Re: [PATCH v2] Bluetooth: ISO: Support SOCK_RCVTSTAMP via CMSG for ISO sockets

From: Yang Li
Date: Wed Jul 02 2025 - 08:28:07 EST

Hi Paul,
[ EXTERNAL EMAIL ]

Dear Li,


Thank you for your patch.


Am 02.07.25 um 13:35 schrieb Yang Li via B4 Relay:
From: Yang Li <yang.li@xxxxxxxxxxx>

User-space applications (e.g., PipeWire) depend on
ISO-formatted timestamps for precise audio sync.

Does PipeWire log anything? It’d be great if you could add how to
reproduce the issue including the PipeWire version.


Pipewire version: 1.2.7

I have modified the patch as follows:

diff --git a/spa/plugins/bluez5/media-source.c b/spa/plugins/bluez5/media-source.c
index 488cf49..2fe08b8 100644
--- a/spa/plugins/bluez5/media-source.c
+++ b/spa/plugins/bluez5/media-source.c
@@ -404,9 +404,22 @@ static int32_t read_data(struct impl *this) {
     const ssize_t b_size = sizeof(this->buffer_read);
     int32_t size_read = 0;

+    struct msghdr msg = {0};
+    struct iovec iov;
+    char control[128];
+    struct timespec *ts = NULL;
+
+    iov.iov_base = this->buffer_read;
+    iov.iov_len = b_size;
+
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+    msg.msg_control = control;
+    msg.msg_controllen = sizeof(control);
+
 again:
-    /* read data from socket */
-    size_read = recv(this->fd, this->buffer_read, b_size, MSG_DONTWAIT);
+    /* read data from socket, with timestamp */
+    size_read = recvmsg(this->fd, &msg, MSG_DONTWAIT);

     if (size_read == 0)
         return 0;
@@ -417,13 +430,26 @@ again:

         /* return socket has no data */
         if (errno == EAGAIN || errno == EWOULDBLOCK)
-            return 0;
+            return 0;

         /* go to 'stop' if socket has an error */
         spa_log_error(this->log, "read error: %s", strerror(errno));
         return -errno;
     }

+    struct cmsghdr *cmsg;
+    for (cmsg = CMSG_FIRSTHDR(&msg); cmsg != NULL; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+#ifdef SO_TIMESTAMPNS
+        /* Check for timestamp */
+        if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SO_TIMESTAMPNS) {
+            ts = (struct timespec *)CMSG_DATA(cmsg);
+            spa_log_trace(this->log, "%p: received timestamp %ld.%09ld",
+                    this, (long)ts->tv_sec, (long)ts->tv_nsec);
+            break;
+        }
+#endif
+    }
+
     return size_read;
 }

@@ -700,6 +726,12 @@ static int transport_start(struct impl *this)
     if (setsockopt(this->fd, SOL_SOCKET, SO_PRIORITY, &val, sizeof(val)) < 0)
         spa_log_warn(this->log, "SO_PRIORITY failed: %m");

+    val = 1;
+    if (setsockopt(this->fd, SOL_SOCKET, SO_TIMESTAMPNS, &val, sizeof(val)) < 0) {
+        spa_log_warn(this->log, "SO_TIMESTAMPNS failed: %m");
+        /* don't fail if timestamping is not supported */
+    }
+
     reset_buffers(port);

     spa_bt_decode_buffer_clear(&port->buffer);


Pipewire log as below:

03:40:00.850312 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017361972
03:40:00.850571 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017361972
03:40:00.860241 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017371972
03:40:00.860430 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017371972
03:40:00.870166 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017381972
03:40:00.870343 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017381972
03:40:00.880197 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017391972
03:40:00.880370 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017391972
03:40:00.890405 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017401972
03:40:00.890642 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017401972
03:40:00.900201 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017411972
03:40:00.900652 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017411972
03:40:00.910391 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017421972
03:40:00.910694 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017421972
03:40:00.920198 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017431972
03:40:00.920352 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017431972
03:40:00.930438 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017441972
03:40:00.930699 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017441972
03:40:00.940171 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017451972
03:40:00.940331 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017451972
03:40:00.950427 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017461972
03:40:00.950678 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017461972
03:40:00.960447 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017471972
03:40:00.960703 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017471972
03:40:00.970154 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017481972
03:40:00.970308 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017481972
03:40:00.980443 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017491972
03:40:00.980667 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017491972
03:40:00.990455 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017501972
03:40:00.990706 spa.bluez5.source. ../spa/plugins/bluez5/media-source.c:450:read_data: received timestamp: 0.017501972


Signed-off-by: Yang Li <yang.li@xxxxxxxxxxx>
---
Changes in v2:
- Support SOCK_RCVTSTAMPNS via CMSG for ISO sockets
- Link to v1: https://lore.kernel.org/r/20250429-iso_ts-v1-1-e586f30de6cb@xxxxxxxxxxx
---
  net/bluetooth/iso.c | 3 +++
  1 file changed, 3 insertions(+)

diff --git a/net/bluetooth/iso.c b/net/bluetooth/iso.c
index fc22782cbeeb..6927c593a1d6 100644
--- a/net/bluetooth/iso.c
+++ b/net/bluetooth/iso.c
@@ -2308,6 +2308,9 @@ void iso_recv(struct hci_conn *hcon, struct sk_buff *skb, u16 flags)
                              goto drop;
                      }

+                     /* Record the timestamp to skb*/
+                     skb->skb_mstamp_ns = le32_to_cpu(hdr->ts);
+
                      len = __le16_to_cpu(hdr->slen);
              } else {
                      struct hci_iso_data_hdr *hdr;

Kind regards,

Paul