From mboxrd@z Thu Jan  1 00:00:00 1970
From: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <royger@FreeBSD.org>
Subject: Re: Hotplugged devices in Xen 4.5 and domain reboot
Date: Tue, 1 Dec 2015 18:52:15 +0100
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To: Iurii Mykhalskyi <iurii.mykhalskyi@globallogic.com>, Wei Liu <wei.liu2@citrix.com>
Cc: Pavlo Suikov <pavlo.suikov@globallogic.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, Ian Campbell <ian.campbell@citrix.com>, Andrii Anisov <andrii.anisov@globallogic.com>, xen-devel@lists.xen.org
List-Id: xen-devel@lists.xenproject.org

El 01/12/15 a les 17.48, Iurii Mykhalskyi ha escrit:
>> Does something like the following work? If not, could you paste the
>> error when running it with -vvv.
>>
>> xl block-attach DomU
>> format=raw,vdev=hdc,access=rw,backend=DomD,target=/path/to/dev
> In dom0 we have next issue:
> /libxl: error: libxl_device.c:283:libxl__device_disk_set_backend: Disk
> vdev=xvda10 failed to stat: /dev/sda1: No such file or directory//-
> /this issue occurs due to missing /dev/sda1 device (all hardware are
> placed in DomD domain).

I'm not sure how can you get to this path, the libxl chunk in 
stable-4.5 is:

271     if (disk->format == LIBXL_DISK_FORMAT_EMPTY) {
272         if (!disk->is_cdrom) {
273             LOG(ERROR, "Disk vdev=%s is empty but not cdrom", disk->vdev);
274             return ERROR_INVAL;
275         }
276         memset(&a.stab, 0, sizeof(a.stab));
277     } else if ((disk->backend == LIBXL_DISK_BACKEND_UNKNOWN ||
278                 disk->backend == LIBXL_DISK_BACKEND_PHY) &&
279                disk->backend_domid == LIBXL_TOOLSTACK_DOMID &&
280                !disk->script) {
281         if (stat(disk->pdev_path, &a.stab)) {
282             LOGE(ERROR, "Disk vdev=%s failed to stat: %s",
283                         disk->vdev, disk->pdev_path);
284             return ERROR_INVAL;
285         }
286     }

So it seems that block-attach is ignoring the 'backend=foo' field in 
the disk configuration?

Can you paste the full output of the execution with -vvv?

Roger.