disk Partition label changes and reflecting them in /dev/disks-by-label/

disk Partition label changes and reflecting them in /dev/disks-by-label/

[Linda Walsh]

 

If I have a disk with no mounted partitions and I change the partition 
order,
the OS will re-read the new partition and life goes on.

However, if I create or change a new disk label, it seems label programs
(and users) should have an option to reread the labels after the 
modification.

Ideally any prog that changes a Label or UUID would trigger an update
of what's in /dev/disks to reflect the new 'reality'.

Currently, I go through through a seemingly bizarre ritual of invoking
unmounting all other partitions on the same disk, then becoming root,
running fdisk on the disk, then just exiting with "w".  This triggers
a reread of not only the partition table, but also the new labels. 

However, I find this far less than ideal.  Is there a better way, or could
there be a better way to update new Labels and UUID's that are actually
on a disk -- perhaps even as an ordinary user command (since it would be
a read-only operation on the disk that simply updates /dev/disk to reflect
what's really there -- Especially being able to change only the label (or
UUID), only on one partition w/o having to actually unmount other file 
systems
on the disk....?

Already implemented?  Or doable?  Or bad idea?

Thanks,
-linda

Re: disk Partition label changes and reflecting them in /dev/disks-by-label/

[Alan Jenkins]

On 7/19/09, Linda Walsh <lkml@tlinx.org> wrote:
>
>
> If I have a disk with no mounted partitions and I change the partition
> order,
> the OS will re-read the new partition and life goes on.
>
> However, if I create or change a new disk label, it seems label programs
> (and users) should have an option to reread the labels after the
> modification.
>
> Ideally any prog that changes a Label or UUID would trigger an update
> of what's in /dev/disks to reflect the new 'reality'.
>
> Currently, I go through through a seemingly bizarre ritual of invoking
> unmounting all other partitions on the same disk, then becoming root,
> running fdisk on the disk, then just exiting with "w".  This triggers
> a reread of not only the partition table, but also the new labels.
>
> However, I find this far less than ideal.  Is there a better way, or could
> there be a better way to update new Labels and UUID's that are actually
> on a disk -- perhaps even as an ordinary user command (since it would be
> a read-only operation on the disk that simply updates /dev/disk to reflect
> what's really there -- Especially being able to change only the label (or
> UUID), only on one partition w/o having to actually unmount other file
> systems
> on the disk....?
>
> Already implemented?  Or doable?  Or bad idea?
>
> Thanks,
> -linda

Already implemented :-).

The latest version of udev listens for inotify events on block
devices.  When a utility writes to the block device (or rather, when
it closes it after opening it for writing), Udev will synthesize a
"change" event.  The standard udev rules will re-check the device, and
update the links under /dev/disk to reflect changes in labels etc.

Alan

Re: disk Partition label changes and reflecting them in /dev/disks-by-label/

[Mark Lord]

Alan Jenkins wrote:
>
> The latest version of udev listens for inotify events on block
> devices.  When a utility writes to the block device (or rather, when
> it closes it after opening it for writing), Udev will synthesize a
> "change" event.  The standard udev rules will re-check the device, and
> update the links under /dev/disk to reflect changes in labels etc.
..

Yes, it seems to catch LABEL changes just fine.

On a related note:
But not UUID changes for some reason (?).