Colin Walters cgwalters

In Rust, the Option and Result types are really common. Here are a few idioms I've discovered for working with them using combinators which can simplify code:

map(Ok).unwrap_or_else(): Taking Option with fallible fallback to T

    // Our program needs a string for something (e.g. filename, database table name, etc).
    // To start, we can get this as an optional string - here a CLI argument, but it could be anything; e.g.
    // a value parsed from JSON, etc.  The `.nth(1)` call here gives us an `Option<String>`.
    // We want to compute a fallback value, but doing so can fail (e.g. return `Result<String>`).

Ubuntu Core investigation

Following up to this tweet.

Setup

I followed the qemu instructions, using ubuntu-core-20-amd64.img.

Investigating the mount/block setup

$ podman pull quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:502f9b8333a88ecee1eb7e904af5cb0c75946e3084a553374079abf862446c70
Trying to pull quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:502f9b8333a88ecee1eb7e904af5cb0c75946e3084a553374079abf862446c70...
Getting image source signatures
Copying blob 1e138cc587ef done  
Copying blob 54183f4a5679 done  
Copying blob fadcf7c660d5 done  
Copying config 10b43b2460 done  
Writing manifest to image destination
Storing signatures

flowchart TB
    subgraph ostreebuild [ostree build]
    quayprevious["previous ostree container"] -->|change detection| container["ostree container"]
    configgit["config git"]-->container
    rpms --> container["ostree container"]
    container --> quay["quay.io"]
    end
    subgraph imagebuild [image build]
 quay --&gt; qemu["qemu image"]

$ rpm -q gcc cargo
gcc-8.5.0-7.el8.x86_64
cargo-1.56.1-2.module+el8.6.0+13527+64f2eba2.x86_64
$ rhpkg local
...
error: build-id found in /var/home/walters/rpmbuild/BUILDROOT/rpm-ostree-2021.14-2.el8.x86_64/usr/bin/rpm-ostree too small
error: Generating build-id links failed

walters@quicksilver ~> podman run --rm -ti quay.io/cgwalters/fcos bash
# rpm -Uvh https://kojipkgs.fedoraproject.org//packages/libdnf/0.64.0/1.fc35/x86_64/libdnf-0.64.0-1.fc35.x86_64.rpm https://kojipkgs.fedoraproject.org//packages/microdnf/3.8.0/2.fc35/x86_64/microdnf-3.8.0-2.fc35.x86_64.rpm https://kojipkgs.fedoraproject.org//packages/dnf/4.9.0/1.fc35/noarch/dnf-data-4.9.0-1.fc35.noarch.rpm https://kojipkgs.fedoraproject.org//packages/libpeas/1.30.0/5.fc35/x86_64/libpeas-1.30.0-5.fc35.x86_64.rpm https://kojipkgs.fedoraproject.org//packages/gobject-introspection/1.70.0/1.fc35/x86_64/gobject-introspection-1.70.0-1.fc35.x86_64.rpm
Retrieving https://kojipkgs.fedoraproject.org//packages/libdnf/0.64.0/1.fc35/x86_64/libdnf-0.64.0-1.fc35.x86_64.rpm
Retrieving https://kojipkgs.fedoraproject.org//packages/microdnf/3.8.0/2.fc35/x86_64/microdnf-3.8.0-2.fc35.x86_64.rpm
Retrieving https://kojipkgs.fedoraproject.org//packages/dnf/4.9.0/1.fc35/noarch/dnf-data-4.9.0-1.fc35.noarch.rpm
Retrieving https://kojipkgs.fedorap

	```
	-rw-r--r--. 1 walters walters 613M Feb 15 17:16 qcow2.xz
	-rw-r--r--. 1 walters walters 669M Feb 15 17:58 qcow2.zstd
	$ time xz -d < qcow2.xz >/dev/null

	________________________________________________________
	Executed in 12.62 secs fish external
	usr time 12.51 secs 190.00 micros 12.51 secs
	sys time 0.09 secs 69.00 micros 0.09 secs

	#![feature(try_trait_v2)]

	use anyhow::Result; // 1.0.57
	use core::ops::Try;

	trait TryOrElse<T> {
	fn try_or_else<R: Try<Output = T>, F: FnOnce() -> R>(self, f: F) -> R;
	}

	// Proposed new API for Option https://github.com/rust-lang/libs-team/issues/59

	```
	$ cosa generate-release-meta --stream-name podman --stream-baseurl https://fedorapeople.org/groups/podman --url https://fedorapeople.org/groups/podman/builds/35.20220208.dev.0/x86_64/meta.json --output stream.json
	Downloading https://fedorapeople.org/groups/podman/builds/35.20220208.dev.0/x86_64/meta.json...
	podman stream
	x86_64 images:
	- qemu
	Successfully wrote release file at stream.json
	$ jq . < stream.json
	{
	"release": "35.20220208.dev.0",

	```
	walters@toolbox /v/s/w/b/rhcos-master> oc image info (oc adm release info --image-for=machine-os-content quay.io/openshift-release-dev/ocp-release:4.6.52-x86_64)
	Name: quay.io/openshift-release-dev/ocp-v4.0-art-dev@sha256:6ea6c6f23e0fe047c5813c0607c3bed53dc6bcf2c1064f8fc72235236aacc182
	Media Type: application/vnd.docker.distribution.manifest.v2+json
	Created: 39d ago
	Image Size: 1.001GB in 3 layers
	Layers: 86.08MB sha256:c2aecb3e557dba3008677634224d2eec02c1ccdf36e29026d57e933095a790a6
	1.883kB sha256:65b3ce9d57bf94cef9ca928be2f78a5f61be880670860dbd05111489cac97368
	914.5MB sha256:322dbbe859bd09590f8612b9ae0b59a2cc9d4f869c310a4525c86f7d36d7a614
	OS: linux