Unable to mount root in Hyper-V VM

[Kichileung]

As per Reddit: https://www.reddit.com/r/Gentoo/comments/1m07nt2/hyperv_vm_systemdboot_gentookernelbin_ugrd_unable/

I am unable to mount root using a initrd made by ugrd in Hyper-V virtual machine, using the stock gentoo-kernel / gentoo-kernel-bin.
Only when I use a "localyesconfig" config that builds all used modules statically then I can mount root.

Reproduced with ugrd 2.0.1 and with -9999.

Attached screenshot of the bootup and output of emerge --config gentoo-kernel.

emerge-config-gentoo-kernel.log

[Kichileung]

lsmod from Gentoo installCD outside of chroot.

lsmod.txt

[desultory]

hmm it seems to be pulling "sd_mod" for the storage driver. After you press space, does it show loaded kernel modules and block devices?

that module is builtin so it's esseentially ignored. I wonder if another driver is required for hyper-v?

DEBUG    | ugrd.InitramfsGenerator                    | [sd_mod] Module info: {'filename': '(builtin)'}

maybe "hv_vmbus"?

if you try to build with "--lsmod" or specify kmods in the "kmod_init" config in /etc/ugrd/config.toml that may help figure out which module is required.

like:

kmod_init = ["hv_vmbus"]

[Kichileung]

Finally! kmod_init = [ "hv_storvsc" ] did the trick.

I saw lsmod based detection is disabled by default but maybe an exception could be made for this hv_storvsc module?

[desultory]

Finally! kmod_init = [ "hv_storvsc" ] did the trick.

I saw lsmod based detection is disabled by default but maybe an exception could be made for this hv_storvsc module?

the lsmod detection is meant to be more of a last resort, kinda "yolo, try to get anything and everything, if it's not masked"

Unless we can figure out a way to "trace" that his kmod is being used, like some info in /sys or /proc for example, I think it would be best to simply always check if that module is loaded, and try to use it. Something better would be some kind of simple platform detection to see it's in a hyper-v vm, and include necessary modules. That should cover the case of building on a system without modules for a new kernel with modules.

Maybe there is some info around /sys/class/block/sda/?

Some file in /sys/class/dmi/id may indicate that it's a hyper v vm as well

[Kichileung]

Hmm, I hope the below helps. Stuff from sysfs

livecd /mnt/gentoo # cat /sys/class/block/sda/device/model
Virtual Disk
livecd /mnt/gentoo # cat /sys/class/block/sda/device/modalias
scsi:t-0x00
livecd /mnt/gentoo # cat /sys/class/block/sda/device/vendor
Msft
livecd /mnt/gentoo # cat /sys/class/dmi/id/sys_vendor
Microsoft Corporation
livecd /mnt/gentoo # cat /sys/class/dmi/id/product_name
Virtual Machine

[desultory]

thanks, I can use some of that info to start making a module to autodetect this stuff :D

[desultory]

would you mind trying the latest git release (9999 on gentoo)?

I think this patch may fix the autodetction issues you're facing (and fixes some others another user pointed out): #337

[Kichileung]

It is still failing with latest -9999 from git, cannot find root device, just as before. I spun up a new VM just to test so it's not polluted by earlier git code :)

This is the latest emerge --config gentoo-kernel output.

emerge-config-gentoo-kernel.txt

[desultory]

It is still failing with latest -9999 from git, cannot find root device, just as before. I spun up a new VM just to test so it's not polluted by earlier git code :)

This is the latest emerge --config gentoo-kernel output.

emerge-config-gentoo-kernel.txt

ah i forgot to make it actually add those kmods lol, easy fix

[desultory]

I think this should fix it

#338

[Kichileung]

Now ugRD detects virtio_blk kmod as necessary but then later on removes it and this causes a critical error.

Please see latest "emerge linux-firmware" output which fails in initrd building stage.

filtered.log

[desultory]

is that kernel module missing?

DEBUG    | ugrd.InitramfsGenerator                    | [virtio_blk] Modinfo command: modinfo virtio_blk --set-version 6.12.38
ERROR    | ugrd.InitramfsGenerator                    | [virtio_blk] Failed to get modinfo for init kernel module: [virtio_blk] Modinfo returned no output.
DEBUG    | ugrd.InitramfsGenerator                    | [virtio_blk] Failed to get modinfo for kernel module: [virtio_blk] Modinfo returned no output.

[desultory]

#339

this should make it so "vendor" modules are required, but "product" ones are optional.

Generally, virtio_blk is included in dist-kernel though?

[Kichileung]

is that kernel module missing?

DEBUG    | ugrd.InitramfsGenerator                    | [virtio_blk] Modinfo command: modinfo virtio_blk --set-version 6.12.38
ERROR    | ugrd.InitramfsGenerator                    | [virtio_blk] Failed to get modinfo for init kernel module: [virtio_blk] Modinfo returned no output.
DEBUG    | ugrd.InitramfsGenerator                    | [virtio_blk] Failed to get modinfo for kernel module: [virtio_blk] Modinfo returned no output.

Yes, not in the lsmod output, booted into livecd

livecd ~ # lsmod | grep virt
livecd ~ #

[Kichileung]

Generally, virtio_blk is included in dist-kernel though?

Yes on Gentoo install cd

livecd ~ # zgrep VIRTIO_BLK /proc/config.gz
CONFIG_VIRTIO_BLK=m