fuse scalability part 1

[Miklos Szeredi <miklos@szeredi.hu>]

This part splits out an "input queue" and a "processing queue" from the
monolithic "fuse connection", each of those having their own spinlock.

The end of the patchset adds the ability to "clone" a fuse connection.  This
means, that instead of having to read/write requests/answers on a single fuse
device fd, the fuse daemon can have multiple distinct file descriptors open.
Each of those can be used to receive requests and send answers, currently the
only constraint is that a request must be answered on the same fd as it was read
from.

This can be extended further to allow binding a device clone to a specific CPU
or NUMA node.

Patchset is available here:

  git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/fuse.git for-next

Libfuse patches adding support for "clone_fd" option:

  git://git.code.sf.net/p/fuse/fuse clone_fd

Thanks,
Miklos