linux-kernel - Re: How to get the number of VFs assigned to the guests in XEN

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Date:	Wed, 20 Aug 2014 06:46:11 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	Sreekanth Reddy <sreekanth.reddy@...gotech.com>
Cc:	linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, konrad.wilk@...cle.com,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Christoph Hellwig <hch@....de>, boris.ostrovsky@...cle.com,
	Sathya Prakash <sathya.prakash@...gotech.com>,
	Nagalakshmi Nandigama <nagalakshmi.nandigama@...gotech.com>
Subject: Re: How to get the number of VFs assigned to the guests in XEN

On Wed, 2014-08-20 at 16:39 +0530, Sreekanth Reddy wrote:
> HI,
> 
> For SRIOV support, currently in the KVM environment, mpt3sas driver
> can use the API pci_vfs_assigned() to know the number of VFs that are
> currently assigned to the running VMs. So that during the PF driver
> unload time, if the return value of this API is greater than zero the
> our driver won't call the pci_disable_sriov() to disable the VFs.
> 
> Now for the same purpose in XEN environment, is there any API similar
> to pci_vfs_assigned() which the low lever device driver can use to
> know 'the number of VFs that are currently assigned to the running
> VMs'. In XEN environment this API pci_vfs_assigned() will return
> always zero even though VFs are assigned to the running VMs.

Note that pci_vfs_assigned() assigned is only used by legacy KVM device
assignment and primarily as a workaround for not using an actual
host-based device driver to manage device ownership.  When using
VFIO-based device assignment with KVM, pci_vfs_assigned() is not
updated.  Please don't rely on this interface.  Thanks,

Alex

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