On Tue, Jun 16, 2015 at 07:42:31PM -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 only this
> call 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. This is the tricky part of it of this series.
>
> It smells hacky yes but currently most of sctp calls are wrapped behind
> kernel_*(). Even if we set a flag (like netlink does) saying that this
> is a kernel socket, we still have the issue of getting the function call
> through and returning such non-usual return value.
>
> I kept __user marker on sctp_getsockopt_peeloff_kernel() prototype and
> its helpers just to avoid issues with static checkers.
>
> Kernel path not really tested yet.. mainly willing to know what do you
> think, is this feasible? getsockopt option only reachable by kernel
> itself? Couldn't find any other like this.
>
> Thanks,
> Marcelo
>
> 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 | 39 +++++++++++++++++++++++++++++++++++++++
> 3 files changed, 59 insertions(+), 9 deletions(-)
>
> --
> 2.4.1
>
>
Why not just use the existing PEELOFF socket option with the kernel_getsockopt
interface, and sockfd_lookup to translate the returned value back to a socket
struct? That seems less redundant and less hack-ish to me.
Neil
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