Symlinks can have priorities now, the priority is assigned to the device
and specified with OPTIONS="link_priority=100". Devices with higher
priorities overwrite the symlinks of devices with lower priorities.
If the device, that currently owns the link goes away, the symlink
will be removed, and recreated, pointing to the next device with the
highest actual priority.
This should solve the issue, that inserting an USB-stick may overwrite the
/dev/disk/by-id/-link of another disk, and removes the entire link after the
USB-stick is disconnected. If no priorities are specified, the new link will
overwrite the current one, and if the device goes away, it will restore
the old link. It should be possible to assign lower priorities to removable
devices, if needed.
In multipath setups, we see several devices, which all connect to the same
volume, and therefore all try to create the same metadata-links. The
different path-devices are combined into one device-mapper device, which also
contains the same metadata. It should be possible, to assign multipath-table
device-mapper devices a higher priority, so path-devices that appear and
disappear, will not overwrite or delete the device-mapper device links.
This scheme is more consistent and makes it obvious if a match happens
against the event device only, or the full chain of parent devices.
The old key names are now:
BUS -> SUBSYSTEMS
ID -> KERNELS
SYSFS -> ATTRS
DRIVER -> DRIVERS
Match keys for the event device:
KERNEL
SUBSYSTEM
ATTR
DRIVER (in a future release, for now the same as DRIVERS)
Match keys for all devices along the parent device chain:
KERNELS
SUBSYSTEMS
ATTRS
DRIVERS
ID, BUS, SYSFS are no longer mentioned in the man page but still work.
DRIVER must be converted to DRIVERS to match the new scheme. For now,
an error is logged, if DRIVER is used. In a future release, the DRIVER
key behaviour will change.
Consecutive "add" events will not remove and recreate the same symlinks
anymore. No longer valid links, like after changing a filesystem label,
will still be removed.
