Commit f1d0c998 authored by Committed by Steve FrenchBrowse files
Make CIFS mount work in a container.
Teach cifs about network namespaces, so mounting uses adresses/routing visible from the container rather than from init context. A container is a chroot on steroids that changes more than just the root filesystem the new processes see. One thing containers can isolate is "network namespaces", meaning each container can have its own set of ethernet interfaces, each with its own own IP address and routing to the outside world. And if you open a socket in _userspace_ from processes within such a container, this works fine. But sockets opened from within the kernel still use a single global networking context in a lot of places, meaning the new socket's address and routing are correct for PID 1 on the host, but are _not_ what userspace processes in the container get to use. So when you mount a network filesystem from within in a container, the mount code in the CIFS driver uses the host's networking context and not the container's networking context, so it gets the wrong address, uses the wrong routing, and may even try to go out an interface that the container can't even access... Bad stuff. This patch copies the mount process's network context into the CIFS structure that stores the rest of the server information for that mount point, and changes the socket open code to use the saved network context instead of the global network context. I.E. "when you attempt to use these addresses, do so relative to THIS set of network interfaces and routing rules, not the old global context from back before we supported containers". The big long HOWTO sets up a test environment on the assumption you've never used ocntainers before. It basically says: 1) configure and build a new kernel that has container support 2) build a new root filesystem that includes the userspace container control package (LXC) 3) package/run them under KVM (so you don't have to mess up your host system in order to play with containers). 4) set up some containers under the KVM system 5) set up contradictory routing in the KVM system and the container so that the host and the container see different things for the same address 6) try to mount a CIFS share from both contexts so you can both force it to work and force it to fail. For a long drawn out test reproduction sequence, see: http://landley.livejournal.com/47024.html http://landley.livejournal.com/47205.html http://landley.livejournal.com/47476.html Signed-off-by: Rob Landley <email@example.com> Reviewed-by: Jeff Layton <firstname.lastname@example.org> Signed-off-by: Steve French <email@example.com>
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