Proposal to send DM_UDEV_PRIMARY_SOURCE_FLAG w/ every ioctl sent in devicemapper-rs

[mulkieran]

The purpose of setting DM_UDEV_PRIMARY_SOURCE_FLAG is to distinguish a real from a synthetic udev event. When devicemapper code sends an ioctl that is, by definition, real, and associated events are also real. It is most appropriate for us always to set the DM_UDEV_PRIMARY_SOURCE_FLAG for every ioctl.

The programmatically simplest way to do this is to extend DmOptions::to_ioctl_hdr so that it always sets the DM_UDEV_PRIMARY_SOURCE_FLAG.

However, if we do this, certain udev rules that are now not run, because DM_UDEV_PRIMARY_SOURCE will be run when stratisd sets up its stack, and the devices will then be exposed.

To fix this, we need to make sure the correct cookies are sent when the devices are set up. To do this, we should generalize the commands that create devices so that they take a create_options parameter of type DmOptions and in stratisd, we must pass the correct arguments when creating devices. Note that this constitutes a breaking change for devicemapper-rs.

For stratisd's purposes, the flags DM_UDEV_DISABLE_DISK_RULES_FLAG, DM_UDEV_DISABLE_SUBSYSTEM_RULES_FLAG, DM_UDEV_DISABLE_OTHER_RULES_FLAG are probably the best ones to set.