netdev - Re: [PATCH net-next v3 0/7] switchdev: add IPv4 routing offload

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Message-ID: <CAE4R7bDBJye388V+itU9XqFNjruf0GcbXWFydx60fghiZp+NQw@mail.gmail.com>
Date:	Tue, 3 Mar 2015 23:28:06 -0800
From:	Scott Feldman <sfeldma@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	Netdev <netdev@...r.kernel.org>,
	Jiří Pírko <jiri@...nulli.us>,
	Roopa Prabhu <roopa@...ulusnetworks.com>
Subject: Re: [PATCH net-next v3 0/7] switchdev: add IPv4 routing offload

On Tue, Mar 3, 2015 at 9:38 PM, David Miller <davem@...emloft.net> wrote:
> From: sfeldma@...il.com
> Date: Tue,  3 Mar 2015 15:31:53 -0800
>
>> v3:
>>
>> Changes based on v2 review comments:
>>
>>   - Move check for custom rules up earlier in patch set, to keep git bisect
>>     safe.
>>   - Simplify the route add/modify failure handling to simple try until
>>     failure, and then on failure, undo everything.  The switchdev driver
>>     will return err when route can normally be installed to device, but
>>     the install fails for one reason or another (no space left on device,
>>     etc).  If a failure happens, uninstall all routes from the device,
>>     punting forwarding for all routes back to the kernel.
>>   - Scan route's full nexthop list, ensuring all nexthop devs belong
>>     to the same switchdev device, otherwise don't try to install route
>>     to device.
>
> Getting really close.
>
> I think you have to make some minor adjustments to the
> fib_flush_external() cases.
>
> First of all, that code that unloads the entries from the hardware
> should clear the RTNH_F_EXTERNAL flag.

In v3, the setting and clearing of RTNH_F_EXTERNAL moved to the
driver, the implementer of the add/del ndo ops.  So RTNH_F_EXTERNAL
does get cleared by the driver on fib_flush_external().  We could add
an additional clear above the driver, just in case the driver screwed
up and forgot to clear it.  Driver bug in that case; not sure where to
draw the line.

> Secondly, if you call fib_flush_external() because an add returned an
> error, you have to set some boolean state which prevents the next new
> route insert from loading only that new route into the hardware
> because that's exactly what will happen with your current
> implementation.

I guess we could add a net.ipv4.fib_hw_screwed.  But that kills other
innocent switch devices on same netns.  Or is it a private driver
bool, which gets set on first install err, and is checked on
subsequent installs?
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