linux-kernel - Re: [PATCH 5/7] vfio: Use new interfaces for MSI/MSI-X enablement

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Date:	Wed, 8 Jan 2014 08:42:25 +0100
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH 5/7] vfio: Use new interfaces for MSI/MSI-X enablement

On Tue, Jan 07, 2014 at 11:34:13AM -0700, Alex Williamson wrote:
> On Tue, 2014-01-07 at 19:05 +0100, Alexander Gordeev wrote:
> > This update also fixes a bug when deprecated pci_enable_msix()
> > and pci_enable_msi_block() functions return a positive return
> > value which indicats the number of interrupts that could have
> > been allocated rather than a successful allocation. The driver
> > misinterpreted this value and assumed MSI-X/MSIs are enabled,
> > although in fact it were not.
> 
> No, the driver interpreted it correctly, which is why anything other
> than zero is handled as an error.  This patch looks incorrect if the new
> interfaces follow the same return convention.  Thanks,

The new interfaces differ wrt the return value - it is eigher a negative
error code or a positive number of successfuly allocated vectors. 

If the user level makes use of a number of vectors that could have been
allocated then it should cease doing it, since only 0 or a negative error
code is returned after this update.

The changelog is incorrect as the driver indeed bailes out on positive
return values. I will send a updated version.

> Alex

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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