netdev - Re: [PATCH 3/3] [RFC] Bluetooth: enable bpf TX timestamping

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Message-ID: <db7f317539cbda89df7e87efaea9b22328af610a.camel@iki.fi>
Date: Wed, 02 Apr 2025 19:56:52 +0300
From: Pauli Virtanen <pav@....fi>
To: Martin KaFai Lau <martin.lau@...ux.dev>
Cc: netdev@...r.kernel.org, bpf@...r.kernel.org, 
	linux-bluetooth@...r.kernel.org, willemdebruijn.kernel@...il.com, 
	kerneljasonxing@...il.com
Subject: Re: [PATCH 3/3] [RFC] Bluetooth: enable bpf TX timestamping

Hi,

ti, 2025-04-01 kello 18:34 -0700, Martin KaFai Lau kirjoitti:
> On 3/30/25 5:23 AM, Pauli Virtanen wrote:
> > Emit timestamps also for BPF timestamping.
> > 
> > ***
> > 
> > The tskey management here is not quite right: see cover letter.
> > ---
> >   include/net/bluetooth/bluetooth.h |  1 +
> >   net/bluetooth/hci_conn.c          | 21 +++++++++++++++++++--
> >   2 files changed, 20 insertions(+), 2 deletions(-)
> > 
> > diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
> > index bbefde319f95..3b2e59cedd2d 100644
> > --- a/include/net/bluetooth/bluetooth.h
> > +++ b/include/net/bluetooth/bluetooth.h
> > @@ -383,6 +383,7 @@ struct bt_sock {
> >   	struct list_head accept_q;
> >   	struct sock *parent;
> >   	unsigned long flags;
> > +	atomic_t bpf_tskey;
> >   	void (*skb_msg_name)(struct sk_buff *, void *, int *);
> >   	void (*skb_put_cmsg)(struct sk_buff *, struct msghdr *, struct sock *);
> >   };
> > diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
> > index 95972fd4c784..7430df1c5822 100644
> > --- a/net/bluetooth/hci_conn.c
> > +++ b/net/bluetooth/hci_conn.c
> > @@ -28,6 +28,7 @@
> >   #include <linux/export.h>
> >   #include <linux/debugfs.h>
> >   #include <linux/errqueue.h>
> > +#include <linux/bpf-cgroup.h>
> >   
> >   #include <net/bluetooth/bluetooth.h>
> >   #include <net/bluetooth/hci_core.h>
> > @@ -3072,6 +3073,7 @@ void hci_setup_tx_timestamp(struct sk_buff *skb, size_t key_offset,
> >   			    const struct sockcm_cookie *sockc)
> >   {
> >   	struct sock *sk = skb ? skb->sk : NULL;
> > +	bool have_tskey = false;
> >   
> >   	/* This shall be called on a single skb of those generated by user
> >   	 * sendmsg(), and only when the sendmsg() does not return error to
> > @@ -3096,6 +3098,20 @@ void hci_setup_tx_timestamp(struct sk_buff *skb, size_t key_offset,
> >   
> >   			skb_shinfo(skb)->tskey = key - 1;
> >   		}
> > +		have_tskey = true;
> > +	}
> > +
> > +	if (cgroup_bpf_enabled(CGROUP_SOCK_OPS) &&
> > +	    SK_BPF_CB_FLAG_TEST(sk, SK_BPF_CB_TX_TIMESTAMPING)) {
> > +		struct bt_sock *bt_sk = container_of(sk, struct bt_sock, sk);
> > +		int key = atomic_inc_return(&bt_sk->bpf_tskey);
> 
> I don't think it needs to add "atomic_t bpf_tskey". Allow the bpf to decide what 
> the skb_shinfo(skb)->tskey should be if it is not set by the userspace.

Ok. So if I understand correctly, the plan is that for UDP and
Bluetooth seqpacket sockets it works like this:

bpf_sock_ops_enable_tx_tstamp() does not set tskey.

Socket timestamping sets tskey the same way as previously.

So when both are in play, it shall work like:

* attach BPF timestamping
* setsockopt(SOF_TIMESTAMPING_SOFTWARE | SOF_TIMESTAMPING_OPT_ID)
* sendmsg() CMSG SO_TIMESTAMPING = 0
=> tskey 0 (unset)
* sendmsg() CMSG SO_TIMESTAMPING = SOF_TIMESTAMPING_TX_SOFTWARE
=> tskey 0
* sendmsg() CMSG SO_TIMESTAMPING = SOF_TIMESTAMPING_TX_SOFTWARE
=> tskey 1
* sendmsg() CMSG SO_TIMESTAMPING = 0
=> tskey 0 (unset)
* sendmsg() CMSG SO_TIMESTAMPING = 0
=> tskey 0 (unset)
* sendmsg() CMSG SO_TIMESTAMPING = 0
=> tskey 0 (unset)
* sendmsg() CMSG SO_TIMESTAMPING = SOF_TIMESTAMPING_TX_SOFTWARE
=> tskey 2

and BPF program has to handle the (unset) cases itself.

> 
> > +
> > +		if (!have_tskey)
> > +			skb_shinfo(skb)->tskey = key - 1;
> > +
> > +		bpf_skops_tx_timestamping(sk, skb,
> > +					  BPF_SOCK_OPS_TSTAMP_SENDMSG_CB);
> > +
> >   	}
> >   }
> >   
> 
> 

-- 
Pauli Virtanen