[dm-devel] [PATCH 9/9] dm-integrity: recalculate checksums

[Zdenek Kabelac]

Dne 3.7.2018 v 20:24 Mikulas Patocka napsal(a):
> 
> 
> On Tue, 3 Jul 2018, Milan Broz wrote:
> 
>> On 07/03/2018 03:21 PM, Mike Snitzer wrote:
>>>>
>>>> Should we even have the possibility to stop recalculating?
>>>>
>>>> If the device was recalculating and we activate it without the
>>>> "recalculate" flag, what should it do? If the user reads data that haven't
>>>> been recalculated yet, we could:
>>>> 1. return an error
>>>> 2. ignore the non-recalculated checksum and return data
>>>> 3. continue with recalculating even if the flag "recalculate" is not present
>>>>
>>>> In my opinion, the option 3 is the best. Option 1 makes the device
>>>> unreliable and option 2 makes the device silently lose the integrity
>>>> protection.
>>>
>>> Yes, option 3.  But you could even error out on table load; though that
>>> may be too unforgiving.. reality is userspace needs to account for
>>> staying in recalculating mode until it is complete.
>>
>> I do not think table load error is the way to go.
>>
>> Can we activate dmintegrity read-only (for example with read-only backend device)
>> that is not yet fully recalculated?
> 
> There's no read-only activation because the journal must be replayed. Most
> journaled filesystems also don't provide read-only activation because they
> need to replay the journal.

There would  always an option to use some temporary space with old snapshot 
COW target - and use read-only device on top of that.

Zdenek