netdev - Re: [PATCH v2 0/2] Avoid link dependency of dlm on sctp module

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Date:	Wed, 15 Jul 2015 09:57:14 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
Cc:	netdev@...r.kernel.org, Vlad Yasevich <vyasevich@...il.com>,
	linux-sctp@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Avoid link dependency of dlm on sctp module

On Tue, Jul 14, 2015 at 02:13:23PM -0300, Marcelo Ricardo Leitner wrote:
> Hi,
> 
> I'm trying to remove a direct dependency of dlm module on sctp one.
> Currently dlm code is calling sctp_do_peeloff() directly and this call
> only is causing the load of sctp module together with dlm. For that, we
> have basically 3 options:
> - Doing a module split on dlm
>   - which I'm avoiding because it was already split and was merged (more
>     info on patch2 changelog)
>   - and the sctp code on it is rather small if compared with sctp module
>     itself
> - Using some other infra that gets indirectly activated, like getsockopt()
>   - It was like this before, but the exposed sockopt created a file
>     descriptor for the new socket and that create some serious issues.
>     More info on 2f2d76cc3e93 ("dlm: Do not allocate a fd for peeloff")
> - Doing something like ipv6_stub (which is used by vxlan) or similar
>   - but I don't feel that's a good way out here, it doesn't feel right.
> 
> So I'm approaching this by going with 2nd option again but this time
> also creating a new sockopt that is only accessible for kernel users of
> this protocol, so that we are safe to directly return a struct socket *
> via getsockopt() results.
> 
> "Kernel users" are identified by sockets that don't have a file
> descriptor attached to it, as only kernel users are allowed to do that
> and, if original socket has a file descriptor, one should just use the
> original option.
> 
> I kept __user marker on sctp_getsockopt_peeloff_kernel() prototype and
> its helpers just to avoid issues with static checkers.
> 
> I tried minimizing the code duplication while adding the new option, but
> it's just better to add a whole new function to handle it. As the
> sockopt arguments are different, the only thing in common between both
> call handlers is the call to sctp_do_peeloff(). All rest would have to
> have checks around it.
> 
> RFC->v1, from Neil:
>  - For identifying kernel users, switched from segment_eq() to fd check
>  - Reused original option to avoid code duplication
> v1->v2, from David:
>  - Back to new sockopt implementation, to avoid changing sockopt arg
>    format.
> 
> 
> Marcelo Ricardo Leitner (2):
>   sctp: add new getsockopt option SCTP_SOCKOPT_PEELOFF_KERNEL
>   dlm: avoid using sctp_do_peeloff directly
> 
>  fs/dlm/lowcomms.c         | 17 ++++++++---------
>  include/uapi/linux/sctp.h | 12 ++++++++++++
>  net/sctp/socket.c         | 37 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 57 insertions(+), 9 deletions(-)
> 
> -- 
> 2.4.1
> 
> --
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> 

Series
Acked-by: Neil Horman <nhorman@...driver.com>

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