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

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Date:   Sat, 30 Jan 2021 10:35:10 +0800
From:   Chris Mi <cmi@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     <netdev@...r.kernel.org>, <jiri@...dia.com>, <saeedm@...dia.com>,
        "kernel test robot" <lkp@...el.com>
Subject: Re: [PATCH net-next v4] net: psample: Introduce stubs to remove NIC
 driver dependency

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 <lkp@...el.com>
>> Signed-off-by: Chris Mi <cmi@...dia.com>
>> Reviewed-by: Jiri Pirko <jiri@...dia.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);