On Thu, 26.08.10 23:11, Diego Calleja (dieg...@gmail.com) wrote: > Hi, while reading the documentation I noticed that the "What" parameter > of .swap units doesn't seems to be able to take an UUID/label. Well, that's > just a TODO...what worried me is that: > > "Swap units must be named after the devices they control" > > Isn't this rule incompatible with UUIDs/labels?
Actually no, it isn't. The reason for this is a bit convoluted though: A device that comes and goes can do so under various names, and these names might be aliases of different devices at varying times. Example: you plug in a device with a swap partition with the uuid of X. At that time the partition is available in the system as kernel device /dev/sdf6. Then, later on you unplug the device, plug in some other stuff, then plug it in again, now it is /dev/sdg6. So the first time the device /dev/sdf6 was the same as /dev/disk/by-uuid/X, and the second time /dev/sdg6 was the same as /dev/disk/by-uuid/X. If an entry in fstab now refers to uuid X this actually points to two different devices depending on the time. And that's a bit weird. To deal with this we decided to expose every single of the device names by a different device unit in systemd. i.e. there is dev-sdf6.device, there is dev-sdg6.device and there is dev-disk-by-uuid-X.device, and they are maintained seperately and all references to them are seperately stored as well. However, depending on the time, dev-disk-by-uuid-X.device might actually follow dev-sdf6.device or dev-sdg6.device in its state machine. (Note that normally systemctl won't show you units that "follow" other units, unless you pass --all) So long story short, if the swap stuff is properly implemented, then a uuid/label swap unit will refer to one specific device which is then called exactly like the swap unit. At that device might then follow different other units at different times. Lennart -- Lennart Poettering - Red Hat, Inc. _______________________________________________ systemd-devel mailing list systemd-devel@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/systemd-devel
