netdev - Re: [PATCH] PCI: allow drivers to limit the number of VFs to 0

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Message-ID: <20180330114905.GA10246@infradead.org>
Date:   Fri, 30 Mar 2018 04:49:05 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        netdev@...r.kernel.org, Sathya Perla <sathya.perla@...adcom.com>,
        Felix Manlunas <felix.manlunas@...iumnetworks.com>,
        alexander.duyck@...il.com, john.fastabend@...il.com,
        Jacob Keller <jacob.e.keller@...el.com>,
        Donald Dutile <ddutile@...hat.com>, oss-drivers@...ronome.com
Subject: Re: [PATCH] PCI: allow drivers to limit the number of VFs to 0

On Thu, Mar 29, 2018 at 11:22:31AM -0700, Jakub Kicinski wrote:
> Some user space depends on driver allowing sriov_totalvfs to be
> enabled.

I can't make sene of this sentence.  Can you explain what user space
code depends on what semantics?  The sriov_totalvfs file should show
up for any device supporting SR-IOV as far as I can tell.

>
> For devices which VF support depends on loaded FW we
> have the pci_sriov_{g,s}et_totalvfs() API.  However, this API
> uses 0 as a special "unset" value, meaning drivers can't limit
> sriov_totalvfs to 0.  Change the special value to be U16_MAX.
> Use simple min() to determine actual totalvfs.

Please use a PCI_MAX_VFS or similar define instead of plain U16_MAX or ~0.