_printk.c   |    8 +-------
 arch/x86_64/kernel/early_printk.c |   20 +++++---------------
 drivers/char/tty_io.c             |    5 -----
 kernel/printk.c                   |   26 ++++++++++++++++----------
 11 files changed, 31 insertions(+), 86 deletions(-)

===================================================================
Index: paravirt-2.6.20-git14-hg791/arch/x86_64/kernel/early_printk.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/x86_64/kernel/early_printk.c
+++ paravirt-2.6.20-git14-hg791/arch/x86_64/kernel/early_printk.c
@@ -244,22 +244,12 @@ static int __init setup_early_printk(cha
  		early_console = &simnow_console;
  		keep_early = 1;
 	}
+
+	if (keep_early)
+		early_console->flags &= ~CON_BOOT;
+	else
+		early_console->flags |= CON_BOOT;
 	register_console(early_console);
 	return 0;
 }
-
 early_param("earlyprintk", setup_early_printk);
-
-void __init disable_early_printk(void)
-{
-	if (!early_console_initialized || !early_console)
-		return;
-	if (!keep_early) {
-		printk("disabling early console\n");
-		unregister_console(early_console);
-		early_console_initialized = 0;
-	} else {
-		printk("keeping early console\n");
-	}
-}
-
Index: paravirt-2.6.20-git14-hg791/kernel/printk.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/kernel/printk.c
+++ paravirt-2.6.20-git14-hg791/kernel/printk.c
@@ -931,8 +931,16 @@ void register_console(struct console *co
 {
 	int i;
 	unsigned long flags;
+	struct console *bootconsole = NULL;
 
-	if (preferred_console < 0)
+	if (console_drivers) {
+		if (console->flags & CON_BOOT)
+			return;
+		if (console_drivers->flags & CON_BOOT)
+			bootconsole = console_drivers;
+	}
+
+	if (preferred_console < 0 || bootconsole || !console_drivers)
 		preferred_console = selected_console;
 
 	/*
@@ -978,8 +986,11 @@ void register_console(struct console *co
 	if (!(console->flags & CON_ENABLED))
 		return;
 
-	if (console_drivers && (console_drivers->flags & CON_BOOT)) {
-		unregister_console(console_drivers);
+	if (bootconsole) {
+		printk(KERN_INFO "console handover: boot [%s%d] -> real [%s%d]\n",
+		       bootconsole->name, bootconsole->index,
+		       console->name, console->index);
+		unregister_console(bootconsole);
 		console->flags &= ~CON_PRINTBUFFER;
 	}
 
@@ -1030,16 +1041,11 @@ int unregister_console(struct console *c
 		}
 	}
 
-	/* If last console is removed, we re-enable picking the first
-	 * one that gets registered. Without that, pmac early boot console
-	 * would prevent fbcon from taking over.
-	 *
+	/*
 	 * If this isn't the last console and it has CON_CONSDEV set, we
 	 * need to set it on the next preferred console.
 	 */
-	if (console_drivers == NULL)
-		preferred_console = selected_console;
-	else if (console->flags & CON_CONSDEV)
+	if (console_drivers != NULL && console->flags & CON_CONSDEV)
 		console_drivers->flags |= CON_CONSDEV;
 
 	release_console_sem();
Index: paravirt-2.6.20-git14-hg791/drivers/char/tty_io.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/drivers/char/tty_io.c
+++ paravirt-2.6.20-git14-hg791/drivers/char/tty_io.c
@@ -141,8 +141,6 @@ static DECLARE_MUTEX(allocated_ptys_lock
 static int ptmx_open(struct inode *, struct file *);
 #endif
 
-extern void disable_early_printk(void);
-
 static void initialize_tty_struct(struct tty_struct *tty);
 
 static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
@@ -3880,9 +3878,6 @@ void __init console_init(void)
 	 * set up the console device so that later boot sequences can 
 	 * inform about problems etc..
 	 */
-#ifdef CONFIG_EARLY_PRINTK
-	disable_early_printk();
-#endif
 	call = __con_initcall_start;
 	while (call < __con_initcall_end) {
 		(*call)();
Index: paravirt-2.6.20-git14-hg791/arch/alpha/kernel/setup.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/alpha/kernel/setup.c
+++ paravirt-2.6.20-git14-hg791/arch/alpha/kernel/setup.c
@@ -744,15 +744,6 @@ setup_arch(char **cmdline_p)
 	paging_init();
 }
 
-void __init
-disable_early_printk(void)
-{
-	if (alpha_using_srm && srmcons_output) {
-		unregister_srm_console();
-		srmcons_output = 0;
-	}
-}
-
 static char sys_unknown[] = "Unknown";
 static char systype_names[][16] = {
 	"0",
Index: paravirt-2.6.20-git14-hg791/arch/alpha/kernel/srmcons.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/alpha/kernel/srmcons.c
+++ paravirt-2.6.20-git14-hg791/arch/alpha/kernel/srmcons.c
@@ -300,7 +300,7 @@ static struct console srmcons = {
 	.write		= srm_console_write,
 	.device		= srm_console_device,
 	.setup		= srm_console_setup,
-	.flags		= CON_PRINTBUFFER,
+	.flags		= CON_PRINTBUFFER | CON_BOOT,
 	.index		= -1,
 };
 
Index: paravirt-2.6.20-git14-hg791/arch/mips/cobalt/console.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/mips/cobalt/console.c
+++ paravirt-2.6.20-git14-hg791/arch/mips/cobalt/console.c
@@ -40,8 +40,3 @@ void __init cobalt_early_console(void)
 
 	printk("Cobalt: early console registered\n");
 }
-
-void __init disable_early_printk(void)
-{
-	unregister_console(&cons_info);
-}
Index: paravirt-2.6.20-git14-hg791/arch/mips/dec/prom/console.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/mips/dec/prom/console.c
+++ paravirt-2.6.20-git14-hg791/arch/mips/dec/prom/console.c
@@ -29,7 +29,7 @@ static void __init prom_console_write(st
 static struct console promcons __initdata = {
 	.name	= "prom",
 	.write	= prom_console_write,
-	.flags	= CON_PRINTBUFFER,
+	.flags	= CON_PRINTBUFFER | CON_BOOT,
 	.index	= -1,
 };
 
@@ -50,6 +50,3 @@ void __init unregister_prom_console(void
 		promcons_output = 0;
 	}
 }
-
-void disable_early_printk(void)
-	__attribute__((alias("unregister_prom_console")));
Index: paravirt-2.6.20-git14-hg791/arch/mips/sgi-ip27/ip27-console.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/mips/sgi-ip27/ip27-console.c
+++ paravirt-2.6.20-git14-hg791/arch/mips/sgi-ip27/ip27-console.c
@@ -67,8 +67,3 @@ __init void ip27_setup_console(void)
 {
 	register_console(&ioc3_console);
 }
-
-void __init disable_early_printk(void)
-{
-	unregister_console(&ioc3_console);
-}
Index: paravirt-2.6.20-git14-hg791/arch/powerpc/kernel/udbg.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/powerpc/kernel/udbg.c
+++ paravirt-2.6.20-git14-hg791/arch/powerpc/kernel/udbg.c
@@ -142,24 +142,12 @@ static void udbg_console_write(struct co
 static struct console udbg_console = {
 	.name	= "udbg",
 	.write	= udbg_console_write,
-	.flags	= CON_PRINTBUFFER | CON_ENABLED,
+	.flags	= CON_PRINTBUFFER | CON_ENABLED | CON_BOOT,
 	.index	= -1,
 };
 
 static int early_console_initialized;
 
-void __init disable_early_printk(void)
-{
-	if (!early_console_initialized)
-		return;
-	if (strstr(boot_command_line, "udbg-immortal")) {
-		printk(KERN_INFO "early console immortal !\n");
-		return;
-	}
-	unregister_console(&udbg_console);
-	early_console_initialized = 0;
-}
-
 /* called by setup_system */
 void register_early_udbg_console(void)
 {
Index: paravirt-2.6.20-git14-hg791/arch/sh/kernel/early_printk.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/sh/kernel/early_printk.c
+++ paravirt-2.6.20-git14-hg791/arch/sh/kernel/early_printk.c
@@ -192,20 +192,14 @@ int __init setup_early_printk(char *buf)
 	}
 #endif
 
-	if (likely(early_console))
+	if (likely(early_console)) {
+		if (keep_early)
+			early_console->flags &= ~CON_BOOT;
+		else
+			early_console->flags |= CON_BOOT;
 		register_console(early_console);
+	}
 
 	return 0;
 }
 early_param("earlyprintk", setup_early_printk);
-
-void __init disable_early_printk(void)
-{
-	if (!early_console_initialized || !early_console)
-		return;
-	if (!keep_early) {
-		printk("disabling early console\n");
-		unregister_console(early_console);
-	} else
-		printk("keeping early console\n");
-}
Index: paravirt-2.6.20-git14-hg791/arch/sh64/kernel/early_printk.c
===================================================================
--- paravirt-2.6.20-git14-hg791.orig/arch/sh64/kernel/early_printk.c
+++ paravirt-2.6.20-git14-hg791/arch/sh64/kernel/early_printk.c
@@ -79,7 +79,7 @@ static struct console sh_console = {
 	.name		= "scifcon",
 	.write		= sh_console_write,
 	.setup		= sh_console_setup,
-	.flags		= CON_PRINTBUFFER,
+	.flags		= CON_PRINTBUFFER | CON_BOOT,
 	.index		= -1,
 };
 
@@ -97,9 +97,3 @@ void __init enable_early_printk(void)
 
 	register_console(&sh_console);
 }
-
-void disable_early_printk(void)
-{
-	unregister_console(&sh_console);
-}
-