On Mon, Aug 07, 2023 at 03:41:21PM +0200, Peter Krempa wrote:
On Thu, Aug 03, 2023 at 09:48:01 +0200, Stefano Garzarella wrote:
On Wed, Aug 2, 2023 at 10:33 PM Jonathon Jongsma
<jjongsma@xxxxxxxxxx> wrote:
On 7/24/23 8:05 AM, Peter Krempa wrote:
[...]
>
> I've also noticed that using 'qcow2' format for the device
doesn't work:
>
> error: internal error: process exited while connecting to
monitor: 2023-07-24T12:54:15.818631Z qemu-system-x86_64:
-blockdev {"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":"libvirt-1-storage"}:
Could not read qcow2 header: Invalid argument
>
> If that is supposed to work, then qemu devs will probably
need to know
> about that, if that is not supposed to work, libvirt needs to add a
> check, because the error doesn't tell much. It's also possible I've
> messed up when formatting the image though, as didn't really try to
> figure out what's happening.
>
That's a good question, and I don't actually know the
answer. Were you
using an actual vdpa block device for your tests or were you
using the
vdpa block simulator kernel module? How did you set it up? Adding
Stefano to cc for his thoughts.
Yep, I would also like to understand how you initialized the device
with a qcow2 format.
Naively and originally I've simply used it as 'raw' at first and
formatted it from the guest OS. Then I've shut-down the VM and started
it back reconfiguring the image format as qcow2. This normally works
with real-file backed storage, and since the vdpa simulator seems to
persist the contents I supposed this would work.
Cool, I'll try that.
Can you try to reboot the VM, use it as `raw`, and read the qcow2 in the
vm from the guest OS?
Note: there could be some bugs in the simulator!
Theoretically, the best use case for vDPA block is that the backend
handles formats, for QEMU it should just be a virtio device, but being
a blockdev, we should be able to use formats anyway, so it should
work.
Yeah, ideally there will be no format driver in qemu used for these
devices (this is not yet the case, I'll need to fix libvirt to stop
using the 'raw' driver if not needed).
Here I'm more interested whether it is supposed to work, in which case
we want to allow using qcow2 as a format in libvirt, or it's not
supposed to work and we should forbid it before the user gets a
suboptimal error message such as now.
This is a good question. We certainly haven't tested it, because it's an
uncommon scenario, but as I said before, maybe it should work. I need to
check it better.
For now, waiting for real hardware, the only way to test vDPA block
support in QEMU is to use the simulator in the kernel or VDUSE.
With the kernel simulator we only have a 128 MB ramdisk available,
with VDUSE you can use QSD with any file:
$ modprobe -a vhost_vdpa vduse
$ qemu-storage-daemon \
--blockdev file,filename=/path/to/image.qcow2,cache.direct=on,aio=native,node-name=file
\
--blockdev qcow2,file=file,node-name=qcow2 \
--export vduse-blk,id=vduse0,name=vduse0,num-queues=1,node-name=qcow2,writable=on
$ vdpa dev add name vduse0 mgmtdev vduse
Then you have a /dev/vhost-vdpa-X device that you can use with the
`virtio-blk-vhost-vdpa` blockdev (note: vduse requires QEMU with a
memory-backed with `share=on`), but using raw since the qcow2 is
handled by QSD.
Of course, we should be able to use raw file with QSD and qcow2 on
qemu (although it's not the optimal configuration), but I don't know
how to initialize a `virtio-blk-vhost-vdpa` blockdev with a qcow2
image :-(
With the above qemu storage daemon you should be able to do that by
simply dropping the qcow2 format driver and simply exposing a qcow2
formatted image. It similarly works with NBD:
I've formatted 2 qcow2 images:
# qemu-img create -f qcow2 /root/image1.qcow2 100M
# qemu-img create -f qcow2 /root/image2.qcow2 100M
And then exported them both via vduse and nbd without interpreting
qcow2, thus making the QSD into just a dumb storage device:
# qemu-storage-daemon \
--blockdev file,filename=/root/image1.qcow2,cache.direct=on,aio=native,node-name=file1
\
--export vduse-blk,id=vduse0,name=vduse0,num-queues=1,node-name=file1,writable=on
\
--blockdev file,filename=/root/image2.qcow2,cache.direct=on,aio=native,node-name=file2
\
--nbd-server addr.type=unix,addr.path=/tmp/nbd.sock \
--export nbd,id=nbd0,node-name=file2,writable=on,name=exportname
Cool! Thanks for sharing!
Now when I start a VM using the NBD export in qcow2 format:
<disk type='network' device='disk'>
<driver name='qemu' type='qcow2'/>
<source protocol='nbd' name='exportname'>
<host transport='unix' socket='/tmp/nbd.sock'/>
</source>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x0'/>
</disk>
The VM starts fine, but when using:
<disk type='vhostvdpa' device='disk'>
<driver name='qemu' type='qcow2' cache='none'/>
<source dev='/dev/vhost-vdpa-0'/>
<target dev='vda' bus='virtio'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02'
function='0x0'/>
</disk>
I get:
error: internal error: QEMU unexpectedly closed the monitor
(vm='vdpa'): 2023-08-07T12:34:21.628520Z qemu-system-x86_64:
-blockdev {"node-name":"libvirt-1-format","read-only":false,"cache":{"direct":true,"no-flush":false},"driver":"qcow2","file":"libvirt-1-storage"}:
Could not read qcow2 header: Invalid argument
mmm, I just tried this scenario using QEMU directly and it worked.
These are the steps I did (qemu upstream,
commit 9400601a689a128c25fa9c21e932562e0eeb7a26):
./build/storage-daemon/qemu-storage-daemon \
--blockdev
file,filename=test.qcow2,cache.direct=on,aio=native,node-name=file
\
--export vduse-blk,id=vduse0,name=vduse0,num-queues=1,node-name=file,writable=on
vdpa dev add name vduse0 mgmtdev vduse
/build/qemu-system-x86_64 -m 512M -smp 2 \
-M q35,accel=kvm,memory-backend=mem \
-drive file=f38-vm-build.qcow2,format=qcow2,if=none,id=hd0 \
-device virtio-blk-pci,drive=hd0,bootindex=1 \
-blockdev node-name=drive_src1,driver=virtio-blk-vhost-vdpa,path=/dev/vhost-vdpa-0,cache.direct=on
\
-blockdev qcow2,node-name=qcow2,file=drive_src1 \
-device virtio-blk-pci,id=src1,bootindex=2,drive=qcow2 \
-object memory-backend-file,share=on,id=mem,size=512M,mem-path="/dev/hugepages"
Then I'm able to see /dev/vdb and /dev/vdb1.
(test.qcow2 has a fs on the first partition)
I mounted vdb1 and did I did md5sum on a file.
Then I turned off the machine, moved the `-blockdev qcow2...` from qemu
to QSD, and I did the same steps and checked that md5 is the same.
So it seems to work, but maybe we have something different.
My kernel host is: 6.4.7-200.fc38.x86_64
Thanks,
Stefano
