netdev - Re: [PATCH net-next v2 7/9] net: use core MTU range checking in misc drivers

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Message-ID: <20161022211606.3b5d137d@kant>
Date:   Sat, 22 Oct 2016 21:16:06 +0200
From:   Stefan Richter <stefanr@...6.in-berlin.de>
To:     Jarod Wilson <jarod@...hat.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        linux-rdma@...r.kernel.org, Faisal Latif <faisal.latif@...el.com>,
        Cliff Whickman <cpw@....com>,
        Robin Holt <robinmholt@...il.com>,
        Jes Sorensen <jes@...ined-monkey.org>,
        Marek Lindner <mareklindner@...mailbox.ch>,
        Simon Wunderlich <sw@...onwunderlich.de>,
        Antonio Quartulli <a@...table.cc>,
        Sathya Prakash <sathya.prakash@...adcom.com>,
        Chaitra P B <chaitra.basappa@...adcom.com>,
        Suganath Prabu Subramani 
        <suganath-prabu.subramani@...adcom.com>,
        MPT-FusionLinux.pdl@...adcom.com,
        Sebastian Reichel <sre@...nel.org>,
        Felipe Balbi <balbi@...nel.org>,
        Arvid Brodin <arvid.brodin@...en.se>,
        Remi Denis-Courmont <courmisch@...il.com>
Subject: Re: [PATCH net-next v2 7/9] net: use core MTU range checking in
 misc drivers

On Oct 20 Jarod Wilson wrote:
> firewire-net:
> - set min/max_mtu
> - remove fwnet_change_mtu
[...]
> --- a/drivers/firewire/net.c
> +++ b/drivers/firewire/net.c
[...]
> @@ -1478,9 +1467,10 @@ static int fwnet_probe(struct fw_unit *unit,
>  	 * Use the RFC 2734 default 1500 octets or the maximum payload
>  	 * as initial MTU
>  	 */
> -	max_mtu = (1 << (card->max_receive + 1))
> -		  - sizeof(struct rfc2734_header) - IEEE1394_GASP_HDR_SIZE;
> -	net->mtu = min(1500U, max_mtu);
> +	net->max_mtu = (1 << (card->max_receive + 1))
> +		       - sizeof(struct rfc2734_header) - IEEE1394_GASP_HDR_SIZE;
> +	net->mtu = min(1500U, net->max_mtu);
> +	net->min_mtu = ETH_MIN_MTU;
>  
>  	/* Set our hardware address while we're at it */
>  	ha = (union fwnet_hwaddr *)net->dev_addr;

Please preserve the current behavior, i.e. do not enforce any particular
upper bound.  (Especially none based on the local link layer controller's
max_receive parameter.)

BTW, after having read RFC 2734, RFC 3146, and the code, I am convinced
that net->mtu should be initialized to 1500, not less.  But such a change
should be done in a separate patch.
-- 
Stefan Richter
-======----- =-=- =-==-
http://arcgraph.de/sr/