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

[Martin KaFai Lau <martin.lau@xxxxxxxxx>]

On 4/2/25 9:56 AM, Pauli Virtanen wrote:
> 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.

The idea was that the bpf prog can directly set the skb_shinfo(skb)->tskey if it 
is not used by the userspace. iirc, it is where the discussion left at during 
the earlier UDP support thread.


> 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.

The bpf_sock_ops_enable_tx_tstamp() has an used "u64 flags" argument. 
Potentially, it can use the higher 32bits to specify the 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);
> > > +
> > >    	}
> > >    }
> > >