[PATCHv5 bpf-next 4/9] ftrace: Add update_ftrace_direct_add function

[Jiri Olsa]

On Wed, Dec 17, 2025 at 08:39:09PM -0500, Steven Rostedt wrote:
> On Mon, 15 Dec 2025 22:13:57 +0100
> Jiri Olsa <jolsa at kernel.org> wrote:
> 
> 
> > +/**
> > + * hash_add - adds two struct ftrace_hash and returns the result
> > + * @a: struct ftrace_hash object
> > + * @b: struct ftrace_hash object
> > + *
> > + * Returns struct ftrace_hash object on success, NULL on error.
> > + */
> > +static struct ftrace_hash *hash_add(struct ftrace_hash *a, struct ftrace_hash *b)
> > +{
> > +	struct ftrace_func_entry *entry;
> > +	struct ftrace_hash *add;
> > +	int size, i;
> > +
> > +	size = hash_count(a) + hash_count(b);
> > +	if (size > 32)
> > +		size = 32;
> > +
> > +	add = alloc_and_copy_ftrace_hash(fls(size), a);
> > +	if (!add)
> > +		goto error;
> 
> You can just return NULL here, as add is NULL.

ok

> 
> > +
> > +	size = 1 << b->size_bits;
> > +	for (i = 0; i < size; i++) {
> > +		hlist_for_each_entry(entry, &b->buckets[i], hlist) {
> > +			if (add_hash_entry_direct(add, entry->ip, entry->direct) == NULL)
> > +				goto error;
> 
> Could remove the error and have:
> 
> 			if (add_hash_entry_direct(add, entry->ip, entry->direct) == NULL) {
> 				free_ftrace_hash(add);
> 				return NULL;
> 			}

ok

> 
> 
> > +		}
> > +	}
> > +	return add;
> > +
> > + error:
> > +	free_ftrace_hash(add);
> > +	return NULL;
> > +}
> > +
> 
> Non static functions require a kerneldoc header.

ah right, will add

> 
> > +int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash)
> > +{
> > +	struct ftrace_hash *old_direct_functions = NULL, *new_direct_functions;
> > +	struct ftrace_hash *old_filter_hash, *new_filter_hash = NULL;
> 
> BTW, I prefer to not double up on variables. That is to have each on
> their own lines. Makes it easier to read for me.
> 
> > +	struct ftrace_func_entry *entry;
> > +	int i, size, err = -EINVAL;
> 
> Even here.

ok, will split

> 
> > +	bool reg;
> > +
> > +	if (!hash_count(hash))
> > +		return -EINVAL;
> > +
> > +	mutex_lock(&direct_mutex);
> > +
> > +	/* Make sure requested entries are not already registered. */
> > +	size = 1 << hash->size_bits;
> > +	for (i = 0; i < size; i++) {
> 
> If you want, you can remove the i declaration and use for(int i = 0; ... here.

ok

SNIP

> > +	}
> > +
> > +	if (err) {
> > +		/* reset direct_functions and free the new one */
> > +		rcu_assign_pointer(direct_functions, old_direct_functions);
> > +		old_direct_functions = new_direct_functions;
> > +	}
> > +
> > + out_unlock:
> > +	mutex_unlock(&direct_mutex);
> > +
> > +	if (old_direct_functions && old_direct_functions != EMPTY_HASH)
> > +		call_rcu_tasks(&old_direct_functions->rcu, register_ftrace_direct_cb);
> > +	if (new_filter_hash)
> 
> free_ftrace_hash() checks for NULL, so you don't need the above if statement.

ok

thanks,
jirka