Create UCI fstab mount sections for existing volumes on firstboot.
Introduce special handling for volumes with non-[:alnum:] prefix:
 - do not create UCI sections for these 'hidden' volumes
 - create UCI section for '.uxc' special volume with target
   /var/state/uxc to be used for uxc config.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

* genrate UCI fstab configs for each volume before first 'up'
 * remove UCI section on volume remove
 * use autofs automounter for read-only volumes
 * try umount on 'down'
 * emulate hotplug events for UBI volume up/down
 * more robust error paths

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

Emmit ubus events when volumes come up/down.
Make sure volume state is always well defined by introducing
additional state 'write-prepare' (wp) during mkfs.
Add init scripts to bring up volumes at boot.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

uvol is a wrapper-script which allows automated handling of storage
volumes. uvol currently comes with backend support for LVM2 and UBI,
covering practically all options for storage large enough to be
managed (NAND, SPI-NAND, eMMC, SATA, NVME, virtio-blk, ...).

Signed-off-by: Daniel Golle <daniel@makrotopia.org>