RE: Daily Xen-HVM Builds: cs9226

[Daniel Stekloff <dsteklof@us.ibm.com>]

On Thu, 2006-03-16 at 13:25 +0800, Yu, Ping Y wrote:
> Daniel,
> 
> Currently, HVM support multiple disks in QEMU configure, and you can add
> extra disks by configuring options in "disk", for example,
> disk = [ 'file:/var/images/min-el3-i386.img,ioemu:hda,w', 'file:/var/images/min-el3-i386_2.img,ioemu:hdb,w' ]
> Does it meet your requirement?


My requirement for what? I know HVM domains can support more than one
disk image, the idea is to get xm-test to automate creating disk images
for testing HVM domains. My plan is to eventually is to use
device-mapper to present a read only root image, that all the xm-test
HVM test domains will share and then add writable partitions as needed
to test domains. 


> Currently problem is that strict check is added in VBD and forbid one 
> image for multiple HVM and all those test cases in xm-test failed, see information
>  below:
> 
> [dom0] Running `xm create /tmp/xm-test.conf'
> Using config file "/tmp/xm-test.conf".
> Error: Device 768 (vbd) could not be connected.
> File /opt/vmm/control_panel/xm-test/ramdisk/disk.img is loopback-mounted through /dev/loop0,
> which is mounted in a guest domain,
> and so cannot be mounted now.
> Failed to create test domain because:
> Using config file "/tmp/xm-test.conf".
> Error: Device 768 (vbd) could not be connected.
> File /opt/vmm/control_panel/xm-test/ramdisk/disk.img is loopback-mounted through /dev/loop0,
> which is mounted in a guest domain,
> and so cannot be mounted now.
> 
> REASON: Failed to create domain


The vbd issue wasn't that only one image could be loaded for one HVM
domain, if that's what you're saying. The issue was exceeding the number
of loopback devices on the system. Qemu-dm loads disk images using
loopback devices - so you are therefore the number of disk images able
to be mounted is limited to the number of configured loopback devices.

There was a bug in 11_create_concurrent_pos.py in xm-test because it
goes and creates as many concurrent domains as possible based on memory
and a cutoff of 50. This is fine for para virt, but broke for HVM
because of the loopback device limit. I have patched the test and it
should work for you. I have run 11_create_concurrent_pos.py on my x366
where I've changed the kernel option max_loop=256 and been able to load
50 disk images all using the same disk image. 

Thanks,

Dan