linux-kernel - Re: [PATCH 1/2] 8139too: Allow setting MTU larger than 1500

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Message-ID: <20141121145853.1be898de@tock>
Date:	Fri, 21 Nov 2014 14:58:53 +0100
From:	Alban <albeu@...e.fr>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Aban Bedel <albeu@...e.fr>, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
	Benoit Taine <benoit.taine@...6.fr>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 1/2] 8139too: Allow setting MTU larger than 1500

On Fri, 21 Nov 2014 00:34:34 +0000
Ben Hutchings <ben@...adent.org.uk> wrote:

> On Sat, 2014-11-08 at 12:48 +0100, Alban Bedel wrote:
> > Replace the default ndo_change_mtu callback with one that allow
> > setting MTU that the driver can handle.
> > 
> > Signed-off-by: Alban Bedel <albeu@...e.fr>
> > ---
> >  drivers/net/ethernet/realtek/8139too.c | 13 ++++++++++++-
> >  1 file changed, 12 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/realtek/8139too.c
> > b/drivers/net/ethernet/realtek/8139too.c index 007b38c..8387de9
> > 100644 --- a/drivers/net/ethernet/realtek/8139too.c
> > +++ b/drivers/net/ethernet/realtek/8139too.c
> > @@ -185,6 +185,9 @@ static int debug = -1;
> >  /* max supported ethernet frame size -- must be at least
> > (dev->mtu+14+4).*/ #define MAX_ETH_FRAME_SIZE	1536
> >  
> > +/* max supported payload size */
> > +#define MAX_ETH_DATA_SIZE	(MAX_ETH_FRAME_SIZE - ETH_HLEN -
> > ETH_FCS_LEN)
> [...]
> 
> Does this maximum still allow for VLAN tags, or should it use
> VLAN_ETH_HLEN instead of ETH_HLEN?

That might well be as the VLAN code seems to assume that the physical
device can handle frames of MTU + VLAN_HLEN bytes. I can fix it, but to
me it seems like the VLAN code should be fixed to respect the physical
device MTU.

Alban
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