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From: Alex Williamson <alex.williamson@redhat.com>
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Date: Tue, 02 Nov 2010 08:00:38 -0600
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Subject: [Qemu-devel] Re: [PATCH 3/3] msi: Store the capability size in
	PCIDevice
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To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: yamahata@valinux.co.jp, qemu-devel@nongnu.org

On Tue, 2010-11-02 at 11:25 +0200, Michael S. Tsirkin wrote:
> On Mon, Nov 01, 2010 at 11:37:53PM -0600, Alex Williamson wrote:
> > Avoid needing to get the MSI capability flags every time we need to
> > check the capability length.  This also makes it accessible outside
> > of msi.c, making it easier for users to filter config space writes
> > using msi_cap and msi_cap_size.
> 
> I think for this last use-case, we are better off with returning a
> boolean from msi_write_config which tells us whether the write is in
> range. This has the advantage in that it will also work well for other
> capabilities. Or second best, if that is insufficient for some reason,
> export an msi_cap_size function.

Returning whether the write was in range isn't enough.  For device
assignment, I need to know whether the capability was enabled or
disabled.  This currently means checking the enable state before and
after calling msi_write_config and doing the appropriate backend setup.
I think the only way I could blindly call the msi/x write config
routines is if we init the capability with enable/disable callbacks.
I'd be ok with an msi_cap_size function if we don't want to go that far
too.  What do you prefer?  Thanks,

Alex