netdev - Re: [net-next PATCH v1 08/11] net: rocker: add get flow API operation

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Message-ID: <CAE4R7bCfpiCaiUwkOnPhHTRPJ3szcLtN8V8E35r=vKJ6rvTt3A@mail.gmail.com>
Date:	Mon, 5 Jan 2015 23:40:05 -0800
From:	Scott Feldman <sfeldma@...il.com>
To:	John Fastabend <john.fastabend@...il.com>
Cc:	Thomas Graf <tgraf@...g.ch>,
	Jiří Pírko <jiri@...nulli.us>,
	Jamal Hadi Salim <jhs@...atatu.com>,
	"simon.horman@...ronome.com" <simon.horman@...ronome.com>,
	Netdev <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [net-next PATCH v1 08/11] net: rocker: add get flow API operation

On Wed, Dec 31, 2014 at 11:48 AM, John Fastabend
<john.fastabend@...il.com> wrote:
> Add operations to get flows. I wouldn't mind cleaning this code
> up a bit but my first attempt to do this used macros which shortered
> the code up but when I was done I decided it just made the code
> unreadable and unmaintainable.
>
> I might think about it a bit more but this implementation albeit
> a bit long and repeatative is easier to understand IMO.

Dang, you put a lot of work into this one.

Something doesn't feel right though.  In this case, rocker driver just
happened to have cached all the flow/group stuff in hash tables in
software, so you don't need to query thru to the device to extract the
if_flow info.  What doesn't feel right is all the work need in the
driver.  For each and every driver.  get_flows needs to go above
driver, somehow.

Seems the caller of if_flow already knows the flows pushed down with
add_flows/del_flows, and with the err handling can't mess it up.

Is one use-case for get_flows to recover from a fatal OS/driver crash,
and to rely on hardware to recover flow set?  In this rocker example,
that's not going to work because driver didn't get thru to device to
get_flows.  I think I'd like to know more about the use-cases of
get_flows.

-scott
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