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Commit b34050fa authored by Miguel Ojeda's avatar Miguel Ojeda
Browse files

auxdisplay: charlcd: Fix and clean up handling of x/y commands 



The current version is not parsing multiple x/y commands as the code
originally intended. On top of that, kstrtoul() expects
NULL-terminated strings. Finally, the code does two passes over
the string.

Some explanations about the supported syntax are added as well.

Cc: Willy Tarreau <w@1wt.eu>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Robert Abel <rabel@robertabel.eu>
Signed-off-by: default avatarMiguel Ojeda <miguel.ojeda.sandonis@gmail.com>
parent 2e8c04f7

drivers/auxdisplay/charlcd.c

+78 −17
Original line number Diff line number Diff line
@@ -11,6 +11,7 @@ 
 */



#include <linux/atomic.h>

#include <linux/ctype.h>

#include <linux/delay.h>

#include <linux/fs.h>

#include <linux/miscdevice.h>
@@ -293,6 +294,79 @@ static int charlcd_init_display(struct charlcd *lcd) 
	return 0;

}



/*

 * Parses an unsigned integer from a string, until a non-digit character

 * is found. The empty string is not accepted. No overflow checks are done.

 *

 * Returns whether the parsing was successful. Only in that case

 * the output parameters are written to.

 *

 * TODO: If the kernel adds an inplace version of kstrtoul(), this function

 * could be easily replaced by that.

 */

static bool parse_n(const char *s, unsigned long *res, const char **next_s)

{

	if (!isdigit(*s))

		return false;



	*res = 0;

	while (isdigit(*s)) {

		*res = *res * 10 + (*s - '0');

		++s;

	}



	*next_s = s;

	return true;

}



/*

 * Parses a movement command of the form "(.*);", where the group can be

 * any number of subcommands of the form "(x|y)[0-9]+".

 *

 * Returns whether the command is valid. The position arguments are

 * only written if the parsing was successful.

 *

 * For instance:

 *   - ";"          returns (<original x>, <original y>).

 *   - "x1;"        returns (1, <original y>).

 *   - "y2x1;"      returns (1, 2).

 *   - "x12y34x56;" returns (56, 34).

 *   - ""           fails.

 *   - "x"          fails.

 *   - "x;"         fails.

 *   - "x1"         fails.

 *   - "xy12;"      fails.

 *   - "x12yy12;"   fails.

 *   - "xx"         fails.

 */

static bool parse_xy(const char *s, unsigned long *x, unsigned long *y)

{

	unsigned long new_x = *x;

	unsigned long new_y = *y;



	for (;;) {

		if (!*s)

			return false;



		if (*s == ';')

			break;



		if (*s == 'x') {

			if (!parse_n(s + 1, &new_x, &s))

				return false;

		} else if (*s == 'y') {

			if (!parse_n(s + 1, &new_y, &s))

				return false;

		} else {

			return false;

		}

	}



	*x = new_x;

	*y = new_y;

	return true;

}



/*

 * These are the file operation function for user access to /dev/lcd

 * This function can also be called from inside the kernel, by
@@ -471,24 +545,11 @@ static inline int handle_lcd_special_code(struct charlcd *lcd) 
	}

	case 'x':	/* gotoxy : LxXXX[yYYY]; */

	case 'y':	/* gotoxy : LyYYY[xXXX]; */

		if (!strchr(esc, ';'))

			break;



		while (*esc) {

			if (*esc == 'x') {

				esc++;

				if (kstrtoul(esc, 10, &priv->addr.x) < 0)

					break;

			} else if (*esc == 'y') {

				esc++;

				if (kstrtoul(esc, 10, &priv->addr.y) < 0)

					break;

			} else {

				break;

			}

		}



		/* If the command is valid, move to the new address */

		if (parse_xy(esc, &priv->addr.x, &priv->addr.y))

			charlcd_gotoxy(lcd);



		/* Regardless of its validity, mark as processed */

		processed = 1;

		break;

	}