[PATCH net-next rfc 0/2] Allow unpriveledge user to disable tuntap queue

[Jason Wang <jasowang@redhat.com>]

This series is an rfc that tries to solve the issue that the queues of tuntap
could not be disabled/enabled by unpriveledged user. This is needed for
unpriveledge userspace such as qemu since guest may change the number of queues
at any time, qemu needs to configure the tuntap to disable/enable a specific
queue.

Instead of introducting new flag/ioctls, this series tries to re-use the current
TUNSETQUEUE and IFF_ATTACH_QUEUE/IFF_DETACH_QUEUE. After this change,
IFF_DETACH_QUEUE is used to disable a specific queue instead of detaching all
its state from tuntap. IFF_ATTACH_QUEUE is used to do: 1) creating new queue to
a tuntap device, in this situation, previous DAC check is still done. 2)
re-enable the queue previously disabled by IFF_DETACH_QUEUE, in this situation,
we can bypass some checking when we do during queue creating (the check need to
be done here needs discussion.

Management software (such as libvirt) then can do:
- TUNSETIFF to creating device and queue 0
- TUNSETQUEUE to create the rest of queues
- Passing them to unpriveledge userspace (such as qemu)

Then the unpriveledge userspace can enable and disable a specific queue through
IFF_ATTACH_QUEUE and IFF_DETACH_QUEUE.

This is done by introducing a enabled flags were used to notify whether the
queue is enabled, and tuntap only send/receive packets when it was enabled.

Please comment, thanks!

Jason Wang (2):
  tuntap: forbid calling TUNSETQUEUE for a persistent device with no
    queues
  tuntap: allow unpriveledge user to enable and disable queues

 drivers/net/tun.c |   78 +++++++++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 73 insertions(+), 5 deletions(-)