Anthony Liguori wrote:
On 05/16/2011 03:23 PM, Christoph Hellwig wrote:
Why are you even trying this again? As explained very clearly last
time you
can't change from a writeback-style to a write-through style I/O from
the monitor without creating massive data integrity problems.
To further clarify:
Today cache=none|writethrough|writeback does two things. It:
1) Changes the WCE flag that's visible to the guest
2) Determines whether the host page cache is used for doing guest I/O
As Christoph is very correct in pointing out, we cannot change (1) at
run time because this is guest visible. You will break a guest if you
do this.
ok
But it's still desirable to be able to change (2) at run time. Before
we can do this properly though, we need to separate out the logic for
setting (1) vs. (2).
Will go through the code in detail to understand handling of (1) and (2).
And ideally, we would allow (1) to be changed by the guest itself at
run time which allows for full dynamic control. This is what he's
referring to below.
Regards,
Anthony Liguori
See my
patchset that allows changing this from the guest for how it should be
done - I just need to get back and revisit the virtio protocol support
for it.
