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

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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: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
This commit is contained in:
Miguel Ojeda 2018-02-27 23:09:52 +01:00
parent 2e8c04f757
commit b34050fadb
1 changed files with 78 additions and 17 deletions
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95
drivers/auxdisplay/charlcd.c
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@ -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;
/* If the command is valid, move to the new address */
if (parse_xy(esc, &priv->addr.x, &priv->addr.y))
charlcd_gotoxy(lcd);
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;
}
}
charlcd_gotoxy(lcd);
/* Regardless of its validity, mark as processed */
processed = 1;
break;
}