Re: [PATCH net-next v5] net: psample: Introduce stubs to remove NIC driver dependency

[Chris Mi]

On 1/30/2021 10:52 PM, Ido Schimmel wrote:
On Sat, Jan 30, 2021 at 10:33:19AM +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>
This belongs in the changelog (that should be part of the commit
message). Something like "Fix xxx reported by kernel test robot".
But I see existing commits have it. And Jakub didn't ask me to do it. So 
I think
I'd better keep it.

Signed-off-by: Chris Mi <c...@nvidia.com>
Reviewed-by: Jiri Pirko <j...@nvidia.com>
---
v1->v2:
  - fix sparse errors
v2->v3:
  - remove inline
v3->v4:
  - add inline back
v4->v5:
  - address Jakub's comments

  include/net/psample.h    | 26 ++++++++++++++++++++++++++
  net/psample/psample.c    | 14 +++++++++++++-
  net/sched/Makefile       |  2 +-
  net/sched/psample_stub.c |  5 +++++
  4 files changed, 45 insertions(+), 2 deletions(-)
  create mode 100644 net/sched/psample_stub.c

diff --git a/include/net/psample.h b/include/net/psample.h
index 68ae16bb0a4a..d0f1cfc56f6f 100644
--- a/include/net/psample.h
+++ b/include/net/psample.h
@@ -14,6 +14,15 @@ struct psample_group {
        struct rcu_head rcu;
  };
  
+struct psample_ops {
+       void (*sample_packet)(struct psample_group *group, struct sk_buff *skb,
+                             u32 trunc_size, int in_ifindex, int out_ifindex,
+                             u32 sample_rate);
+
+};
+
+extern const struct psample_ops __rcu *psample_ops __read_mostly;
+
  struct psample_group *psample_group_get(struct net *net, u32 group_num);
  void psample_group_take(struct psample_group *group);
  void psample_group_put(struct psample_group *group);
@@ -35,4 +44,21 @@ static inline void psample_sample_packet(struct 
psample_group *group,
  
  #endif
  
+static inline void
+psample_nic_sample_packet(struct psample_group *group,
+                         struct sk_buff *skb, u32 trunc_size,
+                         int in_ifindex, int out_ifindex,
+                         u32 sample_rate)
+{
+       const struct psample_ops *ops;
+
+       rcu_read_lock();
+       ops = rcu_dereference(psample_ops);
+       if (ops)
+               ops->sample_packet(group, skb, trunc_size,
+                                  in_ifindex, out_ifindex,
+                                  sample_rate);
+       rcu_read_unlock();
+}
+
  #endif /* __NET_PSAMPLE_H */
diff --git a/net/psample/psample.c b/net/psample/psample.c
index 33e238c965bd..983ca5b698fe 100644
--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -8,6 +8,7 @@
  #include <linux/kernel.h>
  #include <linux/skbuff.h>
  #include <linux/module.h>
+#include <linux/rcupdate.h>
  #include <net/net_namespace.h>
  #include <net/sock.h>
  #include <net/netlink.h>
@@ -35,6 +36,10 @@ static const struct genl_multicast_group psample_nl_mcgrps[] 
= {
  
  static struct genl_family psample_nl_family __ro_after_init;
  
+static const struct psample_ops psample_sample_ops = {
+       .sample_packet  = psample_sample_packet,
+};
+
  static int psample_group_nl_fill(struct sk_buff *msg,
                                 struct psample_group *group,
                                 enum psample_command cmd, u32 portid, u32 seq,
@@ -456,11 +461,18 @@ EXPORT_SYMBOL_GPL(psample_sample_packet);
  
  static int __init psample_module_init(void)
  {
-       return genl_register_family(&psample_nl_family);
+       int ret;
+
+       ret = genl_register_family(&psample_nl_family);
+       if (!ret)
+               RCU_INIT_POINTER(psample_ops, &psample_sample_ops);
+       return ret;
  }
  
  static void __exit psample_module_exit(void)
  {
+       rcu_assign_pointer(psample_ops, NULL);
+       synchronize_rcu();
        genl_unregister_family(&psample_nl_family);
  }
  
diff --git a/net/sched/Makefile b/net/sched/Makefile
index dd14ef413fda..0d92bb98bb26 100644
--- a/net/sched/Makefile
+++ b/net/sched/Makefile
@@ -3,7 +3,7 @@
  # Makefile for the Linux Traffic Control Unit.
  #
  
-obj-y	:= sch_generic.o sch_mq.o
+obj-y  := sch_generic.o sch_mq.o psample_stub.o
Why the stub is under net/sched/ when psample is at net/psample/?
psample is not the same as 'act_sample'.
If this stub is in net/psample and compiled to psample kernel module, NIC
driver still depends on it. It must be in kernel. And I think net/sched 
is the
only place we can put. If we put it in somewhere else, like net/, I 
guess we'll
get more objections.

  
  obj-$(CONFIG_INET)		+= sch_frag.o
  obj-$(CONFIG_NET_SCHED)               += sch_api.o sch_blackhole.o
diff --git a/net/sched/psample_stub.c b/net/sched/psample_stub.c
new file mode 100644
index 000000000000..0541b8c5100d
--- /dev/null
+++ b/net/sched/psample_stub.c
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
psample has "// SPDX-License-Identifier: GPL-2.0-only"
Done. Thanks.

+/* Copyright (c) 2021 Mellanox Technologies. */
+
+const struct psample_ops __rcu *psample_ops __read_mostly;
+EXPORT_SYMBOL_GPL(psample_ops);
--
2.26.2