netdev - Re: [PATCHv3 net-next-2.6 2/3] qlcnic: Take FW dump via ethtool

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Date:	Thu, 12 May 2011 22:02:47 +0100
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Anirban Chakraborty <anirban.chakraborty@...gic.com>
Cc:	netdev <netdev@...r.kernel.org>, David Miller <davem@...emloft.net>
Subject: Re: [PATCHv3 net-next-2.6 2/3] qlcnic: Take FW dump via ethtool

On Thu, 2011-05-12 at 13:54 -0700, Anirban Chakraborty wrote:
> On May 12, 2011, at 12:18 PM, Ben Hutchings wrote:
[...]
> > What prevents this sequence:
> > 
> > 1. Driver detects firmware dump is required, and creates the dump
> > (length L1).
> > 2. User changes firmware dump flags through ethtool.
> > 3. User starts to save firmware dump through ethtool:
> >   a. ethtool utility reads dump length (= L1) and allocates user buffer
> >   b. ethtool utility reads dump:
> >   c. ethtool core reads dump length (L1) and allocates kernel buffer
> > 4. Meanwhile, driver detects firmware dump is required again, and
> > creates a new dump (length L2, since dump flags changed)
> 
> This step won't happen as driver ensures that if a dump is taken that is not
> cleared yet by ethtool utility, it is not going to take any further dump. So, until
> the get_dump_data() has been called to fetch the dump data, changing dump
> flag (and hence dump size) will not have any effect.
> In 3 above, ethtool core created a buffer of L1 size but hasn't yet called 
> get_dump_data() of the driver, so driver is still holding onto its previously
> dumped data even though capture mask has been changed and the driver
> encountered a situation where it ought to take the dump.

OK, that sounds safe.

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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