Re: [PATCH] Bluetooth: ISO: add socket option to report packet seqnum via CMSG

[Paul Menzel <pmenzel@molgen.mpg.de>]

Dear Pauli,


Thank you for your prompt reply.


Am 14.07.25 um 16:53 schrieb Pauli Virtanen:

> ma, 2025-07-14 kello 16:15 +0200, Paul Menzel kirjoitti:

>> Am 14.07.25 um 16:02 schrieb Pauli Virtanen:
>>> User applications need a way to track which ISO interval a given SDU
>>> belongs to, to properly detect packet loss. All controllers do not set
>>> timestamps, and it's not guaranteed user application receives all packet
>>> reports (small socket buffer, or controller doesn't send all reports
>>> like Intel AX210 is doing).
>>>
>>> Add socket option BT_PKT_SEQNUM that enables reporting of received
>>> packet ISO sequence number in BT_SCM_PKT_SEQNUM CMSG.
>>
>> Are there user applications already supporting this, so it can be tested?
> 
> I sent the associated tests to linux-bluetooth list
> 
> https://lore.kernel.org/linux-bluetooth/c9a75585e3640d8a1efca0bf96158eec1ca25fdc.1752501450.git.pav@iki.fi/

Awesome. Can this be referenced in the commit message?

>>> Signed-off-by: Pauli Virtanen <pav@iki.fi>
>>> ---
>>>
>>> Notes:
>>>       Intel AX210 is not sending all reports:
>>>       
>>>       $ btmon -r dump.btsnoop -I -C90|grep -A1 'ISO Data RX: Handle 2304'
>>>       ...
>>>       > ISO Data RX: Handle 2304 flags 0x02 dlen 64                      #1713 [hci0] 22.567744
>>>               dd 01 3c 00 6d 08 e9 14 1e 3b 85 7b 35 c2 25 0b  ..<.m....;.{5.%.
>>>       --
>>>       > ISO Data RX: Handle 2304 flags 0x02 dlen 64                      #1718 [hci0] 22.573745
>>>               de 01 3c 00 41 65 22 4f 99 9b 0b b6 ff cb 06 00  ..<.Ae"O........
>>>       --
>>>       > ISO Data RX: Handle 2304 flags 0x02 dlen 64                      #1727 [hci0] 22.587933
>>>               e0 01 3c 00 8b 6e 33 44 65 51 ee d7 e0 ee 49 d8  ..<..n3DeQ....I.
>>>       --
>>>       > ISO Data RX: Handle 2304 flags 0x02 dlen 64                      #1732 [hci0] 22.596742
>>>               e1 01 3c 00 a7 48 54 a7 c1 9f dc 37 66 fe 04 ab  ..<..HT....7f...
>>>       ...
>>>       
>>>       Here, report for packet with sequence number 0x01df is missing.
>>
>> Sorry, but where are the sequence number in the trace?
> 
> It's the first two bytes, see Core specification Vol 4E Sec 5.4.5 "HCI
> ISO Data packets".

Now I see it. Thank you!

>>>       
>>>       This may be spec violation by the controller, see Core v6.1 pp. 3702
>>>       
>>>           All SDUs shall be sent to the upper layer including the indication
>>>           of validity of data. A report shall be sent to the upper layer if
>>>           the SDU is completely missing.
>>>       
>>>       Regardless, it will be easier for user applications to see the HW
>>>       sequence numbers directly, so they don't have to count packets and it's
>>>       in any case more reliable if packets get dropped due to socket buffer
>>>       size.
>>
>> I wouldn’t mind to have the note in the commit message.
> 
> I'm not sure it's a spec violation --- the text in the specification is
> not fully clear what "All SDUs" means in the context here --- so I
> don't really want to say so in the commit message.
> 
> The limited socket buffer and that AX210 drops some reports is mentioned
> in the commit message.

True.

>>>    include/net/bluetooth/bluetooth.h |  9 ++++++++-
>>>    net/bluetooth/af_bluetooth.c      |  7 +++++++
>>>    net/bluetooth/iso.c               | 21 ++++++++++++++++++---
>>>    3 files changed, 33 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/include/net/bluetooth/bluetooth.h b/include/net/bluetooth/bluetooth.h
>>> index 114299bd8b98..0e31779a3341 100644
>>> --- a/include/net/bluetooth/bluetooth.h
>>> +++ b/include/net/bluetooth/bluetooth.h
>>> @@ -244,6 +244,10 @@ struct bt_codecs {
>>>    
>>>    #define BT_ISO_BASE		20
>>>    
>>> +#define BT_PKT_SEQNUM		21
>>> +
>>> +#define BT_SCM_PKT_SEQNUM	0x05
>>> +
>>>    __printf(1, 2)
>>>    void bt_info(const char *fmt, ...);
>>>    __printf(1, 2)
>>> @@ -391,7 +395,8 @@ struct bt_sock {
>>>    enum {
>>>    	BT_SK_DEFER_SETUP,
>>>    	BT_SK_SUSPEND,
>>> -	BT_SK_PKT_STATUS
>>> +	BT_SK_PKT_STATUS,
>>> +	BT_SK_PKT_SEQNUM,
>>>    };
>>>    
>>>    struct bt_sock_list {
>>> @@ -475,6 +480,7 @@ struct bt_skb_cb {
>>>    	u8 pkt_type;
>>>    	u8 force_active;
>>>    	u16 expect;
>>> +	u16 pkt_seqnum;
>>
>> Excuse my ignorance, just want to make sure, the type is big enough.
> 
> The hardware sequence number is also 16 bits.

Understood.

>>>    	u8 incoming:1;
>>>    	u8 pkt_status:2;
>>>    	union {
>>> @@ -488,6 +494,7 @@ struct bt_skb_cb {
>>>    
>>>    #define hci_skb_pkt_type(skb) bt_cb((skb))->pkt_type
>>>    #define hci_skb_pkt_status(skb) bt_cb((skb))->pkt_status
>>> +#define hci_skb_pkt_seqnum(skb) bt_cb((skb))->pkt_seqnum
>>>    #define hci_skb_expect(skb) bt_cb((skb))->expect
>>>    #define hci_skb_opcode(skb) bt_cb((skb))->hci.opcode
>>>    #define hci_skb_event(skb) bt_cb((skb))->hci.req_event
>>> diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
>>> index 6ad2f72f53f4..44b7acb20a67 100644
>>> --- a/net/bluetooth/af_bluetooth.c
>>> +++ b/net/bluetooth/af_bluetooth.c
>>> @@ -364,6 +364,13 @@ int bt_sock_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>>>    			put_cmsg(msg, SOL_BLUETOOTH, BT_SCM_PKT_STATUS,
>>>    				 sizeof(pkt_status), &pkt_status);
>>>    		}
>>> +
>>> +		if (test_bit(BT_SK_PKT_SEQNUM, &bt_sk(sk)->flags)) {
>>> +			u16 pkt_seqnum = hci_skb_pkt_seqnum(skb);
>>> +
>>> +			put_cmsg(msg, SOL_BLUETOOTH, BT_SCM_PKT_SEQNUM,
>>> +				 sizeof(pkt_seqnum), &pkt_seqnum);
>>> +		}
>>>    	}
>>>    
>>>    	skb_free_datagram(sk, skb);
>>> diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
>>> index fc22782cbeeb..469450bb6b6c 100644
>>> --- a/net/bluetooth/iso.c
>>> +++ b/net/bluetooth/iso.c
>>> @@ -1687,6 +1687,17 @@ static int iso_sock_setsockopt(struct socket *sock, int level, int optname,
>>>    			clear_bit(BT_SK_PKT_STATUS, &bt_sk(sk)->flags);
>>>    		break;
>>>    
>>> +	case BT_PKT_SEQNUM:
>>> +		err = copy_safe_from_sockptr(&opt, sizeof(opt), optval, optlen);
>>> +		if (err)
>>> +			break;
>>> +
>>> +		if (opt)
>>> +			set_bit(BT_SK_PKT_SEQNUM, &bt_sk(sk)->flags);
>>> +		else
>>> +			clear_bit(BT_SK_PKT_SEQNUM, &bt_sk(sk)->flags);
>>> +		break;
>>> +
>>>    	case BT_ISO_QOS:
>>>    		if (sk->sk_state != BT_OPEN && sk->sk_state != BT_BOUND &&
>>>    		    sk->sk_state != BT_CONNECT2 &&
>>> @@ -2278,7 +2289,7 @@ static void iso_disconn_cfm(struct hci_conn *hcon, __u8 reason)
>>>    void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
>>>    {
>>>    	struct iso_conn *conn = hcon->iso_data;
>>> -	__u16 pb, ts, len;
>>> +	__u16 pb, ts, len, sn;
>>
>> Use `seqnum` for consistency with the parts above.
>>
>>>    
>>>    	if (!conn)
>>>    		goto drop;
>>> @@ -2308,6 +2319,7 @@ void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
>>>    				goto drop;
>>>    			}
>>>    
>>> +			sn = hdr->sn;
>>>    			len = __le16_to_cpu(hdr->slen);
>>>    		} else {
>>>    			struct hci_iso_data_hdr *hdr;
>>> @@ -2318,18 +2330,20 @@ void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
>>>    				goto drop;
>>>    			}
>>>    
>>> +			sn = hdr->sn;
>>>    			len = __le16_to_cpu(hdr->slen);
>>>    		}
>>>    
>>>    		flags  = hci_iso_data_flags(len);
>>>    		len    = hci_iso_data_len(len);
>>>    
>>> -		BT_DBG("Start: total len %d, frag len %d flags 0x%4.4x", len,
>>> -		       skb->len, flags);
>>> +		BT_DBG("Start: total len %d, frag len %d flags 0x%4.4x sn %d",
>>> +		       len, skb->len, flags, sn);
>>>    
>>>    		if (len == skb->len) {
>>>    			/* Complete frame received */
>>>    			hci_skb_pkt_status(skb) = flags & 0x03;
>>> +			hci_skb_pkt_seqnum(skb) = sn;
>>>    			iso_recv_frame(conn, skb);
>>>    			return;
>>>    		}
>>> @@ -2352,6 +2366,7 @@ void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
>>>    			goto drop;
>>>    
>>>    		hci_skb_pkt_status(conn->rx_skb) = flags & 0x03;
>>> +		hci_skb_pkt_seqnum(conn->rx_skb) = sn;
>>>    		skb_copy_from_linear_data(skb, skb_put(conn->rx_skb, skb->len),
>>>    					  skb->len);
>>>    		conn->rx_len = len - skb->len;

Kind regards,

Paul