snap-bootstrap: add scan-disk subcommand

[valentindavid]

This command is expected to be called from udev. This creates symlinks /dev/ubuntu/ubuntu-{seed,boot,data,save}.

Then we can bind snap-bootstrap initramfs-mounts to dev-ubuntu-ubuntu-seed.device.

[valentindavid]

This works with snapcore/core-initrd#107

[valentindavid]

Would it be possible to get the same information just by running blkid instead of using the library?

We cannot list partitions from blkid.

[xnox]

Given SEED is ESP; and we bind the initramfs-mounts unit to the SEED; i am wondering if we can instead turn on / patch the systemd's gpt-auto-generator which can create esp mount in /efi and use that instead?

Looking more at this, I actually don't quite like the behaviour of gpt-auto-generator. Because the good bits of it are not what we need here.

Ideally we would only read efi_loader_get_device_part_uuid (aka LoaderDevicePartUUID) and generate .device unit for it, and bind initramfs-mounts service unit to it. Before any drives appear.

Thus without waiting udev to exec scan-disk to process them all either.

[valentindavid]

Ideally we would only read efi_loader_get_device_part_uuid (aka LoaderDevicePartUUID) and generate .device unit for it, and bind initramfs-mounts service unit to it. Before any drives appear.

Thus without waiting udev to exec scan-disk to process them all either.

So almost what I have done, but a symlink on the whole disk rather than the partitions?

[pedronis]

@valentindavid can the description or some comment in the code include the actual udev rules that this will be used from? it's a bit unclear just from the code how things go from the code in scan-disk to have /dev/ubuntu/disk symlinked?

What's the plan for testing the cmd_scan_disk code?

[valentindavid]

@valentindavid can the description or some comment in the code include the actual udev rules that this will be used from? it's a bit unclear just from the code how things go from the code in scan-disk to have /dev/ubuntu/disk symlinked?

Sure. We could even add the rules to snapd and install them into core-initrd.

What's the plan for testing the cmd_scan_disk code?

I think I will need to mock libblkid somehow to test it.

Loop devices need root to be setup, and I do not think there is as this point any nice user land block devices. I think only character devices can be emulated with CUSE. Not block.

[valentindavid]

What's the plan for testing the cmd_scan_disk code?

I have added tests.

I still have to add tests for the changes in cmd_initramfs_mounts.go (when /dev/ubuntu/disk exists). But that should be straight forward.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 62.35294% with 96 lines in your changes are missing coverage. Please review.

Project coverage is 78.84%. Comparing base (f7fea7f) to head (6ee943e). Report is 44 commits behind head on master.

Files	Patch %	Lines
cmd/snap-bootstrap/cmd_scan_disk.go	68.42%	46 Missing and 20 partials :warning:
osutil/disks/disks_linux.go	0.00%	12 Missing :warning:
osutil/disks/mockdisk.go	0.00%	12 Missing :warning:
cmd/snap-bootstrap/cmd_initramfs_mounts.go	72.72%	4 Missing and 2 partials :warning:

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Additional details and impacted files

@@            Coverage Diff             @@
##           master   #12006      +/-   ##
==========================================
- Coverage   78.88%   78.84%   -0.04%     
==========================================
  Files        1037     1039       +2     
  Lines      132881   133744     +863     
==========================================
+ Hits       104817   105454     +637     
- Misses      21523    21692     +169     
- Partials     6541     6598      +57     

Flag	Coverage Δ
unittests	78.84% <62.35%> (-0.04%)	:arrow_down:

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