Hallo, Hugo,
Du meintest am 03.01.13:
[...]
>>> Trying to use filesystem labels to give unique and stable device
>>> IDs is the wrong tool for the job.
>> I beg to differ. On my machines it's the simpliest way, and it's a
>> sure way.
> No, because *it* *doesn't* *work*. This is not a bug. This is how
> things have always behaved -- you're relying on an assumption (one FS
> per device) which simply isn't true any longer.
No - I don't rely on such an assumption.
In the special case I'm just working with I want to use the whole disk
only for btrfs.
In other cases I work with partitions, and there is just the same
problem: at least "blkid" and "findfs" don't work when more than 1
device has the same label (p.e. /dev/sda3 and /dev/sdc5).
>> And how is the way for a system which doesn't use "udev"?
> There isn't one ready-made. Your options are:
> * run udev
> * write something which uses (e.g.) SMART information on block
> devices to extract a unique ID, and convert that into a stable
> device label (which is effectively what udev does)
Sorry - I don't need the "unique ID" for the machines. I can use (p.e.)
e2label /dev/sda3 Var
for labelling an ext2/3/4 partition. Works like a charm, especially for
USB disks.
> * find some piece of the device which isn't going to be overwritten
> by partition tables, GPTs, filesystems, or other kinds of
> metadata, and write your label into there; again, you will need to
> develop your own tool for reading/writing this information
Sorry - that's not necessary. When I connect the disk then I can search
with "findfs" without having mounted any partition.
>> Labelling via "btrfs filesystem label <device> <label>" works well.
> Clearly it doesn't, because you're having problems with it.
No - not at all!
I've only problems when I use the "-L" option of "mkfs.btrfs" together
with more than 1 device in the "mkfs.btrfs" command.
> The
> behaviour where only one device in the FS gets the label, immediately
> after a btrfs label command, is a bug -- *all* of the devices in the
> FS should get the label. You're trying to rely on the behaviour of a
> bug, not on the designed behaviour of the system.
What works:
Building the filesystem with "mkfs.btrfs", without the "-L" option
Then (p.e.)
btrfs filesystem label <device> <label>
(unmounted system)
Then I can check the existence (not only for btrfs formatted disks) with
findfs LABEL=<label> && mount LABEL=<label> <mountpoint>
As mentioned: works not only with btrfs, works fine especially for USB
disks. I don't need any UUID etc. for this way of identyfying. I don't
need to change the mount directive when I change a smaller disk to a
bigger disk.
Viele Gruesse!
Helmut
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
