tree 33ef078dc10f73ad9eff20777fdcbad88742a6c1
parent 93e6442c76a0d26ad028c5df9b4a1e3096d9c36b
author Mikulas Patocka <mpatocka@redhat.com> 1494007972 -0700
committer Mike Snitzer <snitzer@redhat.com> 1497884629 -0400

dm ioctl: add a new DM_DEV_ARM_POLL ioctl

This ioctl will record the current global event number in the structure
dm_file, so that next select or poll call will wait until new events
arrived since this ioctl.

The DM_DEV_ARM_POLL ioctl has the same effect as closing and reopening
the handle.

Using the DM_DEV_ARM_POLL ioctl is optional - if the userspace is OK
with closing and reopening the /dev/mapper/control handle after select
or poll, there is no need to re-arm via ioctl.

Usage:
1. open the /dev/mapper/control device
2. send the DM_DEV_ARM_POLL ioctl
3. scan the event numbers of all devices we are interested in and process
   them
4. call select, poll or epoll on the handle (it waits until some new event
   happens since the DM_DEV_ARM_POLL ioctl)
5. go to step 2

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Andy Grover <agrover@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>