Re: [PATCH net-next v4] net: psample: Introduce stubs to remove NIC driver dependency

[Chris Mi]

On 1/30/2021 5:50 AM, Jakub Kicinski wrote:

On Thu, 28 Jan 2021 09:45:43 +0800 Chris Mi wrote:

In order to send sampled packets to userspace, NIC driver calls
psample api directly. But it creates a hard dependency on module
psample. Introduce psample_ops to remove the hard dependency.
It is initialized when psample module is loaded and set to NULL
when the module is unloaded.

Reported-by: kernel test robot <l...@intel.com>
Signed-off-by: Chris Mi <c...@nvidia.com>
Reviewed-by: Jiri Pirko <j...@nvidia.com>
diff --git a/include/net/psample.h b/include/net/psample.h
index 68ae16bb0a4a..e6a73128de59 100644
--- a/include/net/psample.h
+++ b/include/net/psample.h
@@ -4,6 +4,7 @@

#include <uapi/linux/psample.h>

  #include <linux/list.h>
+#include <linux/skbuff.h>

Forward declaration should be enough.

Done.

  struct psample_group {
        struct list_head list;
  static void __exit psample_module_exit(void)
  {
+       RCU_INIT_POINTER(psample_ops, NULL);

I think you can use rcu_assign_pointer(), it handles constants
right these days.

Done.

Please add a comment here saying that you depend on
genl_unregister_family() executing synchronize_rcu()
and name the function where it does so.

I added synchronize_rcu() here directly. Maybe it's more clear.

        genl_unregister_family(&psample_nl_family);
  }
diff --git a/net/sched/psample_stub.c b/net/sched/psample_stub.c
new file mode 100644
index 000000000000..0615a7b64000
--- /dev/null
+++ b/net/sched/psample_stub.c
@@ -0,0 +1,7 @@
+// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
+/* Copyright (c) 2021 Mellanox Technologies. */
+
+#include <net/psample.h>

Forward declaration is sufficient.

Done.

Thanks,
Chris

+const struct psample_ops __rcu *psample_ops __read_mostly;
+EXPORT_SYMBOL_GPL(psample_ops);