[gPXE] [PATCH] [virtio] Add virtio block device sanboot support

[Stefan Hajnoczi]

This patch adds virtio block device support alongside the existing iSCSI,
ATA-over-Ethernet, and ramdisk block devices.  The virtio block device provides
storage in virtualized environments.

Using this patch, a gPXE option ROM can boot a QEMU/KVM virtual machine
directly from a virtio block device.

Here is an example QEMU invocation:
qemu -drive if=virtio,file=debian.qcow2 -option-rom gpxe/src/bin/1af41001.rom

SANBOOT_PROTO_VIRTIO_BLK must be defined in config/general.h to enable this
feature.  The gPXE option ROM must be built for PCI ID 1af4:1001.

The sanboot gPXE command is used with the virtio_blk: root path scheme.  The
virtio block device instance is identified by its PCI bus, device, and function
(there could be multiple virtio block devices).

gPXE> sanboot virtio_blk:PCI00:04.0

Perhaps the first available device should be chosen if virtio_blk: is given
without PCI bus, device, and function.  I am open to suggestions on how virtio
block device option ROMs should work.

I have successfully booted Debian testing i386 and FreeDOS 0.84-pre2 under QEMU
0.11.0.

Note that QEMU/KVM can boot from a virtio block device using a separate
non-virtio interface (-drive if=virtio,boot=on,[...]).  This gPXE patch
provides a native virtio block implementation.

While developing this feature, I noticed that the AoE sanboot code leaves a
pointer to a stack value around after it returns.  A commit to fix this is
included.

Stefan Hajnoczi (2):
  [sanboot] Prevent leaking a stack reference for "keep-san" AoE
  [virtio] Add virtio block device sanboot support

 src/arch/i386/interface/pcbios/aoeboot.c        |   54 +++--
 src/arch/i386/interface/pcbios/virtio_blkboot.c |   70 ++++++
 src/config/config.c                             |    3 +
 src/config/general.h                            |    1 +
 src/drivers/block/virtio-blk.c                  |  271 +++++++++++++++++++++++
 src/drivers/block/virtio-blk.h                  |   30 +++
 src/include/gpxe/errfile.h                      |    2 +
 src/include/gpxe/virtblk.h                      |   37 +++
 8 files changed, 447 insertions(+), 21 deletions(-)
 create mode 100644 src/arch/i386/interface/pcbios/virtio_blkboot.c
 create mode 100644 src/drivers/block/virtio-blk.c
 create mode 100644 src/drivers/block/virtio-blk.h
 create mode 100644 src/include/gpxe/virtblk.h