dm-ioctl - info

We used to have a separate command to request basic information about a device, including whether or not it is suspended, whether it has Active and/or Inactive tables, whether it's read-only etc.
We found that this information was required so frequently that we decided it was better always to provide this information on return from commands dealing with single devices.
We always fill in all three of name, uuid and device-number.
We used to always fill in the reference count for the number of times the device is open, but this operation required a lock which was shown to affect multipath performance so it is now optional. Of course, to maintain backward compatibility userspace has to set a flag to say it doesn't want this field. Recent libdevmapper sets it most of the time.

We used to have a separate command to request basic information about a device, including whether or not it is suspended, whether it has Active and/or Inactive tables, whether it's read-only etc.