From 86878f14d71af89149a955122afd8b7af1ee9bf2 Mon Sep 17 00:00:00 2001 From: Jakub Kicinski Date: Mon, 5 Jun 2023 12:01:06 -0700 Subject: tools: ynl: user space helpers Add "fixed" part of the user space Netlink Spec-based library. This will get linked with the protocol implementations to form a full API. Acked-by: Willem de Bruijn Signed-off-by: Jakub Kicinski --- .../userspace-api/netlink/intro-specs.rst | 79 ++++++++++++++++++++++ 1 file changed, 79 insertions(+) (limited to 'Documentation/userspace-api/netlink') diff --git a/Documentation/userspace-api/netlink/intro-specs.rst b/Documentation/userspace-api/netlink/intro-specs.rst index a3b847eafff7..bada89699455 100644 --- a/Documentation/userspace-api/netlink/intro-specs.rst +++ b/Documentation/userspace-api/netlink/intro-specs.rst @@ -78,3 +78,82 @@ to see other examples. The code generation itself is performed by ``tools/net/ynl/ynl-gen-c.py`` but it takes a few arguments so calling it directly for each file quickly becomes tedious. + +YNL lib +======= + +``tools/net/ynl/lib/`` contains an implementation of a C library +(based on libmnl) which integrates with code generated by +``tools/net/ynl/ynl-gen-c.py`` to create easy to use netlink wrappers. + +YNL basics +---------- + +The YNL library consists of two parts - the generic code (functions +prefix by ``ynl_``) and per-family auto-generated code (prefixed +with the name of the family). + +To create a YNL socket call ynl_sock_create() passing the family +struct (family structs are exported by the auto-generated code). +ynl_sock_destroy() closes the socket. + +YNL requests +------------ + +Steps for issuing YNL requests are best explained on an example. +All the functions and types in this example come from the auto-generated +code (for the netdev family in this case): + +.. code-block:: c + + // 0. Request and response pointers + struct netdev_dev_get_req *req; + struct netdev_dev_get_rsp *d; + + // 1. Allocate a request + req = netdev_dev_get_req_alloc(); + // 2. Set request parameters (as needed) + netdev_dev_get_req_set_ifindex(req, ifindex); + + // 3. Issues the request + d = netdev_dev_get(ys, req); + // 4. Free the request arguments + netdev_dev_get_req_free(req); + // 5. Error check (the return value from step 3) + if (!d) { + // 6. Print the YNL-generated error + fprintf(stderr, "YNL: %s\n", ys->err.msg); + return -1; + } + + // ... do stuff with the response @d + + // 7. Free response + netdev_dev_get_rsp_free(d); + +YNL dumps +--------- + +Performing dumps follows similar pattern as requests. +Dumps return a list of objects terminated by a special marker, +or NULL on error. Use ``ynl_dump_foreach()`` to iterate over +the result. + +YNL notifications +----------------- + +YNL lib supports using the same socket for notifications and +requests. In case notifications arrive during processing of a request +they are queued internally and can be retrieved at a later time. + +To subscribed to notifications use ``ynl_subscribe()``. +The notifications have to be read out from the socket, +``ynl_socket_get_fd()`` returns the underlying socket fd which can +be plugged into appropriate asynchronous IO API like ``poll``, +or ``select``. + +Notifications can be retrieved using ``ynl_ntf_dequeue()`` and have +to be freed using ``ynl_ntf_free()``. Since we don't know the notification +type upfront the notifications are returned as ``struct ynl_ntf_base_type *`` +and user is expected to cast them to the appropriate full type based +on the ``cmd`` member. -- cgit