netdev - Re: [PATCH net-next] ipv6: ioam: Support for Queue depth data field

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Message-ID: <20211223192845.1586b5b2@kicinski-fedora-PC1C0HJN.hsd1.ca.comcast.net>
Date:   Thu, 23 Dec 2021 19:28:45 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Justin Iurman <justin.iurman@...ege.be>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, dsahern@...nel.org,
        yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH net-next] ipv6: ioam: Support for Queue depth data field

On Thu, 23 Dec 2021 16:55:15 +0100 Justin Iurman wrote:
> This patch adds support for the queue depth in IOAM trace data fields.
> 
> 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.
> 
> 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@...ege.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);
>  	}
>  

sparse complains that:

net/ipv6/ioam6.c:729:56: warning: incorrect type in argument 1 (different address spaces)
net/ipv6/ioam6.c:729:56:    expected struct Qdisc *sch
net/ipv6/ioam6.c:729:56:    got struct Qdisc [noderef] __rcu *qdisc