netdev - Re: [PATCH 7/7] bnx2x: expose HW RX VLAN stripping toggle

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Message-ID: <4E5D3A43.1060202@redhat.com>
Date:	Tue, 30 Aug 2011 21:30:11 +0200
From:	Michal Schmidt <mschmidt@...hat.com>
To:	Michał Mirosław <mirqus@...il.com>
CC:	netdev@...r.kernel.org, vladz@...adcom.com, dmitry@...adcom.com,
	eilong@...adcom.com
Subject: Re: [PATCH 7/7] bnx2x: expose HW RX VLAN stripping toggle

On 08/30/2011 08:27 PM, Michał Mirosław wrote:
> It seems rather convoluted and unnecessary that you mirror
> NETIF_F_HW_VLAN_RX in bp->flags

This mirroring is for the benefit of functions called indirectly from 
bnx2x_set_features(). They cannot look at dev->features for 
NETIF_F_HW_VLAN_RX because it's not set before ->ndo_set_features() returns.

> and then also in fp->flags.  Are the
> fp->flags strictly mirroring hardware state (as in: there is no way
> the states can differ in any point in time where the flags are
> tested)?

Yes. This is the purpose of the second mirroring of the flag.

> For this to be true, the two functions above need to be
> called only without releasing a lock between them that is also taken
> by receive handler.

The flag propagates from bp->flags to fp->flags between unloading and 
reloading the NIC. The receive handler cannot run at the time.

> Isn't there a flag in the rx descriptor of a
> packet that says if VLAN was stripped? (All that flag keeping would be
> unnecessary then.)

There is no such flag, AFAIK.

Michal
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