[net-next,v2] net: psample: Introduce stubs to remove NIC driver dependency

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 <lkp@intel.com>
Signed-off-by: Chris Mi <cmi@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
---
v1->v2:
 - fix sparse errors

 include/net/psample.h    | 27 +++++++++++++++++++++++++++
 net/psample/psample.c    | 13 ++++++++++++-
 net/sched/Makefile       |  2 +-
 net/sched/psample_stub.c |  7 +++++++
 4 files changed, 47 insertions(+), 2 deletions(-)
 create mode 100644 net/sched/psample_stub.c

On Wed, Jan 27, 2021 at 5:06 PM Chris Mi <cmi@nvidia.com> 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 <lkp@intel.com>
> Signed-off-by: Chris Mi <cmi@nvidia.com>
> Reviewed-by: Jiri Pirko <jiri@nvidia.com>
> ---
> v1->v2:
>  - fix sparse errors
>
>  include/net/psample.h    | 27 +++++++++++++++++++++++++++
>  net/psample/psample.c    | 13 ++++++++++++-
>  net/sched/Makefile       |  2 +-
>  net/sched/psample_stub.c |  7 +++++++
>  4 files changed, 47 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..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>
>
>  struct psample_group {
>         struct list_head list;
> @@ -14,6 +15,15 @@ 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 +45,21 @@ static inline void psample_sample_packet(struct psample_group *group,
>
>  #endif
>
> +static inline void

inline is not needed here. The compiler should judge it.

Zhu Yanjun

> +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)
> +               psample_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..2a9fbfe09395 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 +461,17 @@ 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_INIT_POINTER(psample_ops, NULL);
>         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
>
>  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..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>
> +
> +const struct psample_ops __rcu *psample_ops __read_mostly;
> +EXPORT_SYMBOL_GPL(psample_ops);
> --
> 2.26.2
>