Re: [Xen-devel][PATCH]ioemu:

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Zhang, Yang writes ("[Xen-devel][PATCH]ioemu:"):
> The default cache mode has been changed from write-back to
> write-through after merging in Oct 23. And this make the guest
> boot slowly with qcow. This patch changes it to write-back again.

I'm slightly puzzled by this because the effect is to add O_DSYNC to
the flags passed to open().  But this should effectively be the
default for us anyway because we implement IDE cache control, which
defaults to cacheing off.  Does your guest enable the IDE cache ?

However I agree that passing BDRV_O_CACHE_WB, to disable O_DSYNC,
would be correct at least for the non-stubdom case.  Does O_DSYNC even
have any effect in stubdom ?  I would have expected not.

Why did you set BDRV_O_RDONLY as well ?  That seems wrong to me.  In
fact, it worries me that your guest could boot at all with
BDRV_O_RDONLY forced on.  Also your comment seems somewhat confused;
the code path your patching is used for all disk opens and not just
snapshots.

I'll hold off doing anything for now until the situation becomes
slightly clearer.  Thanks for your contribution.  (And next time
please include a Signed-Off-By.)

Regards,
Ian.

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