linux-kernel - Re: [PATCH] Create sysfs entries for PCI VPDI and VPDR tags

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Message-ID: <CAC1AzddUqEScGgUqPxa8CgLSH3gynVcj71vMNn6b-Roi2YTRUQ@mail.gmail.com>
Date:	Fri, 19 Feb 2016 08:07:13 -0600
From:	Jordan Hargrave <jharg93@...il.com>
To:	Hannes Reinecke <hare@...e.de>
Cc:	Jordan Hargrave <Jordan_Hargrave@...l.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, alexander.duyck@...il.com,
	linux-pci@...r.kernel.org, babu.moger@...cle.com,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Create sysfs entries for PCI VPDI and VPDR tags

On Fri, Feb 19, 2016 at 4:00 AM, Hannes Reinecke <hare@...e.de> wrote:
>
> On 02/18/2016 09:04 PM, Jordan Hargrave wrote:
> > The VPD-R is a readonly area of the PCI Vital Product Data region.
> > There are some standard keywords for serial number, manufacturer,
> > and vendor-specific values.  Dell Servers use a vendor-specific
> > tag to store number of ports and port mapping of partitioned NICs.
> >
> > info = VPD-Info string
> > PN = Part Number
> > SN = Serial Number
> > MN = Manufacturer ID
> > Vx = Vendor-specific (x=0..9 A..Z)
> >
> > This creates a sysfs subdirectory in the pci device: vpdattr with
> > 'info', 'EC', 'SN', 'V0', etc. files containing the tag values.
> >
> > Signed-off-by: Jordan Hargrave <Jordan_Hargrave@...l.com>
> Hmm. Can we first get an agreement on the PCI VPD parsing patches
> I've posted earlier?
> VPD parsing is really tricky, and we should aim on making the
> read_vpd function robust enough before we begin putting things into
> sysfs.
>
> Also, I'm not utterly keen on this patchset.
> The sysfs space is blown up with tiny pieces of information, which
> can easily gotten via lspci, too.
>
> Also, to my knowledge it's perfectly valid to _write_ to the VPD, in
> which case the entire sysfs attribute setup would be invalided.
> How do you propose to handle that?
>

This patch only reads the attributes from VPD-I and VPD-R areas, not
the VPD-W (read write) area.
The VPD-W data is located after the VPD-I and VPD-R area  So nothing
in these attributes should change.

The main reason I want this is for replacing biosdevname (ethernet
naming) functionality and getting
the same functionality into the kernel and systemd.  Systemd doesn't
want to do vpd parsing, and
reading the vpd can take a very long time on some devices, causing
systemd to timeout.  Another
disadvantage of it being in userspace is for devices using SR-IOV.  In
those devices the vpd only
exists for the physfn devices but not the virtual devices.  A
userspace program device will have to
read the entire VPD for each physical and virtual PCI device.

Logic is something like this:
if (open("/sys/bus/pci/devices/X/physfn/vpd", O_RDONLY) < 0)
   if (open("/sys/bus/pci/devices/X/vpd", O_RDONLY) < 0)
     return;
}
parsevpd(fd);

Specifically it is parsing one of the Vx attributes for a 'DCM' or
'DC2' string that contain a mapping from
NIC ports and partitions to PCI device

> Cheers,
>
> Hannes
>
> --
> Dr. Hannes Reinecke                Teamlead Storage & Networking
> hare@...e.de                                   +49 911 74053 688
> SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
> HRB 21284 (AG Nürnberg)