netdev - Re: Why max netlink msg size is limited to 16k

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Date:   Wed, 24 May 2017 11:28:54 +0530
From:   prashantkumar dhotre <prashantkumardhotre@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: Why max netlink msg size is limited to 16k

Thanks
Can I use NLM_F_MULTI netlink multipart msg flag to send large buffer ?
I could not find example of that usage in sending case .

I have a kernel module and tryng to send large buffer to user app.
If I can use that flag, will kernel take care of splitting large
buffer into small chunks and will kernel also send NLMSG_DONE type msg
at end to user app?
How should I handle in user app.
Can you point me to few example please.

On Sat, Apr 22, 2017 at 9:06 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Sat, 2017-04-22 at 19:43 +0530, prashantkumar dhotre wrote:
>> I am observing that max netlink msg that my kernel module can send to
>> user app is close to 16K.
>>
>> For larger sizes, genlmsg_unicast() succeeds but my app does not receive data.
>>
>> I have tried increasing RECV buffer size in my user app but that does not help.
>>
>> Regards
>
>
> You need a kernel >= linux-4.9 to get about 32KB
>
> Why is this limited ? Please read
>
> https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git/commit/?id=d35c99ff77ecb2eb239731b799386f3b3637a31e
>
>
>