[Qemu-devel] Re: [PATCH 3/3] msi: Store the capability size in PCIDevice

[Michael S. Tsirkin]

On Tue, Nov 02, 2010 at 08:00:38AM -0600, Alex Williamson wrote:
> 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.

Sounds good. Why does this mean you need the capability size?
        bool was_enabled = msi_enabled(dev);
        msi_write_config(..)
        if (was_enabled != msi_enabled(dev)) {
        }

> 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