When Linux kernel panic, what can we do ?

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本文介绍如何在Freescale iMX515硬件上，使用Linux内核2.6.31，在LCD显示“boot failed!”信息，以响应内核panic情况。通过修改fbcon.c和panic.c文件实现。

Hardware： Freescale iMX515
Software： Linux kernel 2.6.31
Target requirement: show "boot failed !" in LCD while Linux kernel panic.
Technology methods： use Notifier chains of kernel to do.
Reference to：
[1]. http://bbs.chinaunix.net/thread-2011776-1-1.html
[2]. Linux kernel source code tree: /include/linux/notifier.h, kernel/notifier.c
Modification souce code:
drivers/video/console/fbcon.c
kernel/panic.c

1. modify drivers/video/console/fbcon.c

1.1 modify function fbcon_init()

static void fbcon_init(struct vc_data *vc, int init)
{
	/* omit ... */

	/* show boot information in LCD */
	#if defined(CONFIG_LOGO_LINUX_CLUT224)
	show_boot.info = registered_fb[con2fb_map[vc->vc_num]];
	show_boot.ops = show_boot.info->fbcon_par;
	show_boot.vc = vc;
	show_boot.p = &fb_display[vc->vc_num];
	ret = kernel_thread(show_boot_info_thread, (void *) &show_boot, CLONE_KERNEL);
	if(ret < 0)
	{
		pr_err("Failed to start show_boot_info_thread daemon\n");
	}
	else
	{
		pr_notice("Successful to start show_boot_info_thread daemon\n");
	}	
	#endif /* CONFIG_LOGO_LINUX_CLUT224 */
}

1.2 add below codes in this file

#if defined(CONFIG_LOGO_LINUX_CLUT224)
/* Wenxy add begin, 20111014 */
struct show_boot_in_lcd
{
	struct fbcon_ops *ops;
	struct vc_data *vc;
	struct fb_info *info;
	struct display *p;	
};

static struct show_boot_in_lcd show_boot; 

static RAW_NOTIFIER_HEAD(lcd_show_chain); 	/* show error information in LCD */

/* LCD show error information */
static int lcd_tip_error(struct notifier_block *this, unsigned long event, void *ptr)
{
	struct vc_data *vc;
	struct fb_info *info;
	struct fbcon_ops *ops;
	struct display *p;
	int yy; 
	int xx;
	int fg;
	int bg;
	unsigned int len;
	unsigned char tips[]="b o o t   f a i l e d   ! ";
	
	if(!show_boot.ops)
	{
		return -EINVAL;
	}
	
	vc = show_boot.vc;
	info = show_boot.info;
	ops = show_boot.ops;
	p = show_boot.p;	

	xx = 5; 	/* 62 */
	yy = 28;
	fg = 0x04; 	/* red: 0x04 */
	bg = 0x7; 	/* vc->vc_halfcolor; */
	len = strlen(tips)/2;
	ops->putcs(vc, info, (unsigned short *)tips, len, real_y(p, yy), real_y(p, xx), fg, bg);
	
	return 0; 
}


static struct notifier_block lcd_notifier_error =
{        
	.notifier_call = lcd_tip_error,
};


int lcd_notifier_call_chain(unsigned long val, void *v)
{
	return raw_notifier_call_chain(&lcd_show_chain, 1, NULL);

}
EXPORT_SYMBOL(lcd_notifier_call_chain);


/* Show boot information in LCD */
static int show_boot_info_thread(void * dummy)
{
	struct vc_data *vc;
	struct fb_info *info;
	struct fbcon_ops *ops;
	struct display *p;	
	const unsigned short *s;
	int count; 
	int yy; 
	int xx;
	int fg;
	int bg;
	int softback_lines;
	int mode;
	unsigned int n, index, len1, len2;
	#define FM_VERSION "Firmware version: " 	/* UTS_RELEASE */
	unsigned char version[256], substr1[128], substr2[128];
	unsigned char bar[]="                                                                                                                                                                       ";

	unsigned int time_count, pass_count, bar_count;
	#define SLEEP_MS			100	/* millisecond, 100,500 */
	#define BOOT_KERNEL_TIME	10	/* second, 10 */
	#define BAR_LEN				90	/* boot progress bar length */
	
	if(!dummy)
	{
		return -EINVAL;
	}
	vc = ((struct show_boot_in_lcd *)dummy)->vc;
	info = ((struct show_boot_in_lcd *)dummy)->info;
	ops = ((struct show_boot_in_lcd *)dummy)->ops;
	p = ((struct show_boot_in_lcd *)dummy)->p;

	time_count = (BOOT_KERNEL_TIME*1000)/SLEEP_MS;
	pass_count = 1;
	/*
	time_count = 180;
	pass_count = 1;
	bar_count = BAR_LEN/time_count;
	*/

	/* register notifier block */
	if(raw_notifier_chain_register(&lcd_show_chain, &lcd_notifier_error))
	{
		pr_warning("Warning: into %s, %s, raw_notifier_chain_register call failed\n", __FILE__, __FUNCTION__);
	}
	
	/* show version in LCD */
	memset(substr1, 0, sizeof(substr1));
	memset(substr2, 0, sizeof(substr2));
	memset(version, 0, sizeof(version));
	memcpy(substr1, FM_VERSION, sizeof(FM_VERSION));
	memcpy(substr2, UTS_RELEASE, sizeof(UTS_RELEASE));
	
	len1 = 2*strlen(FM_VERSION);
	index = 0;
	for(n = 0; n < len1; n+=2)
	{
		version[n] = substr1[index++];
		version[n+1] = ' ';
	}
	
	len2 = 2*strlen(UTS_RELEASE);
	index = 0;
	for(n = 0; n < len2; n+=2)
	{
		version[len1 + n] = substr2[index++];
		version[len1 + n+1] = ' ';
	}	
	/*pr_notice("Debug:%s\n", version);*/
	
	xx = 55; 	/* 62 */
	yy = 28;
	fg = 0x00; 	/* 0x00 */
	bg = 0x7; 	/* vc->vc_halfcolor; */
	ops->putcs(vc, info, (unsigned short *)version, (len1+len2)/2, real_y(p, yy), real_y(p, xx), fg, bg);
	
	/* draw progress bar in LCD */
	xx = 5;
	yy = 26;
	fg = 0x7;
	bg = fg;
	ops->putcs(vc, info, (unsigned short *)bar, BAR_LEN, real_y(p, yy), real_y(p, xx), fg, bg);
		
	while(pass_count <= time_count)
	{
		xx = 5;
		yy = 26;
		fg = 0x2;
		bg = 0x2;	
		
		ops->putcs(vc, info, (unsigned short *)bar, pass_count>BAR_LEN?BAR_LEN:pass_count, \
			real_y(p, yy), real_y(p, xx), fg, bg);
		/*
		ops->putcs(vc, info, (unsigned short *)bar, pass_count*bar_count, \
			real_y(p, yy), real_y(p, xx), fg, bg);
		*/
		pass_count++;
		
		#if 0
		ops->cursor_flash = 0; /* stop cursor flash */
		vc->vc_x = 0; 		/* Cursor position */
		vc->vc_y = 0;
		vc->vc_deccm = 0;	/* Cursor cannot Visible */
		#endif	
		
		mdelay(SLEEP_MS);
	}

	pr_notice("Successful to exit show_boot_info_thread daemon\n");
	#if 0
	vc->vc_deccm = 1;
	ops->cursor_flash = 1;
	#endif
	/* unregister notifier block */
	if(raw_notifier_chain_unregister(&lcd_show_chain, &lcd_notifier_error))
	{
		pr_warning("Warning: into %s, %s, raw_notifier_chain_unregister call failed\n", __FILE__, __FUNCTION__);
	}
	
	return 0;
}
/* Wenxy add end */
#endif /* LOGO_LINUX_CLUT224 */

2. modify kernel/panic.c
2.1 add the code in this file

extern int lcd_notifier_call_chain(unsigned long val, void *v);

2.2 modify function panic()

/**
 *	panic - halt the system
 *	@fmt: The text string to print
 *
 *	Display a message, then perform cleanups.
 *
 *	This function never returns.
 */
NORET_TYPE void panic(const char * fmt, ...)
{
	static char buf[1024];
	va_list args;
	long i;
	
	#if defined(CONFIG_LOGO_LINUX_CLUT224)
	/* notification show error information in LCD */
	if(lcd_notifier_call_chain(1, NULL))
	{
		pr_warning("Warning: into %s, %s, lcd_notifier_call_chain call failed\n", __FILE__, __FUNCTION__);
	}
	/*mdelay(1 * 1000);*/
	#endif /* LOGO_LINUX_CLUT224 */
	
	/*
	 * It's possible to come here directly from a panic-assertion and
	 * not have preempt disabled. Some functions called from here want
	 * preempt to be disabled. No point enabling it later though...
	 */
	preempt_disable();

	bust_spinlocks(1);
	va_start(args, fmt);
	vsnprintf(buf, sizeof(buf), fmt, args);
	va_end(args);
	printk(KERN_EMERG "Kernel panic - not syncing: %s\n",buf);
#ifdef CONFIG_DEBUG_BUGVERBOSE
	dump_stack();
#endif

	/* omit ... */
}

3. conifg Kernel
#make menuconfig
Select this menu items
Device Drivers ---> Graphics support ---> [*] Bootup logo ---> [*] Standard 224-color Linux logo (NEW)

4. build Kernel
#make -j 4; make uImage