netdev - Re: [PATCH net-next 02/11] net: Introduce new api for walking upper and lower devices

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Date:   Thu, 13 Oct 2016 09:30:29 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     David Ahern <dsa@...ulusnetworks.com>
Cc:     jiri@...lanox.com, netdev@...r.kernel.org, davem@...emloft.net,
        dledford@...hat.com, sean.hefty@...el.com,
        hal.rosenstock@...il.com, linux-rdma@...r.kernel.org,
        j.vosburgh@...il.com, vfalico@...il.com, andy@...yhouse.net,
        jeffrey.t.kirsher@...el.com, intel-wired-lan@...ts.osuosl.org
Subject: Re: [PATCH net-next 02/11] net: Introduce new api for walking upper
 and lower devices

Wed, Oct 12, 2016 at 10:51:50PM CEST, dsa@...ulusnetworks.com wrote:
>This patch introduces netdev_walk_all_upper_dev_rcu,
>netdev_walk_all_lower_dev and netdev_walk_all_lower_dev_rcu. These
>functions recursively walk the adj_list of devices to determine all upper
>and lower devices.
>
>The functions take a callback function that is invoked for each device
>in the list. If the callback returns non-0, the walk is terminated and
>the functions return that code back to callers.
>
>Signed-off-by: David Ahern <dsa@...ulusnetworks.com>

[...]

>+int netdev_walk_all_lower_dev(struct net_device *dev,
>+			      int (*fn)(struct net_device *dev,
>+					void *data),
>+			      void *data)
>+{
>+	struct list_head *iter;
>+	struct net_device *ldev;
>+	int ret;
>+
>+	for (iter = &(dev)->adj_list.lower,
>+	     ldev = netdev_next_lower_dev(dev, &(iter));
>+	     ldev;
>+	     ldev = netdev_next_lower_dev(dev, &(iter))) {
>+		/* first is the lower device itself */
>+		ret = fn(ldev, data);
>+		if (ret)
>+			return ret;
>+
>+		/* then look at all of its lower devices */
>+		ret = netdev_walk_all_lower_dev(ldev, fn, data);

I believe that Veaceslav's reason to collapse the upper/lower trees was
to avoid this recursivity. I also believe that the recursivity was a big
issue for DaveM and BenH. Something changed?