linux-kernel - Re: Add a helper function in PCI IOV to get VF device

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Message-ID: <20100603175643.GY8301@sequoia.sous-sol.org>
Date:	Thu, 3 Jun 2010 10:56:43 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Frank Pan <frankpzh@...il.com>
Cc:	"Williams, Mitch A" <mitch.a.williams@...el.com>,
	Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Yu Zhao <yu.zhao@...el.com>,
	Chris Wright <chrisw@...s-sol.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"David S. Miller" <davem@...emloft.net>,
	Matt Carlson <mcarlson@...adcom.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Add a helper function in PCI IOV to get VF device

* Frank Pan (frankpzh@...il.com) wrote:
> hi Mitch,
> 
> > Frank, I'm not sure what you're trying to accomplish here. All of the information you need is already in sysfs. Given the PF device, you can look at /sys/class/net/ethX/device/virtfnX to get the bus/device/function of each of the VF devices.
> 
> Yes, that's the most funny part. Sysfs can only be traversed in
> usespace. So the thing userspace knows isn't known by driver(pf driver
> have no idea about vf's bdf), while the thing driver knows isn't known
> by userspace(one cannot infer pf's bdf from vf's bdf).
> Please think kernel/userspace as 2 system, they can hardly communicate
> these informations. IMHO give a syscall/ioctl telling these is funny
> and strange.
> 
> > If the VF driver is loaded in your kernel, then given the bus/device/function of the vf device, you can look at /sys/class/net/ethX/device/virtfnX/net to see which interface corresponds to that VF.
> 
> VF driver will never be loaded on physical machine, it can only be
> loaded in a virtual machine. On a physical machine, VF won't have any
> interface.

VF is often loaded on the physical machine.  There's also a networking
specific mechanism for querying and configuring a VF via the PF.

While your patch is simple, it's unclear to me what your end goal is.
The patch itself only adds a function. if you showed how you are
planning to use it, that would really help.

It's especially confusing that you are comparing your patch with
symlinks visible in sysfs.

thanks,
-chris
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