netdev - Re: [PATCH v2] sctp: loading sctp when load sctp

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Date:	Mon, 16 Dec 2013 22:14:55 +0800
From:	Wang Weidong <weidong1991.wang@...il.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	Vlad Yasevich <vyasevich@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH v2] sctp: loading sctp when load sctp_probe

From: Wang Weidong <wangweidong1@...wei.com>

On 2013/12/16 21:48, Neil Horman wrote:
> On Mon, Dec 16, 2013 at 10:47:00AM +0800, Wang Weidong wrote:
>> On 2013/12/13 20:26, Neil Horman wrote:
>>> On Fri, Dec 13, 2013 at 11:00:10AM +0800, Wang Weidong wrote:
>>>> when I modprobe sctp_probe, it failed with "FATAL: ". I found that
>>>> sctp should load before sctp_probe register jprobe. So I add a
>>>> sctp_setup_jprobe for loading 'sctp' when first failed to register
>>>> jprobe, just do this similar to dccp_probe.
>>>>
>>>> v2: add MODULE_SOFTDEP and check of request_module, as suggested by Neil
>>>>
>>>> Signed-off-by: Wang Weidong <wangweidong1@...wei.com>
>>>> ---
>>>>   net/sctp/probe.c | 17 ++++++++++++++++-
>>>>   1 file changed, 16 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/net/sctp/probe.c b/net/sctp/probe.c
>>>> index 53c452e..5e68b94 100644
>>>> --- a/net/sctp/probe.c
>>>> +++ b/net/sctp/probe.c
>>>> @@ -38,6 +38,7 @@
>>>>   #include <net/sctp/sctp.h>
>>>>   #include <net/sctp/sm.h>
>>>>
>>>> +MODULE_SOFTDEP("pre: sctp");
>>>>   MODULE_AUTHOR("Wei Yongjun <yjwei@...fujitsu.com>");
>>>>   MODULE_DESCRIPTION("SCTP snooper");
>>>>   MODULE_LICENSE("GPL");
>>>> @@ -182,6 +183,20 @@ static struct jprobe sctp_recv_probe = {
>>>>   	.entry	= jsctp_sf_eat_sack,
>>>>   };
>>>>
>>>> +static __init int sctp_setup_jprobe(void)
>>>> +{
>>>> +	int ret = register_jprobe(&sctp_recv_probe);
>>>> +
>>>> +	if (ret) {
>>>> +		if (request_module("sctp"))
>>>> +			goto out;
>>>> +		ret = register_jprobe(&sctp_recv_probe);
>>>> +	}
>>>> +
>>>> +out:
>>>> +	return ret;
>>>> +}
>>>> +
>>>>   static __init int sctpprobe_init(void)
>>>>   {
>>>>   	int ret = -ENOMEM;
>>>> @@ -202,7 +217,7 @@ static __init int sctpprobe_init(void)
>>>>   			 &sctpprobe_fops))
>>>>   		goto free_kfifo;
>>>>
>>>> -	ret = register_jprobe(&sctp_recv_probe);
>>>> +	ret = sctp_setup_jprobe();
>>> You don't need to create your own function for this, you can collapse it down to
>>> a call to try_then_request_module(regitser_jprobe(...), "sctp");
>>> Neil
>>>
>> Hi Neil,
>>
>> I try to use try_then_request_module(!regitser_jprobe(...), "sctp"); I found that if
>> I used this, I couldn't get the ture value which returned by register_jprobe(). Is the
>> returned value not important? The problem("if sctp.ko doesn't exist") you had pointed out
>> is exist as well.
>>
>> Regards.
>> Wang
>
> Not sure I follow.  There appear to be lots of examples in the kernel where

I do this just like the dccp/probe.c do. So I think it can be an example.

> exactly what you are trying to do is done.  try_then_request_module calls your
> requested method, and if it returns non-zero, calls request_module, then calls

No actually. Just look the definition:
#define try_then_request_module(x, mod...) \
          ((x) ?: (__request_module(true, mod), (x)))
if x return non-zero, it will return the value, not call request_module.

> your requested method again, returning the final result.  What problem are you
> running into?
> Neil
>

So I only can use it like this:
try_then_request_module(!regitser_jprobe(...), "sctp");

when register_jprobe return 0 indicates success, I get the value is 1. It is OK.

when register_jprobe is non-zero indicates failed, then calls request_module,
and last calls register_jprobe. Here,
1)maybe it will failed return non-zero, what I get the value is !register_jprobe
is 0 with losing the value.
2)request_module failed with the sctp is not exist, it will do the register_jprobe
as well.

Is there I am wrong somewhere?

Regards.
Wang

>>>
>>>>   	if (ret)
>>>>   		goto remove_proc;
>>>>
>>>
>>> .
>>>
>>
>>
>>
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