Discussion:
GUIX 0.7 under QEMU/KVM with virtio
(too old to reply)
Assaf Gordon
2014-10-04 04:59:54 UTC
Permalink
Hello Guix Developers,

I'm experimenting in using Guix under QEMU/KVM.

I've read these:
https://lists.gnu.org/archive/html/guix-devel/2014-09/msg00326.html
http://lists.gnu.org/archive/html/guix-devel/2014-09/msg00149.html

First,
I can provide another recipe:
## On Host
$ wget ftp://alpha.gnu.org/gnu/guix/gnu-usb-install-0.7.x86_64.xz
$ unxz gnu-usb-install-0.7.x86_64.xz
$ qemu-img create -q -f qcow2 guix.qcow2 5G
$ qemu-system-x86_64 --enable-kvm \
-m 1024 \
-net nic,model=virtio -net user \
-boot menu=on \
-hda gnu-usb-install-0.7.x86_64 \
-drive file=guix.qcow2,if=virtio,media=disk,index=0 \
-serial mon:stdio \
-vga std

## Inside guest:
1. Press F12 (quickly) for QEMU Boot menu
2. Choose "1" for QEMU ATA DISK 750MB SIZE (which is the USB image)
3. GRUB Loads, boots into Guix shell
4. The USB drive is "/dev/sda1"
5. The Disk image is "/dev/vda" (unpartitioned)
6. Parition with fdisk:
# fdisk /dev/vda
press n (new partition)
press p (primary partition)
(use defaults for all values)
a (activate parition)
1 (parition number)
w (write changes)
7. Create File system
# mkfs.ext4 -L guix /dev/vda1
8. Follow instructions at
http://www.gnu.org/software/guix/manual/html_node/System-Installation.html
# dhclient eth0
# mount /dev/vda1 /mnt
# deco start cow-store /mnt
# guix system init /mnt/etc/config.scm /mnt
(my 'config.scm' attached below)


Second,
I can confirm Nate's observation that using QEMU's "-usbdrive" option for the USB image causes everything to be VERY slow.
not sure why.
Using "-hda" for the USB image is much better.


Third,
After boot (before setup), I'm trying to get a login prompt on the serial port (which QEMU's redirect to the terminal).
I can do the following:
echo "hello" > /dev/ttyS0 => appears on the terminal

I can also boot with "console=ttyS0,9600n8" (in the GRUB command line), and the kernel messages appear on the console.
However, I can't get a login prompt on the serial console.

I tried variations of:
agetty -L 9600 ttyS0 linux

But they all exit after a timeout of few seconds, and no prompt appears on the serial console.
Any ideas ?


Fourth,
Sadly, after installation is complete, and after rebooting, the system fails to load from "/dev/vda1" (drops to "early boot guile").
Based on the kernel messages, it seems the "virtio_blk" driver is not loaded, and so "/dev/vda" is not available.
If I then switch QEMU parameters from "-drive if=virtio" to "-drive if=ide" the system loads fine (also requires changing grub's "--root" parameter).

Is there a way to fix this? force the kernel to load virto driver?




Regards,
- Assaf


=== config.scm, adapted for "/dev/vda" ====
(use-modules (gnu))

(operating-system
(host-name "guix07")
(timezone "Europe/Paris")
(locale "en_US.UTF-8")
(bootloader (grub-configuration (device "/dev/vda")))
(file-systems (cons (file-system
(device "/dev/vda1")
(mount-point "/")
(type "ext4"))
%base-file-systems))
(users (list (user-account
(name "miles")
(group "users")
(supplementary-groups '("wheel"))
(home-directory "/home/miles")))))
=================
Ludovic Courtès
2014-10-04 20:42:57 UTC
Permalink
Hi, Assaf,
Post by Assaf Gordon
First,
Thanks for the recipe. We should probably add a subsection on how to
install to a VM image in the manual. Would you like to amend guix.texi
for that?
Post by Assaf Gordon
Second,
I can confirm Nate's observation that using QEMU's "-usbdrive" option for the USB image causes everything to be VERY slow.
not sure why.
Using "-hda" for the USB image is much better.
Weird, no idea either.
Post by Assaf Gordon
Third,
After boot (before setup), I'm trying to get a login prompt on the serial port (which QEMU's redirect to the terminal).
echo "hello" > /dev/ttyS0 => appears on the terminal
I can also boot with "console=ttyS0,9600n8" (in the GRUB command line), and the kernel messages appear on the console.
However, I can't get a login prompt on the serial console.
agetty -L 9600 ttyS0 linux
But they all exit after a timeout of few seconds, and no prompt appears on the serial console.
Any ideas ?
I haven’t tried agetty, but it seems to have a hard-coded default login
program of “/bin/login”, which doesn’t exist here. Could you try
invoking it with -l $(guix build shadow)/bin/login ?

Alternately you could try adding a mingetty service to the
configuration:

(operating-system
...
(services (cons (mingetty-service "ttyS0")
%base-services)))
Post by Assaf Gordon
Fourth,
Sadly, after installation is complete, and after rebooting, the system fails to load from "/dev/vda1" (drops to "early boot guile").
Based on the kernel messages, it seems the "virtio_blk" driver is not loaded, and so "/dev/vda" is not available.
If I then switch QEMU parameters from "-drive if=virtio" to "-drive if=ide" the system loads fine (also requires changing grub's "--root" parameter).
Is there a way to fix this? force the kernel to load virto driver?
Currently all the drivers needed to mount the root partition must be
explicitly loaded in the initrd. So yes, you would need to have the
virtio modules loaded from the initrd (info "(guix) Initial RAM Disk"):

(operating-system
...
(initrd (lambda (file-systems . rest)
(apply base-initrd file-systems
#:extra-modules '("virtio.ko" "virtio_ring.ko"
"virtio_blk.ko")
rest))))

I think this should work.

Thanks for your feedback!

Ludo’.
Assaf Gordon
2014-10-05 00:15:55 UTC
Permalink
Hi,

Thanks for the help.
Post by Ludovic Courtès
Post by Assaf Gordon
Is there a way to fix this? force the kernel to load virto driver?
Currently all the drivers needed to mount the root partition must be
explicitly loaded in the initrd. So yes, you would need to have the
(operating-system
...
(initrd (lambda (file-systems . rest)
(apply base-initrd file-systems
#:extra-modules '("virtio.ko" "virtio_ring.ko"
"virtio_blk.ko")
rest))))
Two more things were needed:
1. adding"virtio_pci.ko" and "virtio_net.ko" to the list of drivers.
2. Labeling "/dev/vda1" as "gnu-disk-image" (when doing "mkfs.ext4 -L").
This wasn't needed to boot from "/dev/sda1", but was needed to use "/dev/vda1".
Perhaps some hard-coded thing ?

With these, the VM boots with virtio disk and network.
Post by Ludovic Courtès
Post by Assaf Gordon
After boot (before setup), I'm trying to get a login prompt on the serial port (which QEMU's redirect to the terminal).
echo "hello" > /dev/ttyS0 => appears on the terminal
I can also boot with "console=ttyS0,9600n8" (in the GRUB command line), and the kernel messages appear on the console.
However, I can't get a login prompt on the serial console.
agetty -L 9600 ttyS0 linux
But they all exit after a timeout of few seconds, and no prompt appears on the serial console.
Any ideas ?
I haven’t tried agetty, but it seems to have a hard-coded default login
program of “/bin/login”, which doesn’t exist here. Could you try
invoking it with -l $(guix build shadow)/bin/login ?
Alternately you could try adding a mingetty service to the
(operating-system
...
(services (cons (mingetty-service "ttyS0")
%base-services)))
I still can't get serial console to work, perhaps needs more fidgeting.
Trying "mingetty ttyS0" from the command line fails with:
ttyS0: no controlling tty: Operation not permitted
So I'm not sure 'mingetty' is the way to go.

I'm not well-versed in scheme, so it will take me some more time to figure things out...

-Assaf
Ludovic Courtès
2014-10-05 12:29:12 UTC
Permalink
Post by Assaf Gordon
Post by Ludovic Courtès
Post by Assaf Gordon
Is there a way to fix this? force the kernel to load virto driver?
Currently all the drivers needed to mount the root partition must be
explicitly loaded in the initrd. So yes, you would need to have the
(operating-system
...
(initrd (lambda (file-systems . rest)
(apply base-initrd file-systems
#:extra-modules '("virtio.ko" "virtio_ring.ko"
"virtio_blk.ko")
rest))))
1. adding"virtio_pci.ko" and "virtio_net.ko" to the list of drivers.
OK.
Post by Assaf Gordon
2. Labeling "/dev/vda1" as "gnu-disk-image" (when doing "mkfs.ext4 -L").
This wasn't needed to boot from "/dev/sda1", but was needed to use "/dev/vda1".
Perhaps some hard-coded thing ?
“gnu-disk-image” is the label of the root partition of the USB
installation image (see gnu/system/install.scm.)

However, the user’s root can carry any label, as long as the
corresponding ‘file-system’ declaration uses it.
Post by Assaf Gordon
With these, the VM boots with virtio disk and network.
Good.
Post by Assaf Gordon
Post by Ludovic Courtès
I haven’t tried agetty, but it seems to have a hard-coded default login
program of “/bin/login”, which doesn’t exist here. Could you try
invoking it with -l $(guix build shadow)/bin/login ?
Alternately you could try adding a mingetty service to the
(operating-system
...
(services (cons (mingetty-service "ttyS0")
%base-services)))
I still can't get serial console to work, perhaps needs more fidgeting.
Did you try agetty with -l as suggested above?
Post by Assaf Gordon
ttyS0: no controlling tty: Operation not permitted
Is mingetty running as root here? If it is, could you strace it to see
exactly what returns EPERM?

HTH,
Ludo’.
Assaf Gordon
2014-10-05 23:29:16 UTC
Permalink
Hello,
Post by Ludovic Courtès
Post by Assaf Gordon
Post by Ludovic Courtès
I haven’t tried agetty, but it seems to have a hard-coded default login
program of “/bin/login”, which doesn’t exist here. Could you try
invoking it with -l $(guix build shadow)/bin/login ?
Alternately you could try adding a mingetty service to the
(operating-system
...
(services (cons (mingetty-service "ttyS0")
%base-services)))
I still can't get serial console to work, perhaps needs more fidgeting.
Did you try agetty with -l as suggested above?
Yes. Same as before - it exists after a timeout of few seconds.
Post by Ludovic Courtès
Post by Assaf Gordon
ttyS0: no controlling tty: Operation not permitted
Is mingetty running as root here? If it is, could you strace it to see
exactly what returns EPERM?
Yes. Running as root.

I don't have "strace" installed - how do I install it ? (I'm very new to guix).

Thanks,
- Assaf
Ludovic Courtès
2014-10-06 19:28:44 UTC
Permalink
Post by Assaf Gordon
Post by Ludovic Courtès
Post by Assaf Gordon
Post by Ludovic Courtès
I haven’t tried agetty, but it seems to have a hard-coded default login
program of “/bin/login”, which doesn’t exist here. Could you try
invoking it with -l $(guix build shadow)/bin/login ?
Alternately you could try adding a mingetty service to the
(operating-system
...
(services (cons (mingetty-service "ttyS0")
%base-services)))
I still can't get serial console to work, perhaps needs more fidgeting.
Did you try agetty with -l as suggested above?
Yes. Same as before - it exists after a timeout of few seconds.
Post by Ludovic Courtès
Post by Assaf Gordon
ttyS0: no controlling tty: Operation not permitted
Is mingetty running as root here? If it is, could you strace it to see
exactly what returns EPERM?
Yes. Running as root.
I don't have "strace" installed - how do I install it ? (I'm very new to guix).
Run ‘guix package -i strace’. Preferably register hydra.gnu.org.pub to
enable “substitutes” before doing that, so the system doesn’t end up
building the world (info "(guix) Substitutes").

HTH,
Ludo’.

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