[Xen-devel] PV drivers on HVM using Xen 4.1.1

[Alex Bligh <alex@xxxxxxxxxxx>]

I think I've found one reason why we can't get PV block drivers on HVM
domUs working on Xen 4.1.1 - whether we use a pvops or a xenlinux
domU kernel.

We are using a line like:

 disk = [ "tap:aio:/tmp/centos-pvd.img,xvda,w" ]

We are using effectively a standard 3.0 kernel. Config options including
the word XEN are below.

We do not see blktapctrl starting in Xen 4.1.1 dom0, but it does
start in Xen3. In fact as far as I can tell the Ubuntu Xen4 package
does not contain blktapctrl at all (which would explain why it doesn't
start). Do we need this?

It has been suggested that we don't need this, but we do need a kernel
module that provides blktap.

 http://www.vr.org/knowledgebase/1112/Xen-Paravirt-Ops.html

suggests these might be queued for the non-existent "2.6.40", but
it's suggested these aren't in 3.0.

 http://wiki.xensource.com/xenwiki/XAPI_on_debian

suggests there are dmks modules available, but that blktap is currenly
only 32 bit. Can that be correct?

Isn't this what blkback does?

domU config is below. Note the very same VM with the same config file
works just fine on xen 3.3.1. This domU is Centos 2.6.18 with
unmodified_drivers xenlinux type kernel (as supplied by Centos). Every
other kernel we've tried does the same, save that modern ones also
unplug the emulated devices so no disks appear as well.

PV nics work fine.

--
Alex Bligh

root@xen4:/home/ubuntu/kernel# fgrep XEN /boot/config-3.0.0-12-server
CONFIG_XEN=y
CONFIG_XEN_DOM0=y
CONFIG_XEN_PRIVILEGED_GUEST=y
CONFIG_XEN_PVHVM=y
CONFIG_XEN_MAX_DOMAIN_MEMORY=128
CONFIG_XEN_SAVE_RESTORE=y
# CONFIG_XEN_DEBUG_FS is not set
# CONFIG_XEN_DEBUG is not set
CONFIG_PCI_XEN=y
CONFIG_XEN_PCIDEV_FRONTEND=m
CONFIG_XEN_BLKDEV_FRONTEND=m
CONFIG_XEN_BLKDEV_BACKEND=m
CONFIG_NETXEN_NIC=m
CONFIG_XEN_NETDEV_FRONTEND=m
CONFIG_XEN_NETDEV_BACKEND=m
CONFIG_INPUT_XEN_KBDDEV_FRONTEND=m
CONFIG_HVC_XEN=y
CONFIG_XEN_WDT=m
CONFIG_XEN_FBDEV_FRONTEND=m
CONFIG_XEN_BALLOON=y
CONFIG_XEN_SCRUB_PAGES=y
CONFIG_XEN_DEV_EVTCHN=m
CONFIG_XEN_BACKEND=y
CONFIG_XENFS=m
CONFIG_XEN_COMPAT_XENFS=y
CONFIG_XEN_SYS_HYPERVISOR=y
CONFIG_XEN_XENBUS_FRONTEND=m
CONFIG_XEN_GNTDEV=m
CONFIG_XEN_GRANT_DEV_ALLOC=m
CONFIG_XEN_PLATFORM_PCI=m
CONFIG_SWIOTLB_XEN=y

root@xen4:/home/ubuntu/kernel# lsmod | fgrep -i xen
xen_netfront           26671  0
xen_blkfront           26261  0
xen_wdt                13525  0
xen_gntalloc           13321  0
xenbus_probe_frontend    13232  2 xen_netfront,xen_blkfront,[permanent]
xen_gntdev             17676  2
netxen_nic             97283  0
xen_netback            27854  0 [permanent]
xen_blkback            23177  0 [permanent]
xen_evtchn             13172  5
xenfs                  18311  1

Guest config looks like this, though we've used xvda and hda

root@xen4:/home/ubuntu/kernel# cat !$
cat /etc/xen/centos5-pvd
name = "centos5-pvd-xen4"
uuid = "6d72aff9-8f53-beb7-c71c-89e72b93193e"
maxmem = 512
memory = 512
vcpus = 2
builder = "hvm"
#kernel = "/usr/lib/xen/boot/hvmloader"
boot = "c"
pae = 1
acpi = 1
apic = 1
localtime = 0
on_poweroff = "destroy"
on_reboot = "restart"
on_crash = "restart"
#device_model = "/usr/lib64/xen/bin/pv-qemu-dm"
#device_model = "/usr/lib/xen/bin/stubdom-dm"
#sdl = 0
#vnc = 1
vnclisten="0.0.0.0"
keymap="en-gb"
#vncunused = 1
#vncdisplay = "3"
vfb = [ "type=vnc,vncunused=1,keymap=en-gb" ]
disk = [ "file:/root/Iain2011/centos-pvd.img,xvda,w" ]
vif = [ 
"mac=00:16:3e:00:a5:58,bridge=br0,type=foo","mac=00:16:3e:00:a5:58,bridge=br0,type=ioemu" 
]
serial = "pty"




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