[RFC net-next 1/2] ipv6: ioam: Support for Queue depth data field

[Justin Iurman <justin.iurman@uliege.be>]

This patch is an attempt to support the queue depth in IOAM trace data
fields. Any feedback is appreciated, or any other idea if this one is
not correct.

The draft [1] says the following:

   The "queue depth" field is a 4-octet unsigned integer field.  This
   field indicates the current length of the egress interface queue of
   the interface from where the packet is forwarded out.  The queue
   depth is expressed as the current amount of memory buffers used by
   the queue (a packet could consume one or more memory buffers,
   depending on its size).

An existing function (i.e., qdisc_qstats_qlen_backlog) is used to
retrieve the current queue length without reinventing the wheel. Any
comment on that?

Right now, the number of skb's (qlen) is returned, which is not totally
correct compared to what the draft says: "a packet could consume one or
more memory buffers". Any idea on a solution to take this into account?

Note: it was tested and qlen is increasing when an artificial delay is
added on the egress with tc.

  [1] https://datatracker.ietf.org/doc/html/draft-ietf-ippm-ioam-data#section-5.4.2.7

Signed-off-by: Justin Iurman <justin.iurman@uliege.be>
---
 net/ipv6/ioam6.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ioam6.c b/net/ipv6/ioam6.c
index 122a3d47424c..088eb2f877bc 100644
--- a/net/ipv6/ioam6.c
+++ b/net/ipv6/ioam6.c
@@ -13,10 +13,12 @@
 #include <linux/ioam6.h>
 #include <linux/ioam6_genl.h>
 #include <linux/rhashtable.h>
+#include <linux/netdevice.h>
 
 #include <net/addrconf.h>
 #include <net/genetlink.h>
 #include <net/ioam6.h>
+#include <net/sch_generic.h>
 
 static void ioam6_ns_release(struct ioam6_namespace *ns)
 {
@@ -717,7 +719,17 @@ static void __ioam6_fill_trace_data(struct sk_buff *skb,
 
 	/* queue depth */
 	if (trace->type.bit6) {
-		*(__be32 *)data = cpu_to_be32(IOAM6_U32_UNAVAILABLE);
+		struct netdev_queue *queue;
+		__u32 qlen, backlog;
+
+		if (skb_dst(skb)->dev->flags & IFF_LOOPBACK) {
+			*(__be32 *)data = cpu_to_be32(IOAM6_U32_UNAVAILABLE);
+		} else {
+			queue = skb_get_tx_queue(skb_dst(skb)->dev, skb);
+			qdisc_qstats_qlen_backlog(queue->qdisc, &qlen, &backlog);
+
+			*(__be32 *)data = cpu_to_be32(qlen);
+		}
 		data += sizeof(__be32);
 	}
 
-- 
2.25.1