[dm-crypt] concurrency

Michael Kjörling michael at kjorling.se
Sun Mar 27 18:52:26 CEST 2016

On 27 Mar 2016 00:50 +1000, from hughbragg at dodo.com.au (Hugh Bragg):
> Should I be able to use Luks concurrently on a shared filesystem from
> different computers?
> Attempts so far have failed with writes not being seen from the other
> computer until both computers remount the filesystem or reboot.

As a thought experiment, try removing LUKS from the equation. For the
purposes of what you seem to be asking, LUKS is just a part of the
physical storage layer.

Instead of [unencrypted physical storage device + LUKS container]
providing the feature "encrypted storage of user-selected data",
consider the case [self-encrypting physical storage device] which
provides the same feature "encrypted storage of user-selected data"
but this time without involving LUKS or dm-crypt.

_Would you expect what you have in mind to work after making that
single change?_

If not, then there is no reason to expect it to suddenly start working
when you introduce an additional component (LUKS) into the _physical_
storage stack. And as far as the file system is concerned, LUKS very
much _is_ a part of the physical storage stack. (There would be
nothing _architecturally_ weird with a HBA that itself runs LUKS and
exposes the decrypted container while writing the encrypted data to
the actual physical storage device. It would come with some fairly
serious design challenges if one wants to make it secure, however.)

Michael Kjörling • https://michael.kjorling.semichael at kjorling.se
                 “People who think they know everything really annoy
                 those of us who know we don’t.” (Bjarne Stroustrup)

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