[XFRM]: Optimize MTU calculation
Replace the probing based MTU estimation, which usually takes 2-3 iterations
to find a fitting value and may underestimate the MTU, by an exact calculation.
Also fix underestimation of the XFRM trailer_len, which causes unnecessary
reallocations.
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/xfrm/xfrm_state.c b/net/xfrm/xfrm_state.c
index 63a20e8..69a3600 100644
--- a/net/xfrm/xfrm_state.c
+++ b/net/xfrm/xfrm_state.c
@@ -1667,37 +1667,17 @@
}
EXPORT_SYMBOL(xfrm_state_delete_tunnel);
-/*
- * This function is NOT optimal. For example, with ESP it will give an
- * MTU that's usually two bytes short of being optimal. However, it will
- * usually give an answer that's a multiple of 4 provided the input is
- * also a multiple of 4.
- */
int xfrm_state_mtu(struct xfrm_state *x, int mtu)
{
- int res = mtu;
+ int res;
- res -= x->props.header_len;
-
- for (;;) {
- int m = res;
-
- if (m < 68)
- return 68;
-
- spin_lock_bh(&x->lock);
- if (x->km.state == XFRM_STATE_VALID &&
- x->type && x->type->get_max_size)
- m = x->type->get_max_size(x, m);
- else
- m += x->props.header_len;
- spin_unlock_bh(&x->lock);
-
- if (m <= mtu)
- break;
- res -= (m - mtu);
- }
-
+ spin_lock_bh(&x->lock);
+ if (x->km.state == XFRM_STATE_VALID &&
+ x->type && x->type->get_mtu)
+ res = x->type->get_mtu(x, mtu);
+ else
+ res = mtu;
+ spin_unlock_bh(&x->lock);
return res;
}