dm-ioctl - DM_SUSPEND

• Checks DM_SUSPEND_FLAG.

• If set, suspends a device by starting a queue to hold any future I/O sent to it.

• If there is already I/O in-flight to the device – i.e. sent to a lower level driver but not completed yet – it waits for it to be completed.

• If there is a filesystem directly using the device, it tells it to 'freeze' – make sure it is consistent on disk, so an fsck would not be necessary.

• If called without DM_SUSPEND_FLAG I/O, the opposite happens – resume. The filesystem is told to continue and queued I/O is released and sent on its way.

• Resume does one more crucial thing – if there is an Inactive table, it makes it Active, replacing an existing table.