On 17-06-2015 09:20, Neil Horman wrote:
On Wed, Jun 17, 2015 at 08:38:10AM -0300, Marcelo Ricardo Leitner wrote:
On 17-06-2015 07:21, Neil Horman wrote:
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.
It was like that before commit 2f2d76cc3e93 ("dlm: Do not allocate a fd for
peeloff"), but it caused serious issues due to the fd allocation, so that's
what I'm willing to avoid now.
References:
http://article.gmane.org/gmane.linux.network.drbd/22529
https://bugzilla.redhat.com/show_bug.cgi?id=1075629 (this one is closed,
sorry)
Marcelo
Ah, I see. You're using the new socket option as a differentiator to just skip
the creation of an FD.
Exactly.
I get your reasoning, but I'm still not in love with the idea of duplicating
code paths to avoid that action. Can we use some data inside the socket
structure to do this differentiation? Specifically here I'm thinking of
sock->file. IIRC that will be non-null for any sockets created in user space,
I had thought about using some socket flags like netlink does but
couldn't get around with that. Hadn't thought about sock->file though,
nice idea.
but will always be NULL for dlm created sockets (since we use sock_create
directly to create them. If that is a sufficient differentiator, then we can
just optionally allocate the new socket fd for the peeled off socket, iff the
parent sock->file pointer is non-null.
Thoughts?
Neil
We can re-use the current code path, by either checking it via
sock->file or via get_fs(). That will require us to change the option
arg format so we keep it nice and clean but as it would be kernel-side
only, it should be ok right? It currently is:
typedef struct {
sctp_assoc_t associd;
int sd;
} sctp_peeloff_arg_t;
And we would have to fit a pointer in there, something like:
typedef union {
struct {
sctp_assoc_t associd;
int sd;
};
void *sock;
} sctp_peeloff_arg_t;
Sounds good?
Marcelo
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