On Mon, 2017-10-02 at 12:27 +0200, Florian Westphal wrote:
> Device alias can be set by either rtnetlink (rtnl is held) or sysfs.
>
> rtnetlink hold the rtnl mutex, sysfs acquires it for this purpose.
> Add an extra mutex for it plus a seqcount to get a consistent snapshot
> of the alias buffer.
> +int dev_get_alias(const struct net_device *dev, char *alias, size_t len)
> +{
> + unsigned int seq;
> + int ret;
> +
> + for (;;) {
> + const char *name;
> +
> + ret = 0;
> + rcu_read_lock();
> + name = rcu_dereference(dev->ifalias);
> + seq = raw_seqcount_begin(&ifalias_rename_seq);
> + if (name)
> + ret = snprintf(alias, len, "%s", name);
> + rcu_read_unlock();
> +
> + if (!read_seqcount_retry(&ifalias_rename_seq, seq))
> + break;
> +
> + cond_resched();
> + }
> +
> + return ret;
> +}
I believe this too complex and not needed.
Just use RCU : A writer is supposed to work on a private copy, and
_then_ publish the new pointer, so that a reader can not see mangled
string.
We either copy the 'old' name or the 'new' one.
A seqcount is not needed, and wont prevent you from reading the value
right before a change anyway.
