Commit aee6479a authored by Jeremy Kerr's avatar Jeremy Kerr Committed by Paolo Abeni
Browse files

net: mctp: Add some detail on the key allocation implementation 



We could do with a little more comment on where MCTP_ADDR_ANY will match
in the key allocations.

Signed-off-by: default avatarJeremy Kerr <jk@codeconstruct.com.au>
Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent ee076b73

net/mctp/route.c

+37 −0
Original line number Diff line number Diff line
@@ -73,6 +73,40 @@ static struct mctp_sock *mctp_lookup_bind(struct net *net, struct sk_buff *skb) 
	return NULL;

}



/* A note on the key allocations.

 *

 * struct net->mctp.keys contains our set of currently-allocated keys for

 * MCTP tag management. The lookup tuple for these is the peer EID,

 * local EID and MCTP tag.

 *

 * In some cases, the peer EID may be MCTP_EID_ANY: for example, when a

 * broadcast message is sent, we may receive responses from any peer EID.

 * Because the broadcast dest address is equivalent to ANY, we create

 * a key with (local = local-eid, peer = ANY). This allows a match on the

 * incoming broadcast responses from any peer.

 *

 * We perform lookups when packets are received, and when tags are allocated

 * in two scenarios:

 *

 *  - when a packet is sent, with a locally-owned tag: we need to find an

 *    unused tag value for the (local, peer) EID pair.

 *

 *  - when a tag is manually allocated: we need to find an unused tag value

 *    for the peer EID, but don't have a specific local EID at that stage.

 *

 * in the latter case, on successful allocation, we end up with a tag with

 * (local = ANY, peer = peer-eid).

 *

 * So, the key set allows both a local EID of ANY, as well as a peer EID of

 * ANY in the lookup tuple. Both may be ANY if we prealloc for a broadcast.

 * The matching (in mctp_key_match()) during lookup allows the match value to

 * be ANY in either the dest or source addresses.

 *

 * When allocating (+ inserting) a tag, we need to check for conflicts amongst

 * the existing tag set. This requires macthing either exactly on the local

 * and peer addresses, or either being ANY.

 */



static bool mctp_key_match(struct mctp_sk_key *key, mctp_eid_t local,

			   mctp_eid_t peer, u8 tag)

{
@@ -368,6 +402,9 @@ static int mctp_route_input(struct mctp_route *route, struct sk_buff *skb) 
			 * key lookup to find the socket, but don't use this

			 * key for reassembly - we'll create a more specific

			 * one for future packets if required (ie, !EOM).

			 *

			 * this lookup requires key->peer to be MCTP_ADDR_ANY,

			 * it doesn't match just any key->peer.

			 */

			any_key = mctp_lookup_key(net, skb, MCTP_ADDR_ANY, &f);

			if (any_key) {