[PATCH v2] PCI SRIOV device enable and disable via sysfs

[Donald Dutile <ddutile@redhat.com>]

Currently, VF enablement by SRIOV-capable PCIe devices is done
in driver-specific module parameters.  If not setup in modprobe files,
it requires admin to unload & reload PF drivers with number of desired
VFs to enable.  Additionally, the enablement is system wide: all
devices controlled by the same driver have the same number of VFs
enabled.  Although the latter is probably desired, there are PCI
configurations setup by system BIOS that may not enable that to occur.

Two files are created if a PCIe device has SRIOV support:
sriov_totalvfs -- cat-ing this file returns the maximum number
                  of VFs a PCIe device supports.
sriov_numvfs -- echo'ing a positive number to this file enables 
                & configures this number of VFs for this given PCIe
                device.
	     -- echo'ing 0 to this file disables and deconfigures
                all VFs for this given PCIe device.
             -- cat-ing this file will return the number of VFs
                currently enabled on this PCIe device.

VF enable and disablement is invoked much like other PCIe
configuration functions -- via a registered callback in the driver,
i.e., probe, release, etc.  In this case, sriov_configure

PATCH v1->v2:
-- incorporate more feedback from Ben Hutchings.
-- (hopefully) correct From & Signed-by for Yinghai Lu's patches (1/8 & 2/8)

RFC V3->PATCH:
-- incorporate feedback from Ben Hutchings.
-- clean up poor RFC patches & sanitize through checkpatch.pl

RFC v2->v3:
-- change the file names to reflect the names used in the SRIOV spec
-- change to a single file for enable & disable; 
   change driver interface to a single interface.
-- add more informative messages on failures
-- add a core method that a driver can invoke to modify
   the totalvfs reported & supported by a driver.
-- a set of patches for ixgbe provided by Greg Rose to use the
   new interfaces; the last patch modified from the original
   two file, enable/disable interface to the current single file
   enable/disable. Greg will eventually post the final version
   of these patches via Intel's usual process for driver patches.
   Provided here as an example, and enable other SRIOV drivers
   to see how adoption of the interface can be added.

RFC v1->v2:
This patch is based on previous 2 patches by Yinghai Lu
that cleaned up the vga attributes for PCI devices under sysfs,
and uses visibility-checking group attributes as recommended by
Greg K-H.

Signed-off-by: Donald Dutile <ddutile@redhat.com>
---
 drivers/pci/iov.c       |  48 ++++++++++++++++
 drivers/pci/pci-sysfs.c | 179 ++++++++++++++++++++++++++++++++++++++++++++++++++++++----
 drivers/pci/pci.h       |   2 +
 drivers/pci/probe.c     |   1 +
 include/linux/pci.h     |  11 ++++
 5 files changed, 230 insertions(+), 11 deletions(-)