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Message-ID: <20131216143223.GB19809@hmsreliant.think-freely.org>
Date: Mon, 16 Dec 2013 09:32:23 -0500
From: Neil Horman <nhorman@...driver.com>
To: Wang Weidong <weidong1991.wang@...il.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
On Mon, Dec 16, 2013 at 10:14:55PM +0800, Wang Weidong wrote:
> 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.
>
Ah thats right, I remember doing this before now. My bad.
> >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?
>
It really seems like there should be a way to roll up what you want into the
try_then_request_module macro. What about:
ret = try_then_request_module((register_jprobe(...) == 0), "sctp");
That seems like it should work. It will mask the actual return value of
register_jprobe though I think, which kind of sucks. Its almost like we need
another variant of this macro that accepts an expected condition result so the
macro can use it to compare, something like:
#define try_then_request_module_cond(x, result, mod...) \
((x) == (result) ?: __request_module(true, mod), (x)))
that would let you set an expected comparison value for your macro, but get the
result of the method if it still fails after the module is loaded, or if it
fails to load.
Thats probably a cleanup for a second patch. I think your version two is
probably as close as we're going to get right now. So for v2:
Acked-by: Neil Horman <nhorman@...driver.com>
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