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docs: net: update devmem code examples

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Update the code examples
 - update the YNL sample with the latest(?) APIs
 - struct dmabuf_tx_cmsg does not exist, use __u32 directly

Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20260526160151.2793354-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski
2026-05-26 09:01:45 -07:00
parent 73ac86c584
commit 427837e5fd
1 changed files with 11 additions and 16 deletions
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27
Documentation/networking/devmem.rst
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@@ -103,24 +103,22 @@ The user must bind a dmabuf to any number of RX queues on a given NIC using
the netlink API::
/* Bind dmabuf to NIC RX queue 15 */
struct netdev_queue *queues;
queues = malloc(sizeof(*queues) * 1);
struct netdev_queue_id *queues;
queues[0]._present.type = 1;
queues[0]._present.idx = 1;
queues[0].type = NETDEV_RX_QUEUE_TYPE_RX;
queues[0].idx = 15;
queues = netdev_queue_id_alloc(1);
netdev_queue_id_set_type(&queues[0], NETDEV_QUEUE_TYPE_RX);
netdev_queue_id_set_id(&queues[0], 15);
*ys = ynl_sock_create(&ynl_netdev_family, &yerr);
req = netdev_bind_rx_req_alloc();
netdev_bind_rx_req_set_ifindex(req, 1 /* ifindex */);
netdev_bind_rx_req_set_dmabuf_fd(req, dmabuf_fd);
__netdev_bind_rx_req_set_queues(req, queues, n_queue_index);
netdev_bind_rx_req_set_fd(req, dmabuf_fd);
__netdev_bind_rx_req_set_queues(req, queues, 1);
rsp = netdev_bind_rx(*ys, req);
dmabuf_id = rsp->dmabuf_id;
dmabuf_id = rsp->id;
The netlink API returns a dmabuf_id: a unique ID that refers to this dmabuf
@@ -302,13 +300,12 @@ The user should create a msghdr where,
* iov_base is set to the offset into the dmabuf to start sending from
* iov_len is set to the number of bytes to be sent from the dmabuf
The user passes the dma-buf id to send from via the dmabuf_tx_cmsg.dmabuf_id.
The user passes the dma-buf id to send from as a u32 cmsg payload.
The example below sends 1024 bytes from offset 100 into the dmabuf, and 2048
from offset 2000 into the dmabuf. The dmabuf to send from is tx_dmabuf_id::
char ctrl_data[CMSG_SPACE(sizeof(struct dmabuf_tx_cmsg))];
struct dmabuf_tx_cmsg ddmabuf;
char ctrl_data[CMSG_SPACE(sizeof(__u32))];
struct msghdr msg = {};
struct cmsghdr *cmsg;
struct iovec iov[2];
@@ -327,11 +324,9 @@ from offset 2000 into the dmabuf. The dmabuf to send from is tx_dmabuf_id::
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_DEVMEM_DMABUF;
cmsg->cmsg_len = CMSG_LEN(sizeof(struct dmabuf_tx_cmsg));
cmsg->cmsg_len = CMSG_LEN(sizeof(__u32));
ddmabuf.dmabuf_id = tx_dmabuf_id;
*((struct dmabuf_tx_cmsg *)CMSG_DATA(cmsg)) = ddmabuf;
*((__u32 *)CMSG_DATA(cmsg)) = tx_dmabuf_id;
sendmsg(socket_fd, &msg, MSG_ZEROCOPY);