md: factor out parsing of fixed-point numbers

safe_delay_store can parse fixed point numbers (for fractions
of a second).  We will want to do that for another sysfs
file soon, so factor out the code.

Signed-off-by: NeilBrown <neilb@suse.de>

1 files changed, 42 insertions, 22 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index c56c64d13075..93287f88f1f4 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -2763,6 +2763,47 @@ static void analyze_sbs(mddev_t * mddev)
         }
 }
 
+/* Read a fixed-point number.
+ * Numbers in sysfs attributes should be in "standard" units where
+ * possible, so time should be in seconds.
+ * However we internally use a a much smaller unit such as 
+ * milliseconds or jiffies.
+ * This function takes a decimal number with a possible fractional
+ * component, and produces an integer which is the result of
+ * multiplying that number by 10^'scale'.
+ * all without any floating-point arithmetic.
+ */
+int strict_strtoul_scaled(const char *cp, unsigned long *res, int scale)
+{
+        unsigned long result = 0;
+        long decimals = -1;
+        while (isdigit(*cp) || (*cp == '.' && decimals < 0)) {
+                if (*cp == '.')
+                        decimals = 0;
+                else if (decimals < scale) {
+                        unsigned int value;
+                        value = *cp - '0';
+                        result = result * 10 + value;
+                        if (decimals >= 0)
+                                decimals++;
+                }
+                cp++;
+        }
+        if (*cp == '\n')
+                cp++;
+        if (*cp)
+                return -EINVAL;
+        if (decimals < 0)
+                decimals = 0;
+        while (decimals < scale) {
+                result *= 10;
+                decimals ++;
+        }
+        *res = result;
+        return 0;
+}
+
+
 static void md_safemode_timeout(unsigned long data);
 
 static ssize_t
@@ -2774,31 +2815,10 @@ safe_delay_show(mddev_t *mddev, char *page)
 static ssize_t
 safe_delay_store(mddev_t *mddev, const char *cbuf, size_t len)
 {
-        int scale=1;
-        int dot=0;
-        int i;
         unsigned long msec;
-        char buf[30];
 
-        /* remove a period, and count digits after it */
-        if (len >= sizeof(buf))
-                return -EINVAL;
-        strlcpy(buf, cbuf, sizeof(buf));
-        for (i=0; i<len; i++) {
-                if (dot) {
-                        if (isdigit(buf[i])) {
-                                buf[i-1] = buf[i];
-                                scale *= 10;
-                        }
-                        buf[i] = 0;
-                } else if (buf[i] == '.') {
-                        dot=1;
-                        buf[i] = 0;
-                }
-        }
-        if (strict_strtoul(buf, 10, &msec) < 0)
+        if (strict_strtoul_scaled(cbuf, &msec, 3) < 0)
                 return -EINVAL;
-        msec = (msec * 1000) / scale;
         if (msec == 0)
                 mddev->safemode_delay = 0;
         else {