On 10/1/19 8:27 PM, Douglas Gilbert wrote:
- kt = ns_to_ktime((u64)delta_jiff * (NSEC_PER_SEC / HZ));
- } else
- kt = ndelay;
+ u64 ns = jiffies_to_nsecs(delta_jiff);
+
+ if (sdebug_random && ns < U32_MAX) {
+ ns = prandom_u32_max((u32)ns);
+ } else if (sdebug_random) {
+ ns >>= 12; /* scale to 4 usec precision */
+ if (ns < U32_MAX) /* over 4 hours max */
+ ns = prandom_u32_max((u32)ns);
+ ns <<= 12;
An explanation of how the scaling factor has been chosen is missing.
Is it user friendly to disable randomization silently if delta_jiff
exceeds a certain value? How about restricting delta_jiff to e.g. ten
times the SCSI timeout?
+ } else { /* ndelay has a 4.2 second max */
+ kt = sdebug_random ? prandom_u32_max((u32)ndelay) :
+ (u32)ndelay;
+ }
Are these (u32) casts necessary?
+static ssize_t random_show(struct device_driver *ddp, char *buf)
+{
+ return scnprintf(buf, PAGE_SIZE, "%d\n", (int)sdebug_random);
+}
Is the (int) cast necessary?
+static ssize_t random_store(struct device_driver *ddp, const char *buf,
+ size_t count)
+{
+ int n;
+
+ if (count > 0 && kstrtoint(buf, 10, &n) == 0 && n >= 0) {
+ sdebug_random = (n > 0);
+ return count;
+ }
+ return -EINVAL;
+}
+static DRIVER_ATTR_RW(random);
Is the "count > 0" check useful? I don't think that sysfs ever passes
count == 0 to store callback functions.
Thanks,
Bart.
