Re: [Qemu-devel] [PATCH v5 0/8] Add metadata overlap checks

[Max Reitz <mreitz@redhat.com>]

On 2013-09-13 14:29, Eric Blake wrote:
> On 09/13/2013 04:23 AM, Max Reitz wrote:
>> […]
>> I think, we should first take care of the command line interface and
>> about QMP later (that is, if you agree on generally allowing
>> modification of the qcow2 runtime options through QMP). There, we could
>> offer both one boolean per mask element and an integer option, probably
>> the boolean flags taking precedence.
> I'm fine if it is JUST a command-line parameter (all-or-nothing, turned
> on when you boot qemu, and not something we can be changing on the fly).
>   But if we ever do want live changing via QMP, do NOT expose it as a raw
> int, but only as named bools.
Another idea: Instead of providing an integer for "shorthand" 
manipulations, what do you think of a string parameter (such as -o 
cache=foo right now, although I do know -o cache isn't even document 
anymore and provided only for compatibility reasons, it seems to me) 
which will automatically be translated to the right settings? I'm 
thinking of:
  - overlap-check=none (no checks at all)
  - overlap-check=constant (only checks who can be performed in constant 
time, i.e., main header, active L1, refcount table and snapshot table)
  - overlap-check=cached (only checks which don't require disk access, 
i.e. the current (and as I'd propose, future) default)
  - overlap-check=all (all checks, including those requiring disk access 
(i.e., overlaps on inactive L2 tables))

These would then provide templates which can be further refined through 
the booleans (as is the case with -o cache right now).


Max