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

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Message-ID: <20180402141729.4576365d@cakuba.netronome.com>
Date:   Mon, 2 Apr 2018 14:17:29 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Christoph Hellwig <hch@...radead.org>
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 Fri, 30 Mar 2018 04:49:05 -0700, Christoph Hellwig wrote:
> 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.

Ugh, I took me a while to understand what I meant myself...  So what I
meant is that this should generally work:

# cat .../sriov_totalvfs > .../sriov_numvfs

I.e. one should be able to "enable" the number of VFs advertised in
sriov_totalvfs.  I will rephrase!

> > 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.

I think I may just go with what I think Alex is suggesting and "unset"
the value to total_VFs.