Only run udevadm if it exists

[oittaa]

For example OpenWRT doesn't have udevadm. This tool works perfectly otherwise, but it prints and an error message, when it tries to execute udevadm.

[dermotbradley]

Hi. I was intending to submit a MR to address this and also a similar change to mount-image-callback, both of which I have been using on Alpine Linux for a while, once #35 was merged.

So how do you want to handle this? Go with this MR and I raise a MR for mount-image-callback? Or you close this and I submit a single MR for both growpart and mount-image-callback?

BTW I also have another MR yet to submit for patches (that again I've been using for months with Alpine Linux) for Busybox compatibility in cloud-localds, mount-image-callback, and resize-part-image.

[oittaa]

Well, to me it's fine either way. But since this pull request is already here, maybe you could just make a pull request for mount-image-callback?

[dermotbradley]

But since this pull request is already here, maybe you could just make a pull request for mount-image-callback?

Ok, then I'd suggest you modify the comment on line 176 to add "(if installed)" after "run udevadm settle".

[dermotbradley]

Congrats, now it looks exactly like the patch I've been using for some time: https://git.alpinelinux.org/aports/tree/community/cloud-utils/02-make-udev-optional.patch :-)

[paride]

Hi @oittaa and thanks for this PR. The change itself LGTM, but I wonder how safe it is. It's probably safe to assume that when udevadm is not available the system is not using udev, so we don't need to settle it, and we leave the burden of making sure that the kernel events have been processed to whatever tooling is calling growpart on non-udev/non-systemd systems. Is my understanding correct here?

It would be nice to run CI on Alpine, but that's not supported by GitHub Actions (https://github.com/actions/virtual-environments).

[oittaa]

Is my understanding correct here?

Correct.

It would be nice to run CI on Alpine, but that's not supported by GitHub Actions (https://github.com/actions/virtual-environments).

A workaround could be to run in an Alpine Linux docker container?

[dermotbradley]

I wonder how safe it is. It's probably safe to assume that when udevadm is not available the system is not using udev, so we don't need to settle it, and we leave the burden of making sure that the kernel events have been processed to whatever tooling is calling growpart on non-udev/non-systemd systems. Is my understanding correct here?

Hi. I applied basically the same change to the Alpine packaged cloud-utils (which I'm the maintainer of) back in Nov 2020.

I have tested Alpine VMs using mdev, rather than eudev/udev, with such a patched growpart via a 1st-time boot init.d script and have not encountered any issues.

[paride]

This LGTM, thanks!