kdb_io.c

/*
 * Kernel Debugger Architecture Independent Console I/O handler
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (c) 1999-2006 Silicon Graphics, Inc.  All Rights Reserved.
 * Copyright (c) 2009 Wind River Systems, Inc.  All Rights Reserved.
 */

#include <linux/types.h>
#include <linux/ctype.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/kdev_t.h>
#include <linux/console.h>
#include <linux/string.h>
#include <linux/sched.h>
#include <linux/smp.h>
#include <linux/nmi.h>
#include <linux/delay.h>
#include <linux/kgdb.h>
#include <linux/kdb.h>
#include <linux/kallsyms.h>
#include "kdb_private.h"

#define CMD_BUFLEN 256
char kdb_prompt_str[CMD_BUFLEN];

int kdb_trap_printk;
int kdb_printf_cpu = -1;

static int kgdb_transition_check(char *buffer)
{
	if (buffer[0] != '+' && buffer[0] != '$') {
		KDB_STATE_SET(KGDB_TRANS);
		kdb_printf("%s", buffer);
	} else {
		int slen = strlen(buffer);
		if (slen > 3 && buffer[slen - 3] == '#') {
			kdb_gdb_state_pass(buffer);
			strcpy(buffer, "kgdb");
			KDB_STATE_SET(DOING_KGDB);
			return 1;
		}
	}
	return 0;
}

/**
 * kdb_handle_escape() - validity check on an accumulated escape sequence.
 * @buf:	Accumulated escape characters to be examined. Note that buf
 *		is not a string, it is an array of characters and need not be
 *		nil terminated.
 * @sz:		Number of accumulated escape characters.
 *
 * Return: -1 if the escape sequence is unwanted, 0 if it is incomplete,
 * otherwise it returns a mapped key value to pass to the upper layers.
 */
static int kdb_handle_escape(char *buf, size_t sz)
{
	char *lastkey = buf + sz - 1;

	switch (sz) {
	case 1:
		if (*lastkey == '\e')
			return 0;
		break;

	case 2: /* \e<something> */
		if (*lastkey == '[')
			return 0;
		break;

	case 3:
		switch (*lastkey) {
		case 'A': /* \e[A, up arrow */
			return 16;
		case 'B': /* \e[B, down arrow */
			return 14;
		case 'C': /* \e[C, right arrow */
			return 6;
		case 'D': /* \e[D, left arrow */
			return 2;
		case '1': /* \e[<1,3,4>], may be home, del, end */
		case '3':
		case '4':
			return 0;
		}
		break;

	case 4:
		if (*lastkey == '~') {
			switch (buf[2]) {
			case '1': /* \e[1~, home */
				return 1;
			case '3': /* \e[3~, del */
				return 4;
			case '4': /* \e[4~, end */
				return 5;
			}
		}
		break;
	}

	return -1;
}

/**
 * kdb_getchar() - Read a single character from a kdb console (or consoles).
 *
 * Other than polling the various consoles that are currently enabled,
 * most of the work done in this function is dealing with escape sequences.
 *
 * An escape key could be the start of a vt100 control sequence such as \e[D
 * (left arrow) or it could be a character in its own right.  The standard
 * method for detecting the difference is to wait for 2 seconds to see if there
 * are any other characters.  kdb is complicated by the lack of a timer service
 * (interrupts are off), by multiple input sources. Escape sequence processing
 * has to be done as states in the polling loop.
 *
 * Return: The key pressed or a control code derived from an escape sequence.
 */
char kdb_getchar(void)
{
#define ESCAPE_UDELAY 1000
#define ESCAPE_DELAY (2*1000000/ESCAPE_UDELAY) /* 2 seconds worth of udelays */
	char buf[4];	/* longest vt100 escape sequence is 4 bytes */
	char *pbuf = buf;
	int escape_delay = 0;
	get_char_func *f, *f_prev = NULL;
	int key;
	static bool last_char_was_cr;

	for (f = &kdb_poll_funcs[0]; ; ++f) {
		if (*f == NULL) {
			/* Reset NMI watchdog once per poll loop */
			touch_nmi_watchdog();
			f = &kdb_poll_funcs[0];
		}

		key = (*f)();
		if (key == -1) {
			if (escape_delay) {
				udelay(ESCAPE_UDELAY);
				if (--escape_delay == 0)
					return '\e';
			}
			continue;
		}

		/*
		 * The caller expects that newlines are either CR or LF. However
		 * some terminals send _both_ CR and LF. Avoid having to handle
		 * this in the caller by stripping the LF if we saw a CR right
		 * before.
		 */
		if (last_char_was_cr && key == '\n') {
			last_char_was_cr = false;
			continue;
		}
		last_char_was_cr = (key == '\r');

		/*
		 * When the first character is received (or we get a change
		 * input source) we set ourselves up to handle an escape
		 * sequences (just in case).
		 */
		if (f_prev != f) {
			f_prev = f;
			pbuf = buf;
			escape_delay = ESCAPE_DELAY;
		}

		*pbuf++ = key;
		key = kdb_handle_escape(buf, pbuf - buf);
		if (key < 0) /* no escape sequence; return best character */
			return buf[pbuf - buf == 2 ? 1 : 0];
		if (key > 0)
			return key;
	}

	unreachable();
}

/**
 * kdb_position_cursor() - Place cursor in the correct horizontal position
 * @prompt: Nil-terminated string containing the prompt string
 * @buffer: Nil-terminated string containing the entire command line
 * @cp: Cursor position, pointer the character in buffer where the cursor
 *      should be positioned.
 *
 * The cursor is positioned by sending a carriage-return and then printing
 * the content of the line until we reach the correct cursor position.
 *
 * There is some additional fine detail here.
 *
 * Firstly, even though kdb_printf() will correctly format zero-width fields
 * we want the second call to kdb_printf() to be conditional. That keeps things
 * a little cleaner when LOGGING=1.
 *
 * Secondly, we can't combine everything into one call to kdb_printf() since
 * that renders into a fixed length buffer and the combined print could result
 * in unwanted truncation.
 */
static void kdb_position_cursor(char *prompt, char *buffer, char *cp)
{
	kdb_printf("\r%s", prompt);
	if (cp > buffer)
		kdb_printf("%.*s", (int)(cp - buffer), buffer);
}

/*
 * kdb_read
 *
 *	This function reads a string of characters, terminated by
 *	a newline, or by reaching the end of the supplied buffer,
 *	from the current kernel debugger console device.
 * Parameters:
 *	buffer	- Address of character buffer to receive input characters.
 *	bufsize - size, in bytes, of the character buffer
 * Returns:
 *	Returns a pointer to the buffer containing the received
 *	character string.  This string will be terminated by a
 *	newline character.
 * Locking:
 *	No locks are required to be held upon entry to this
 *	function.  It is not reentrant - it relies on the fact
 *	that while kdb is running on only one "master debug" cpu.
 * Remarks:
 *	The buffer size must be >= 2.
 */

static char *kdb_read(char *buffer, size_t bufsize)
{
	char *cp = buffer;
	char *bufend = buffer+bufsize-2;	/* Reserve space for newline
						 * and null byte */
	char *lastchar;
	char *p_tmp;
	char tmp;
	static char tmpbuffer[CMD_BUFLEN];
	int len = strlen(buffer);
	int len_tmp;
	int tab = 0;
	int count;
	int i;
	int diag, dtab_count;
	int key, ret;

	diag = kdbgetintenv("DTABCOUNT", &dtab_count);
	if (diag)
		dtab_count = 30;

	if (len > 0) {
		cp += len;
		if (*(buffer+len-1) == '\n')
			cp--;
	}

	lastchar = cp;
	*cp = '\0';
	kdb_printf("%s", buffer);
poll_again:
	key = kdb_getchar();
	if (key != 9)
		tab = 0;
	switch (key) {
	case 8: /* backspace */
		if (cp > buffer) {
			memmove(cp-1, cp, lastchar - cp + 1);
			lastchar--;
			cp--;
			kdb_printf("\b%s ", cp);
			kdb_position_cursor(kdb_prompt_str, buffer, cp);
		}
		break;
	case 10: /* linefeed */
	case 13: /* carriage return */
		*lastchar++ = '\n';
		*lastchar++ = '\0';
		if (!KDB_STATE(KGDB_TRANS)) {
			KDB_STATE_SET(KGDB_TRANS);
			kdb_printf("%s", buffer);
		}
		kdb_printf("\n");
		return buffer;
	case 4: /* Del */
		if (cp < lastchar) {
			memmove(cp, cp+1, lastchar - cp);
			lastchar--;
			kdb_printf("%s ", cp);
			kdb_position_cursor(kdb_prompt_str, buffer, cp);
		}
		break;
	case 1: /* Home */
		if (cp > buffer) {
			cp = buffer;
			kdb_position_cursor(kdb_prompt_str, buffer, cp);
		}
		break;
	case 5: /* End */
		if (cp < lastchar) {
			kdb_printf("%s", cp);
			cp = lastchar;
		}
		break;
	case 2: /* Left */
		if (cp > buffer) {
			kdb_printf("\b");
			--cp;
		}
		break;
	case 14: /* Down */
	case 16: /* Up */
		kdb_printf("\r%*c\r",
			   (int)(strlen(kdb_prompt_str) + (lastchar - buffer)),
			   ' ');
		*lastchar = (char)key;
		*(lastchar+1) = '\0';
		return lastchar;
	case 6: /* Right */
		if (cp < lastchar) {
			kdb_printf("%c", *cp);
			++cp;
		}
		break;
	case 9: /* Tab */
		if (tab < 2)
			++tab;

		tmp = *cp;
		*cp = '\0';
		p_tmp = strrchr(buffer, ' ');
		p_tmp = (p_tmp ? p_tmp + 1 : buffer);
		strscpy(tmpbuffer, p_tmp);
		*cp = tmp;

		len = strlen(tmpbuffer);
		count = kallsyms_symbol_complete(tmpbuffer, sizeof(tmpbuffer));
		if (tab == 2 && count > 0) {
			kdb_printf("\n%d symbols are found.", count);
			if (count > dtab_count) {
				count = dtab_count;
				kdb_printf(" But only first %d symbols will"
					   " be printed.\nYou can change the"
					   " environment variable DTABCOUNT.",
					   count);
			}
			kdb_printf("\n");
			for (i = 0; i < count; i++) {
				ret = kallsyms_symbol_next(tmpbuffer, i, sizeof(tmpbuffer));
				if (WARN_ON(!ret))
					break;
				if (ret != -E2BIG)
					kdb_printf("%s ", tmpbuffer);
				else
					kdb_printf("%s... ", tmpbuffer);
				tmpbuffer[len] = '\0';
			}
			if (i >= dtab_count)
				kdb_printf("...");
			kdb_printf("\n");
			kdb_printf("%s",  kdb_prompt_str);
			kdb_printf("%s", buffer);
			if (cp != lastchar)
				kdb_position_cursor(kdb_prompt_str, buffer, cp);
		} else if (tab != 2 && count > 0) {
			/* How many new characters do we want from tmpbuffer? */
			len_tmp = strlen(tmpbuffer) - len;
			if (lastchar + len_tmp >= bufend)
				len_tmp = bufend - lastchar;

			if (len_tmp) {
				/* + 1 ensures the '\0' is memmove'd */
				memmove(cp+len_tmp, cp, (lastchar-cp) + 1);
				memcpy(cp, tmpbuffer+len, len_tmp);
				kdb_printf("%s", cp);
				cp += len_tmp;
				lastchar += len_tmp;
				if (cp != lastchar)
					kdb_position_cursor(kdb_prompt_str,
							    buffer, cp);
			}
		}
		kdb_nextline = 1; /* reset output line number */
		break;
	default:
		if (key >= 32 && lastchar < bufend) {
			if (cp < lastchar) {
				memmove(cp+1, cp, lastchar - cp + 1);
				lastchar++;
				*cp = key;
				kdb_printf("%s", cp);
				++cp;
				kdb_position_cursor(kdb_prompt_str, buffer, cp);
			} else {
				*++lastchar = '\0';
				*cp++ = key;
				/* The kgdb transition check will hide
				 * printed characters if we think that
				 * kgdb is connecting, until the check
				 * fails */
				if (!KDB_STATE(KGDB_TRANS)) {
					if (kgdb_transition_check(buffer))
						return buffer;
				} else {
					kdb_printf("%c", key);
				}
			}
			/* Special escape to kgdb */
			if (lastchar - buffer >= 5 &&
			    strcmp(lastchar - 5, "$?#3f") == 0) {
				kdb_gdb_state_pass(lastchar - 5);
				strcpy(buffer, "kgdb");
				KDB_STATE_SET(DOING_KGDB);
				return buffer;
			}
			if (lastchar - buffer >= 11 &&
			    strcmp(lastchar - 11, "$qSupported") == 0) {
				kdb_gdb_state_pass(lastchar - 11);
				strcpy(buffer, "kgdb");
				KDB_STATE_SET(DOING_KGDB);
				return buffer;
			}
		}
		break;
	}
	goto poll_again;
}

/*
 * kdb_getstr
 *
 *	Print the prompt string and read a command from the
 *	input device.
 *
 * Parameters:
 *	buffer	Address of buffer to receive command
 *	bufsize Size of buffer in bytes
 *	prompt	Pointer to string to use as prompt string
 * Returns:
 *	Pointer to command buffer.
 * Locking:
 *	None.
 * Remarks:
 *	For SMP kernels, the processor number will be
 *	substituted for %d, %x or %o in the prompt.
 */

char *kdb_getstr(char *buffer, size_t bufsize, const char *prompt)
{
	if (prompt && kdb_prompt_str != prompt)
		strscpy(kdb_prompt_str, prompt);
	kdb_printf("%s", kdb_prompt_str);
	kdb_nextline = 1;	/* Prompt and input resets line number */
	return kdb_read(buffer, bufsize);
}

/*
 * kdb_input_flush
 *
 *	Get rid of any buffered console input.
 *
 * Parameters:
 *	none
 * Returns:
 *	nothing
 * Locking:
 *	none
 * Remarks:
 *	Call this function whenever you want to flush input.  If there is any
 *	outstanding input, it ignores all characters until there has been no
 *	data for approximately 1ms.
 */

static void kdb_input_flush(void)
{
	get_char_func *f;
	int res;
	int flush_delay = 1;
	while (flush_delay) {
		flush_delay--;
empty:
		touch_nmi_watchdog();
		for (f = &kdb_poll_funcs[0]; *f; ++f) {
			res = (*f)();
			if (res != -1) {
				flush_delay = 1;
				goto empty;
			}
		}
		if (flush_delay)
			mdelay(1);
	}
}

/*
 * kdb_printf
 *
 *	Print a string to the output device(s).
 *
 * Parameters:
 *	printf-like format and optional args.
 * Returns:
 *	0
 * Locking:
 *	None.
 * Remarks:
 *	use 'kdbcons->write()' to avoid polluting 'log_buf' with
 *	kdb output.
 *
 *  If the user is doing a cmd args | grep srch
 *  then kdb_grepping_flag is set.
 *  In that case we need to accumulate full lines (ending in \n) before
 *  searching for the pattern.
 */

static char kdb_buffer[256];	/* A bit too big to go on stack */
static char *next_avail = kdb_buffer;
static int  size_avail;
static int  suspend_grep;

/*
 * search arg1 to see if it contains arg2
 * (kdmain.c provides flags for ^pat and pat$)
 *
 * return 1 for found, 0 for not found
 */
static int kdb_search_string(char *searched, char *searchfor)
{
	char firstchar, *cp;
	int len1, len2;

	/* not counting the newline at the end of "searched" */
	len1 = strlen(searched)-1;
	len2 = strlen(searchfor);
	if (len1 < len2)
		return 0;
	if (kdb_grep_leading && kdb_grep_trailing && len1 != len2)
		return 0;
	if (kdb_grep_leading) {
		if (!strncmp(searched, searchfor, len2))
			return 1;
	} else if (kdb_grep_trailing) {
		if (!strncmp(searched+len1-len2, searchfor, len2))
			return 1;
	} else {
		firstchar = *searchfor;
		cp = searched;
		while ((cp = strchr(cp, firstchar))) {
			if (!strncmp(cp, searchfor, len2))
				return 1;
			cp++;
		}
	}
	return 0;
}

static void kdb_msg_write(const char *msg, int msg_len)
{
	struct console *c;
	const char *cp;
	int cookie;
	int len;

	if (msg_len == 0)
		return;

	cp = msg;
	len = msg_len;

	while (len--) {
		dbg_io_ops->write_char(*cp);
		cp++;
	}

	/*
	 * The console_srcu_read_lock() only provides safe console list
	 * traversal. The use of the ->write() callback relies on all other
	 * CPUs being stopped at the moment and console drivers being able to
	 * handle reentrance when @oops_in_progress is set.
	 *
	 * There is no guarantee that every console driver can handle
	 * reentrance in this way; the developer deploying the debugger
	 * is responsible for ensuring that the console drivers they
	 * have selected handle reentrance appropriately.
	 */
	cookie = console_srcu_read_lock();
	for_each_console_srcu(c) {
		short flags = console_srcu_read_flags(c);

		if (!console_is_usable(c, flags, true))
			continue;
		if (c == dbg_io_ops->cons)
			continue;

		if (flags & CON_NBCON) {
			struct nbcon_write_context wctxt = { };

			/*
			 * Do not continue if the console is NBCON and the context
			 * can't be acquired.
			 */
			if (!nbcon_kdb_try_acquire(c, &wctxt))
				continue;

			nbcon_write_context_set_buf(&wctxt, (char *)msg, msg_len);

			c->write_atomic(c, &wctxt);
			nbcon_kdb_release(&wctxt);
		} else {
			/*
			 * Set oops_in_progress to encourage the console drivers to
			 * disregard their internal spin locks: in the current calling
			 * context the risk of deadlock is a bigger problem than risks
			 * due to re-entering the console driver. We operate directly on
			 * oops_in_progress rather than using bust_spinlocks() because
			 * the calls bust_spinlocks() makes on exit are not appropriate
			 * for this calling context.
			 */
			++oops_in_progress;
			c->write(c, msg, msg_len);
			--oops_in_progress;
		}
		touch_nmi_watchdog();
	}
	console_srcu_read_unlock(cookie);
}

int vkdb_printf(enum kdb_msgsrc src, const char *fmt, va_list ap)
{
	int diag;
	int linecount;
	int colcount;
	int logging, saved_loglevel = 0;
	int retlen = 0;
	int fnd, len;
	int this_cpu, old_cpu;
	char *cp, *cp2, *cphold = NULL, replaced_byte = ' ';
	char *moreprompt = "more> ";
	unsigned long flags;

	/* Serialize kdb_printf if multiple cpus try to write at once.
	 * But if any cpu goes recursive in kdb, just print the output,
	 * even if it is interleaved with any other text.
	 */
	local_irq_save(flags);
	this_cpu = smp_processor_id();
	for (;;) {
		old_cpu = cmpxchg(&kdb_printf_cpu, -1, this_cpu);
		if (old_cpu == -1 || old_cpu == this_cpu)
			break;

		cpu_relax();
	}

	diag = kdbgetintenv("LINES", &linecount);
	if (diag || linecount <= 1)
		linecount = 24;

	diag = kdbgetintenv("COLUMNS", &colcount);
	if (diag || colcount <= 1)
		colcount = 80;

	diag = kdbgetintenv("LOGGING", &logging);
	if (diag)
		logging = 0;

	if (!kdb_grepping_flag || suspend_grep) {
		/* normally, every vsnprintf starts a new buffer */
		next_avail = kdb_buffer;
		size_avail = sizeof(kdb_buffer);
	}
	vsnprintf(next_avail, size_avail, fmt, ap);

	/*
	 * If kdb_parse() found that the command was cmd xxx | grep yyy
	 * then kdb_grepping_flag is set, and kdb_grep_string contains yyy
	 *
	 * Accumulate the print data up to a newline before searching it.
	 * (vsnprintf does null-terminate the string that it generates)
	 */

	/* skip the search if prints are temporarily unconditional */
	if (!suspend_grep && kdb_grepping_flag) {
		cp = strchr(kdb_buffer, '\n');
		if (!cp) {
			/*
			 * Special cases that don't end with newlines
			 * but should be written without one:
			 *   The "[nn]kdb> " prompt should
			 *   appear at the front of the buffer.
			 *
			 *   The "[nn]more " prompt should also be
			 *     (MOREPROMPT -> moreprompt)
			 *   written *   but we print that ourselves,
			 *   we set the suspend_grep flag to make
			 *   it unconditional.
			 *
			 */
			if (next_avail == kdb_buffer) {
				/*
				 * these should occur after a newline,
				 * so they will be at the front of the
				 * buffer
				 */
				cp2 = kdb_buffer;
				len = strlen(kdb_prompt_str);
				if (!strncmp(cp2, kdb_prompt_str, len)) {
					/*
					 * We're about to start a new
					 * command, so we can go back
					 * to normal mode.
					 */
					kdb_grepping_flag = 0;
					goto kdb_printit;
				}
			}
			/* no newline; don't search/write the buffer
			   until one is there */
			len = strlen(kdb_buffer);
			next_avail = kdb_buffer + len;
			size_avail = sizeof(kdb_buffer) - len;
			goto kdb_print_out;
		}

		/*
		 * The newline is present; print through it or discard
		 * it, depending on the results of the search.
		 */
		cp++;	 	     /* to byte after the newline */
		replaced_byte = *cp; /* remember what it was */
		cphold = cp;	     /* remember where it was */
		*cp = '\0';	     /* end the string for our search */

		/*
		 * We now have a newline at the end of the string
		 * Only continue with this output if it contains the
		 * search string.
		 */
		fnd = kdb_search_string(kdb_buffer, kdb_grep_string);
		if (!fnd) {
			/*
			 * At this point the complete line at the start
			 * of kdb_buffer can be discarded, as it does
			 * not contain what the user is looking for.
			 * Shift the buffer left.
			 */
			*cphold = replaced_byte;
			len = strlen(cphold);
			/* Use memmove() because the buffers overlap */
			memmove(kdb_buffer, cphold, len + 1);
			next_avail = kdb_buffer + len;
			size_avail = sizeof(kdb_buffer) - len;
			goto kdb_print_out;
		}
		if (kdb_grepping_flag >= KDB_GREPPING_FLAG_SEARCH) {
			/*
			 * This was a interactive search (using '/' at more
			 * prompt) and it has completed. Replace the \0 with
			 * its original value to ensure multi-line strings
			 * are handled properly, and return to normal mode.
			 */
			*cphold = replaced_byte;
			kdb_grepping_flag = 0;
		}
		/*
		 * at this point the string is a full line and
		 * should be printed, up to the null.
		 */
	}
kdb_printit:

	/*
	 * Write to all consoles.
	 */
	retlen = strlen(kdb_buffer);
	cp = (char *) printk_skip_headers(kdb_buffer);
	if (!dbg_kdb_mode && kgdb_connected)
		gdbstub_msg_write(cp, retlen - (cp - kdb_buffer));
	else
		kdb_msg_write(cp, retlen - (cp - kdb_buffer));

	if (logging) {
		saved_loglevel = console_loglevel;
		console_loglevel = CONSOLE_LOGLEVEL_SILENT;
		if (printk_get_level(kdb_buffer) || src == KDB_MSGSRC_PRINTK)
			printk("%s", kdb_buffer);
		else
			pr_info("%s", kdb_buffer);
	}

	if (KDB_STATE(PAGER)) {
		/*
		 * Check printed string to decide how to bump the
		 * kdb_nextline to control when the more prompt should
		 * show up.
		 */
		int got = 0;
		len = retlen;
		while (len--) {
			if (kdb_buffer[len] == '\n') {
				kdb_nextline++;
				got = 0;
			} else if (kdb_buffer[len] == '\r') {
				got = 0;
			} else {
				got++;
			}
		}
		kdb_nextline += got / (colcount + 1);
	}

	/* check for having reached the LINES number of printed lines */
	if (kdb_nextline >= linecount) {
		char ch;

		/* Watch out for recursion here.  Any routine that calls
		 * kdb_printf will come back through here.  And kdb_read
		 * uses kdb_printf to echo on serial consoles ...
		 */
		kdb_nextline = 1;	/* In case of recursion */

		/*
		 * Pause until cr.
		 */
		moreprompt = kdbgetenv("MOREPROMPT");
		if (moreprompt == NULL)
			moreprompt = "more> ";

		kdb_input_flush();
		kdb_msg_write(moreprompt, strlen(moreprompt));

		if (logging)
			printk("%s", moreprompt);

		ch = kdb_getchar();
		kdb_nextline = 1;	/* Really set output line 1 */

		/* empty and reset the buffer: */
		kdb_buffer[0] = '\0';
		next_avail = kdb_buffer;
		size_avail = sizeof(kdb_buffer);
		if ((ch == 'q') || (ch == 'Q')) {
			/* user hit q or Q */
			KDB_FLAG_SET(CMD_INTERRUPT); /* command interrupted */
			KDB_STATE_CLEAR(PAGER);
			/* end of command output; back to normal mode */
			kdb_grepping_flag = 0;
			kdb_printf("\n");
		} else if (ch == ' ') {
			kdb_printf("\r");
			suspend_grep = 1; /* for this recursion */
		} else if (ch == '\n' || ch == '\r') {
			kdb_nextline = linecount - 1;
			kdb_printf("\r");
			suspend_grep = 1; /* for this recursion */
		} else if (ch == '/' && !kdb_grepping_flag) {
			kdb_printf("\r");
			kdb_getstr(kdb_grep_string, KDB_GREP_STRLEN,
				   kdbgetenv("SEARCHPROMPT") ?: "search> ");
			*strchrnul(kdb_grep_string, '\n') = '\0';
			kdb_grepping_flag += KDB_GREPPING_FLAG_SEARCH;
			suspend_grep = 1; /* for this recursion */
		} else if (ch) {
			/* user hit something unexpected */
			suspend_grep = 1; /* for this recursion */
			if (ch != '/')
				kdb_printf(
				    "\nOnly 'q', 'Q' or '/' are processed at "
				    "more prompt, input ignored\n");
			else
				kdb_printf("\n'/' cannot be used during | "
					   "grep filtering, input ignored\n");
		} else if (kdb_grepping_flag) {
			/* user hit enter */
			suspend_grep = 1; /* for this recursion */
			kdb_printf("\n");
		}
		kdb_input_flush();
	}

	/*
	 * For grep searches, shift the printed string left.
	 *  replaced_byte contains the character that was overwritten with
	 *  the terminating null, and cphold points to the null.
	 * Then adjust the notion of available space in the buffer.
	 */
	if (kdb_grepping_flag && !suspend_grep) {
		*cphold = replaced_byte;
		len = strlen(cphold);
		/* Use memmove() because the buffers overlap */
		memmove(kdb_buffer, cphold, len + 1);
		next_avail = kdb_buffer + len;
		size_avail = sizeof(kdb_buffer) - len;
	}

kdb_print_out:
	suspend_grep = 0; /* end of what may have been a recursive call */
	if (logging)
		console_loglevel = saved_loglevel;
	/* kdb_printf_cpu locked the code above. */
	smp_store_release(&kdb_printf_cpu, old_cpu);
	local_irq_restore(flags);
	return retlen;
}

int kdb_printf(const char *fmt, ...)
{
	va_list ap;
	int r;

	va_start(ap, fmt);
	r = vkdb_printf(KDB_MSGSRC_INTERNAL, fmt, ap);
	va_end(ap);

	return r;
}
EXPORT_SYMBOL_GPL(kdb_printf);