lib/ukzeropage: Introduce zeropage library

[andreittr]

Description of changes

This change introduces ukzeropage, a library providing a singleton instance of read-only page filled with zero bytes. This page exists independent of virtual memory support.

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran the checkpatch.uk on your commit series before opening this PR;
• Updated relevant documentation.

Base target

• Architecture(s): [e.g. x86_64 or N/A]
• Platform(s): [e.g. kvm, xen or N/A]
• Application(s): [e.g. app-python3 or N/A]

Additional configuration

N/A

[eduardvintila]

All good.

Reviewed-by: Eduard Vintilă eduard.vintila47@gmail.com

[mogasergiu]

Is there a specific use-case for this addition as of now? I understand this is part of more work to come, but I would like to wait and see how that makes use of this before merging this. Therefore, I propose we move this PR to 0.18.

[andreittr]

Is there a specific use-case for this addition as of now? I understand this is part of more work to come, but I would like to wait and see how that makes use of this before merging this. Therefore, I propose we move this PR to 0.18.

In addition to work in progress (that is not targeted for 0.17), this change is intended to be used together with #1226 and #1411 to provide sendfile support for zerofiles (sendfile is blocked pending the above 2 PRs). Depending on whether we want ukfile sendfile support in 0.17 or not we can decide to postpone this.

[mogasergiu]

Ah I see. Yep, I would rather we reviewed that first to see how this is actually used before merging something unused.