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Date:      Mon, 5 Dec 2016 20:48:00 -0700
From:      Nathan Friess <nathan.friess@gmail.com>
To:        freebsd-xen@freebsd.org
Subject:   11-RELEASE acting as vbd backend
Message-ID:  <247e5b6c-2713-27cf-f8fa-61e55c9e2025@gmail.com>

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Hi,

After upgrading a FreeBSD domU from 10.3-RELEASE to 11-RELEASE, it seems 
that FreeBSD can no longer act as a vbd backend for other domUs.


***
My setup before upgrading:

Xen 4.4

dom0: Linux (Debian) with a custom compiled 4.2 kernel

FreeBSD domU: FreeBSD 10.3-RELEASE-p7 in hvm mode.
Filesystem is ZFS, with zvols created for other domUs.
xen-guest-tools-4.2.2_1 is installed through pkg.

Other domU: Linux with the same compiled 4.2 kernel in pv mode.  Xen 
disk configuration is 
'format=raw,vdev=xvda1,backendtype=phy,backend=FREEBSD,access=w,target=/dev/zvol/.../rootfs'
***


***
Now that FreeBSD 11-RELEASE is out I upgraded it in place.  After 
upgrading FreeBSD the other Linux domU can no longer find /dev/xvda1 to 
mount as its root.  It hangs at boot waiting for the device to appear.

While the Linux domU is waiting for the vbd I ran xenstore-ls in dom0 to 
see what is going on.  The backend appears in FreeBSD and the frontend 
in the Linux domU, but FreeBSD shows state=2 and Linux shows state=3.


FreeBSD backend:

/local/domain/6/backend/vbd = ""   (n0,r6)
/local/domain/6/backend/vbd/7 = ""   (n0,r6)
/local/domain/6/backend/vbd/7/51713 = ""   (n6,r7)
/local/domain/6/backend/vbd/7/51713/frontend = 
"/local/domain/7/device/vbd/51713"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/params = "/dev/zvol/.../rootfs"   
(n6,r7)
/local/domain/6/backend/vbd/7/51713/script = "/etc/xen/scripts/block"   
(n6,r7)
/local/domain/6/backend/vbd/7/51713/frontend-id = "7"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/online = "1"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/removable = "0"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/bootable = "1"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/state = "2"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/dev = "xvda1"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/type = "phy"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/mode = "w"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/device-type = "disk"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/feature-barrier = "1"   (n6,r7)
/local/domain/6/backend/vbd/7/51713/feature-flush-cache = "1" (n6,r7)
/local/domain/6/backend/vbd/7/51713/max-ring-page-order = "5" (n6,r7)


Linux frontend:

/local/domain/7/device/vbd = ""   (n0,r7)
/local/domain/7/device/vbd/51713 = ""   (n7,r6)
/local/domain/7/device/vbd/51713/backend = 
"/local/domain/6/backend/vbd/7/51713"   (n7,r6)
/local/domain/7/device/vbd/51713/backend-id = "6"   (n7,r6)
/local/domain/7/device/vbd/51713/state = "3"   (n7,r6)
/local/domain/7/device/vbd/51713/virtual-device = "51713"   (n7,r6)
/local/domain/7/device/vbd/51713/device-type = "disk"   (n7,r6)
/local/domain/7/device/vbd/51713/protocol = "x86_64-abi"   (n7,r6)
/local/domain/7/device/vbd/51713/ring-ref = "8"   (n7,r6)
/local/domain/7/device/vbd/51713/event-channel = "15"   (n7,r6)
/local/domain/7/device/vbd/51713/feature-persistent = "1"   (n7,r6)



When the vbd was working in 10.3, the backend also shows the following:

/local/domain/8/backend/vbd/9/51713/hotplug-status = "connected" (n8,r9)
/local/domain/8/backend/vbd/9/51713/sectors = "41943040"   (n8,r9)
/local/domain/8/backend/vbd/9/51713/info = "0"   (n8,r9)
/local/domain/8/backend/vbd/9/51713/sector-size = "512"   (n8,r9)
***


In case there is a version incompatibility with the new FreeBSD, I later 
upgraded Xen to 4.7 and dom0 to a Linux 4.4 kernel.  This did not help.

How might I get this setup working again?

Thanks,

Nathan




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