Re: [RFC] mac80211: Fix MAX MTU Calculation

[Chaitanya <chaitanyatk@posedge.com>]

On Thursday 20 December 2012 06:37 PM, Johannes Berg wrote:
> On Thu, 2012-12-20 at 18:13 +0530, Chaitanya wrote:
>> Fix the MTU calculation, we should check for data_len+ mesh hdr len
>> and shouldn't include any header lengths.
>>
>> ToDo: Get the MAX_DATA_LEN based on driver's AMSDU capability.
>>
>> Signed-off-by: T Krishna Chaitanya <chaitanyatk@posedge.com>
>>
>> ---
>>
>>  net/mac80211/iface.c |   17 ++++++++++++++++-
>>  1 files changed, 16 insertions(+), 1 deletions(-)
>>
>> diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
>> index 54fb7f9..da74ef9 100644
>> --- a/net/mac80211/iface.c
>> +++ b/net/mac80211/iface.c
>> @@ -214,8 +214,23 @@ static int ieee80211_change_mtu(struct net_device *dev, int new_mtu)
>>  
>>  	/* FIX: what would be proper limits for MTU?
>>  	 * This interface uses 802.3 frames. */
>> +	/* Fixed: MTU needn't worry about headers*/
>> +
>> +	/* 802.11-2012: 8.2.3: The maximum frame body size is determined by
>> +	1. The maximum MSDU size (2304 octets),
>> +	2. plus the length of the Mesh Control field (6, 12, or 18 octets)
>> +		if present,
>> +	3. the maximum unencrypted MMPDU size excluding the MAC header and
>> +		FCS (2304 octets) or
>> +	4. the maximum A- MSDU size (3839 or 7935 octets),
>> +		plus any overhead from security encapsulation.
>> +	Note1: IEEE80211_MAX_DATA_LEN doesnt include any headers (2304),
>> +		so it can be used directly+ Mesh HDR Len
>> +	Note2: In Other places (like skb_alloc) its handled properly.
>> +	 */
>> +
> ok so the comment style is wrong, you shouldn't list changelog-type
> things in comments ("Fixed: ...") etc.
>
> I also don't understand why we should add the mesh length? It seems that
> this is really just the maximum MSDU size, i.e. 2304 octets.
>
> johannes
>
Ok, will change the comments.  So shall i remove the comments
for FIX as well (or) should i retain them?

As for WLAN is concerned the mesh
header is part of data (MSDU) hence the standard says the MSDU
can be Maximum of 2304 + Any Mesh Control Field. (#2 above).