On 10/16/15 2:02 AM, Jiri Benc wrote:
On Fri, 16 Oct 2015 01:06:44 -0700 (PDT), David Miller wrote:
No, it's definitely not OK, because lwtunnel support exists in
Linus's tree.
And tools should be able to work on all kernels where lwtunnel support
is available.
You can consider the lwtunnels feature as not finished in the current
Linus's tree. It works, it won't change (thus anything using it in its
current form will continue to work in all the future kernels), but
mainstream tools won't make use of it until a kernel version later
which will get some additional support.
I don't think it's much of a problem and I don't think it is the first
time this would happen.
I'm afraid I don't have any solution that could do better.
What about a flag that requests the version from the relevant kernel
subsystem?
Generate the same initial netlink message -- e.g., type set to
RTM_NEWROUTE for example -- but with no attributes and the NLM_F_VERSION
flag set. Send the message using whatever socket protocol is relevant
for the command/query.
Then kernel side the message makes its way to the relevant handler, the
handler sees the flag asking for version and responds with its version.
The version would be local to the handler and is a means for telling
userspace what attributes it understands.
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