> +/* The various types of throttling algorithms */
> +enum iothrottle_strategy {
> + IOTHROTTLE_LEAKY_BUCKET,
It's better to explicitly assigned 0 to IOTHROTTLE_LEAKY_BUCKET.
> + IOTHROTTLE_TOKEN_BUCKET,
> +};
> +static int iothrottle_parse_args(char *buf, size_t nbytes, dev_t *dev,
> + u64 *iorate,
> + enum iothrottle_strategy *strategy,
> + s64 *bucket_size)
> +{
> + char *p = buf;
> + int count = 0;
> + char *s[3];
> + unsigned long strategy_val;
> + int ret;
> +
> + /* split the colon-delimited input string into its elements */
> + memset(s, 0, sizeof(s));
> + while (count < ARRAY_SIZE(s)) {
> + p = memchr(p, ':', buf + nbytes - p);
> + if (!p)
> + break;
> + *p++ = '\0';
> + if (p >= buf + nbytes)
> + break;
> + s[count++] = p;
> + }
use strsep()
> +
> + /* i/o bandwidth limit */
> + if (!s[0])
> + return -EINVAL;
> + ret = strict_strtoull(s[0], 10, iorate);
> + if (ret < 0)
> + return ret;
> + if (!*iorate) {
> + /*
> + * we're deleting a limiting rule, so just ignore the other
> + * parameters
> + */
> + *strategy = 0;
> + *bucket_size = 0;
> + goto out;
> + }
> + *iorate = ALIGN(*iorate, 1024);
> +
> + /* throttling strategy */
> + if (!s[1])
> + return -EINVAL;
> + ret = strict_strtoul(s[1], 10, &strategy_val);
> + if (ret < 0)
> + return ret;
> + *strategy = (enum iothrottle_strategy)strategy_val;
> + switch (*strategy) {
> + case IOTHROTTLE_LEAKY_BUCKET:
> + /* leaky bucket ignores bucket size */
> + *bucket_size = 0;
> + goto out;
> + case IOTHROTTLE_TOKEN_BUCKET:
> + break;
> + default:
> + return -EINVAL;
> + }
> +
> + /* bucket size */
> + if (!s[2])
> + return -EINVAL;
> + ret = strict_strtoll(s[2], 10, bucket_size);
> + if (ret < 0)
> + return ret;
> + if (*bucket_size < 0)
> + return -EINVAL;
> + *bucket_size = ALIGN(*bucket_size, 1024);
> +out:
> +
> + /* block device number */
> + *dev = devname2dev_t(buf);
why not parse dev before parse bandwidth limit ?
> + return *dev ? 0 : -EINVAL;
> +}
> +
> +static int iothrottle_write(struct cgroup *cgrp, struct cftype *cft,
> + const char *buffer)
> +{
> + struct iothrottle *iot;
> + struct iothrottle_node *n, *newn = NULL;
> + dev_t dev;
> + u64 iorate;
> + enum iothrottle_strategy strategy;
> + s64 bucket_size;
> + char *buf;
> + size_t nbytes = strlen(buffer);
> + int ret = 0;
> +
> + buf = kmalloc(nbytes + 1, GFP_KERNEL);
> + if (!buf)
> + return -ENOMEM;
> + memcpy(buf, buffer, nbytes + 1);
> +
redundant kmalloc, just use buffer, and ...
> + ret = iothrottle_parse_args(buf, nbytes, &dev, &iorate,
> + &strategy, &bucket_size);
> + if (ret)
> + goto out1;
> + if (iorate) {
> + newn = kmalloc(sizeof(*newn), GFP_KERNEL);
> + if (!newn) {
> + ret = -ENOMEM;
> + goto out1;
> + }
> + newn->dev = dev;
> + newn->iorate = iorate;
> + newn->strategy = strategy;
> + newn->bucket_size = bucket_size;
> + newn->timestamp = jiffies;
> + atomic_long_set(&newn->stat, 0);
> + atomic_long_set(&newn->token, 0);
> + }
> + if (!cgroup_lock_live_group(cgrp)) {
> + kfree(newn);
> + ret = -ENODEV;
> + goto out1;
> + }
> + iot = cgroup_to_iothrottle(cgrp);
> +
> + spin_lock(&iot->lock);
> + if (!iorate) {
> + /* Delete a block device limiting rule */
> + n = iothrottle_delete_node(iot, dev);
> + goto out2;
> + }
> + n = iothrottle_search_node(iot, dev);
> + if (n) {
> + /* Update a block device limiting rule */
> + iothrottle_replace_node(iot, n, newn);
> + goto out2;
> + }
> + /* Add a new block device limiting rule */
> + iothrottle_insert_node(iot, newn);
> +out2:
> + spin_unlock(&iot->lock);
> + cgroup_unlock();
> + if (n) {
> + synchronize_rcu();
> + kfree(n);
> + }
> +out1:
> + kfree(buf);
> + return ret;
> +}
> +
> +static struct cftype files[] = {
> + {
> + .name = "bandwidth",
> + .read_seq_string = iothrottle_read,
> + .write_string = iothrottle_write,
and you should specify .max_write_len = XXX unless XXX <= 64.
You use 1024 in v4.
> + },
> +};
> +
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