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Date: Mon, 13 Jul 2015 17:31:26 +0100
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH v7 21/42] postcopy: OS support test
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To: Juan Quintela <quintela@redhat.com>
Cc: aarcange@redhat.com, yamahata@private.email.ne.jp, liang.z.li@intel.com, qemu-devel@nongnu.org, luis@cs.umu.se, amit.shah@redhat.com, pbonzini@redhat.com, david@gibson.dropbear.id.au

* Juan Quintela (quintela@redhat.com) wrote:
> "Dr. David Alan Gilbert (git)" <dgilbert@redhat.com> wrote:
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> >
> > Provide a check to see if the OS we're running on has all the bits
> > needed for postcopy.
> >
> > Creates postcopy-ram.c which will get most of the other helpers we need.
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> Reviewed-by: Juan Quintela <quintela@redhat.com>
> 
> I am guessing that test is ok, but we are doing the test each time that
> we change the function.  We always end calling that kind of functions in
> several places.  Shouldn't be good to rename the function to
> __postcopy_ram_supported_by_host()
> 
> and do a toplevel function that is:
> 
> bool postcopy_ram_supported_by_host(void)
> {
>         static bool first_time = true;
>         static supported = false;
> 
>         if (firt_time) {
>            first_time = false;
>            supported = __postcopy_ram_supported_by_host()
>         }
>         return supported;
> }
> 
> Notice that I don't know how slow the mmap + usefault thing is, but I
> guess that the values would not change while running, no?

Since we only call this once, at the start of an incoming migration,
it seems overkill to do that.

Dave

> 
> It has a review-by because I don't see anything wrong with it.
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK