2012-12-21 11:45:20

by Chaitanya

Subject: [PATCH] mac80211: Fix the MAX MTU calculation

Fix the Max MTU calculations.
Do not take headers in to account, only MAX MSDU size
as per 802.11-2012(8.2.3) is enough.

ToDo: Add support for AMSDU in future.

Signed-off-by: T Krishna Chaitanya <[email protected]>
---

net/mac80211/iface.c | 23 ++++++++++++++++-------
1 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/net/mac80211/iface.c b/net/mac80211/iface.c
index 54fb7f9..5e5e876 100644
--- a/net/mac80211/iface.c
+++ b/net/mac80211/iface.c
@@ -207,15 +207,24 @@ void ieee80211_recalc_idle(struct ieee80211_local *local)

static int ieee80211_change_mtu(struct net_device *dev, int new_mtu)
{
- int meshhdrlen;
- struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
-
- meshhdrlen = (sdata->vif.type == NL80211_IFTYPE_MESH_POINT) ? 5 : 0;
+ /* 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 (skb_alloc) its handled properly.
+
+ ToDO: Make the MAX_DATA_LEN driver configurable through its
+ AMSDU capabilities.
+ */

- /* FIX: what would be proper limits for MTU?
- * This interface uses 802.3 frames. */
if (new_mtu < 256 ||
- new_mtu > IEEE80211_MAX_DATA_LEN - 24 - 6 - meshhdrlen) {
+ new_mtu > IEEE80211_MAX_DATA_LEN) {
return -EINVAL;
}

2012-12-21 14:11:05

by Johannes Berg

Subject: Re: [PATCH] mac80211: Fix the MAX MTU calculation

On Fri, 2012-12-21 at 17:15 +0530, Chaitanya wrote:
> Fix the Max MTU calculations.
> Do not take headers in to account, only MAX MSDU size
> as per 802.11-2012(8.2.3) is enough.

Applied, but I rewrote the changelog a bit,

> ToDo: Add support for AMSDU in future.

removed this (AMSDU is irrelevant here)

> - int meshhdrlen;
> - struct ieee80211_sub_if_data *sdata = IEEE80211_DEV_TO_SUB_IF(dev);
> -
> - meshhdrlen = (sdata->vif.type == NL80211_IFTYPE_MESH_POINT) ? 5 : 0;
> + /* 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 (skb_alloc) its handled properly.
> +
> + ToDO: Make the MAX_DATA_LEN driver configurable through its
> + AMSDU capabilities.
> + */

and I also removed the big comment that doesn't really apply

johannes