VT driver/char/console.c, kernel 2.4.22

Hello,

Abstract:
-----------

This patch makes effective the ability to redirect kernel messages to a specific VT through the 'console=' argument. It is already supposed to work (that is, kernel messages only appear on /dev/tty1 or /dev/tty2 or ...) but actually does not (messages are always sent to the foreground console, that is /dev/tty or /dev/tty0).

Sebastian Schmidt <yath -at- yath.eu.org> already noticed the problem in March 2003. Benjamin Reed <breed -at- almaden.ibm.com> wrote a patch two years ago to correct this. Here is a link to his post: http://www.ussg.iu.edu/hypermail/linux/kernel/0108.2/1455.html
It seems have never been taken in account.

The patch I made is almost based on Benjamin's patch, completing its effectiveness via vt_console_setup().

Relative comment:
---------------------

In relation to this patch, I want to say that many many websites, FAQs, ... say that you must have something like console="/dev/ttyX CONSOLE=/dev/ttyN" to redirect the kernel and init messages.

About 'CONSOLE=', that's true because this is a environment variable that /sbin/init obtains. About 'console=', it's completly wrong ! 'console=' expects a driver name (example: "tty", "tty1", "ttyS0"), not device file name. Only the Linux source code reading and a few websites says the right usage of 'console='.

Question
-----------
Is the way I attached the patch "correct" ? Must I Cc: it to Marcello or someone else ? I didn't find the ideal maintainer in linux/MAINTAINERS.

Bye.

Baptiste Malguy - http://baptiste.malguy.net
Ingénieur en informatique libre

*** linux-2.4.22/drivers/char/console.c 2002-11-29 00:53:12.000000000 +0100
--- work/linux-2.4.22-bm1/drivers/char/console.c 2003-11-28 16:45:58.000000000 +0100
***************
*** 144,149 ****
--- 144,150 ----
static int con_open(struct tty_struct *, struct file *); static void vc_init(unsigned int console, unsigned int rows,
unsigned int cols, int do_clear);
+ static void con_setup_vt(unsigned int currcons);
static void blank_screen(unsigned long dummy);
static void gotoxy(int currcons, int new_x, int new_y); static void save_cur(int currcons);
***************
*** 2178,2187 ****
--- 2179,2203 ----
return MKDEV(TTY_MAJOR, c->index ? c->index : fg_console + 1);
}

+ int vt_console_setup(struct console *co, char *options)
+ {
+ if (co == NULL)
+ return -1;
+
+ if (co->index > 0 &&
+ co->index < MAX_NR_CONSOLES) {
+ con_setup_vt(co->index - 1);
+ kmsg_redirect = co->index;
+ }
+
+ return 0;
+ }
+
struct console vt_console_driver = {
name: "tty",
write: vt_console_print,
device: vt_console_device,
+ setup: vt_console_setup,
unblank: unblank_screen,
flags: CON_PRINTBUFFER,
index: -1,
***************
*** 2432,2437 ****
--- 2448,2471 ----
}

/*
+ * Setup a new VT
+ */
+ static void __init con_setup_vt(unsigned int currcons)
+ {
+ if (vc_cons[currcons].d) return;
+
+ vc_cons[currcons].d = (struct vc_data *)
+ alloc_bootmem(sizeof(struct vc_data));
+ vt_cons[currcons] = (struct vt_struct *)
+ alloc_bootmem(sizeof(struct vt_struct));
+ visual_init(currcons, 1);
+ screenbuf = (unsigned short *) alloc_bootmem(screenbuf_size);
+ kmalloced = 0;
+ vc_init(currcons, video_num_lines, video_num_columns,
+ currcons || !sw->con_save_screen);
+ }
+
+ /*
* This routine initializes console interrupts, and does nothing
* else. If you want the screen to clear, call tty_write with
* the appropriate escape-sequence.
***************
*** 2498,2512 ****
* kmalloc is not running yet - we use the bootmem allocator. */
for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
! vc_cons[currcons].d = (struct vc_data *)
! alloc_bootmem(sizeof(struct vc_data));
! vt_cons[currcons] = (struct vt_struct *)
! alloc_bootmem(sizeof(struct vt_struct));
! visual_init(currcons, 1);
! screenbuf = (unsigned short *) alloc_bootmem(screenbuf_size);
! kmalloced = 0;
! vc_init(currcons, video_num_lines, video_num_columns,
! currcons || !sw->con_save_screen);
}
currcons = fg_console = 0;
master_display_fg = vc_cons[currcons].d;
--- 2532,2538 ----
* kmalloc is not running yet - we use the bootmem allocator. */
for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
! con_setup_vt(currcons);
}
currcons = fg_console = 0;
master_display_fg = vc_cons[currcons].d;

If there really are FAQ reporting this, it might be simpler to make the kernel accept /dev/XXX than to try to fix all FAQs, and it would be more intuitive to people who type on lilo command line.

You'd better send an "unified diff" (diff -u) which includes one level of kernel directory. You diff then starts like this :
--- linux-2.4.22/drivers/char/console
+++ linux-2.4.22-bm1/drivers/char/console

And all close changes are merged in a chunk with lines starting with + and -. Then it's more convenient to compare small changes.

Please take a look at Documentation/SubmittingPatches for more info.

It's good to Cc Marcelo when you're sure it's an obvious patch that must be applied, but if you think it may be discussed here, it's better not to flood his mailbox, considering many people reply to all recipients.

Cheers,
Willy

I guess you are right. However, all I've done (and again, essentially, using someone else code) is to fix of bug. Changing the way the 'console=' argument works is more a design stuff.

If all the console drivers' names are based on the device file name (that is "tty" for "/dev/tty1", ort "/dev/tty2", ...) it can be easily done by dropping "/dev/" from the 'console=' argument value, in one C file. However, a device file name can be anything you want. So the "/dev/" wouldn't work.

I don't know if that's the good way to do it. Maybe a more complete work, like looking at the device file, its major and minor and the corresponding driver, would be a better idea.

Baptiste Malguy - http://baptiste.malguy.net
Ingénieur en informatique libre

@@ -144,6 +144,7 @@
 static int con_open(struct tty_struct *, struct file *);
 static void vc_init(unsigned int console, unsigned int rows,
 		    unsigned int cols, int do_clear);
+static void con_setup_vt(unsigned int currcons);
 static void blank_screen(unsigned long dummy);
 static void gotoxy(int currcons, int new_x, int new_y);
 static void save_cur(int currcons);

@@ -2178,10 +2179,25 @@
 	return MKDEV(TTY_MAJOR, c->index ? c->index : fg_console + 1);
 }
 
+int vt_console_setup(struct console *co, char *options)
+{
+	if (co == NULL)
+		return -1;
+	
+	if (co->index > 0 &&
+	    co->index < MAX_NR_CONSOLES) {
+		con_setup_vt(co->index - 1);
+		kmsg_redirect = co->index;
+	}
+
+	return 0;
+}
+
 struct console vt_console_driver = {
 	name:		"tty",
 	write:		vt_console_print,
 	device:		vt_console_device,
+	setup:		vt_console_setup,
 	unblank:	unblank_screen,
 	flags:		CON_PRINTBUFFER,
 	index:		-1,

@@ -2432,6 +2448,24 @@
 }
 
 /*
+ * Setup a new VT
+ */
+static void __init con_setup_vt(unsigned int currcons)
+{
+	if (vc_cons[currcons].d) return;
+	
+	vc_cons[currcons].d = (struct vc_data *)
+		alloc_bootmem(sizeof(struct vc_data));
+	vt_cons[currcons] = (struct vt_struct *)
+		alloc_bootmem(sizeof(struct vt_struct));
+	visual_init(currcons, 1);
+	screenbuf = (unsigned short *) alloc_bootmem(screenbuf_size);
+	kmalloced = 0;
+	vc_init(currcons, video_num_lines, video_num_columns, 
+		currcons || !sw->con_save_screen);
+}
+
+/*
  * This routine initializes console interrupts, and does nothing
  * else. If you want the screen to clear, call tty_write with
  * the appropriate escape-sequence.

@@ -2498,15 +2532,7 @@
 	 * kmalloc is not running yet - we use the bootmem allocator.
 	 */
 	for (currcons = 0; currcons < MIN_NR_CONSOLES; currcons++) {
-		vc_cons[currcons].d = (struct vc_data *)
-				alloc_bootmem(sizeof(struct vc_data));
-		vt_cons[currcons] = (struct vt_struct *)
-				alloc_bootmem(sizeof(struct vt_struct));
-		visual_init(currcons, 1);
-		screenbuf = (unsigned short *) alloc_bootmem(screenbuf_size);
-		kmalloced = 0;
-		vc_init(currcons, video_num_lines, video_num_columns, 
-			currcons || !sw->con_save_screen);
+		con_setup_vt(currcons); 
 	}
 	currcons = fg_console = 0;
 	master_display_fg = vc_cons[currcons].d;