linux-kernel - Re: [PATCH] net: caif: Don't act on notification for non-caif devices

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Date:	Tue, 24 Jan 2012 10:23:26 -0500
From:	Sasha Levin <levinsasha928@...il.com>
To:	Sjur Brændeland <sjurbren@...il.com>
Cc:	davem@...emloft.net, davej@...hat.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: caif: Don't act on notification for non-caif devices

On Tue, Jan 24, 2012 at 10:06 AM, Sjur Brændeland <sjurbren@...il.com> wrote:
> Hi Sasha,
>
>>> Nack, we have to handle other device types than just ARPHDR_CAIF after
>>> introducing CAIF over USB/NCM.
>> What my patch did was simply move the type check to above the net_generic call,
>> it didn't add any new checks - which according to what you said, you'll need to do anyway.
>
> As I said I, don't think your patch would work. Try to see what happens if
> dev->type != ARPHDR_CAIF and caifd != NULL. Then the statement:
>
>        if (caifd == NULL && dev->type != ARPHRD_CAIF)
>                return 0;
> is very different from:
>
>       if (dev->type != ARPHRD_CAIF)
>               return 0;
> ...
>       if (caifd == NULL)
>               return 0;

Right.

> Anyway, another option could be to explicitly check if name space is
> initialized,
> similar to what net_generic() does,e.g. something like:
>
> diff --git a/net/caif/caif_dev.c b/net/caif/caif_dev.c
> index 673728a..3197bc2 100644
> --- a/net/caif/caif_dev.c
> +++ b/net/caif/caif_dev.c
> @@ -371,6 +371,13 @@ static int caif_device_notify(struct notifier_block *me, un
>        struct cflayer *layer, *link_support;
>        int head_room = 0;
>        struct caif_device_entry_list *caifdevs;
> +       int len;
> +
> +       rcu_read_lock();
> +       len = rcu_dereference(dev_net(dev)->gen)->len;
> +       rcu_read_unlock();
> +       if (caif_net_id > len)
> +               return 0;
>
>        cfg = get_cfcnfg(dev_net(dev));
>        caifdevs = caif_device_list(dev_net(dev));

We could, in that case we'd just need to handle the case where it was
initialized by a device with higher id than CAIF (which we already do
I think), and do it without touching net_generic structure directly.

btw, Why do we store the devices per-namespace instead of globally? Is
it such a big benefit in performance?
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