doc: update docs in ociTools, follow doc conventions

doc/build-helpers/images/ocitools.section.md

@@ -1,37 +1,104 @@
 # pkgs.ociTools {#sec-pkgs-ociTools}
 
-`pkgs.ociTools` is a set of functions for creating containers according to the [OCI container specification v1.0.0](https://github.com/opencontainers/runtime-spec). Beyond that, it makes no assumptions about the container runner you choose to use to run the created container.
+`pkgs.ociTools` is a set of functions for creating runtime container bundles according to the [OCI runtime specification v1.0.0](https://github.com/opencontainers/runtime-spec/blob/v1.0.0/spec.md).
+It makes no assumptions about the container runner you choose to use to run the created container.
+
+The set of functions in `pkgs.ociTools` currently does not handle the [OCI image specification](https://github.com/opencontainers/image-spec).
+
+At a high-level an OCI implementation would download an OCI Image then unpack that image into an OCI Runtime filesystem bundle.
+At this point the OCI Runtime Bundle would be run by an OCI Runtime.
+`pkgs.ociTools` provides utilities to create OCI Runtime bundles.
 
 ## buildContainer {#ssec-pkgs-ociTools-buildContainer}
 
-This function creates a simple OCI container that runs a single command inside of it. An OCI container consists of a `config.json` and a rootfs directory. The nix store of the container will contain all referenced dependencies of the given command.
+This function creates an OCI runtime container (consisting of a `config.json` and a root filesystem directory) that runs a single command inside of it.
+The nix store of the container will contain all referenced dependencies of the given command.
+
+This function has an assumption that the container will run on POSIX platforms, and sets configurations (such as the user running the process or certain mounts) according to this assumption.
+Because of this, a container built with `buildContainer` will not work on Windows or other non-POSIX platforms without modifications to the container configuration.
+These modifications aren't supported by `buildContainer`.
+
+For `linux` platforms, `buildContainer` also configures the following namespaces (see {manpage}`unshare(1)`) to isolate the OCI container from the global namespace:
+PID, network, mount, IPC, and UTS.
+
+Note that no user namespace is created, which means that you won't be able to run the container unless you are the `root` user.
+
+### Inputs {#ssec-pkgs-ociTools-buildContainer-inputs}
+
+`buildContainer` expects an argument with the following attributes:
+
+`args` (List of String)
+
+: Specifies a set of arguments to run inside the container.
+  Any packages referenced by `args` will be made available inside the container.
+
+`mounts` (Attribute Set; _optional_)
+
+: Would specify additional mounts that the runtime must make available to the container.
+
+  :::{.warning}
+  As explained in [issue #290879](https://github.com/NixOS/nixpkgs/issues/290879), this attribute is currently ignored.
+  :::
+
+  :::{.note}
+  `buildContainer` includes a minimal set of necessary filesystems to be mounted into the container, and this set can't be changed with the `mounts` attribute.
+  :::
+
+  _Default value:_ `{}`.
 
-The parameters of `buildContainer` with an example value are described below:
+`readonly` (Boolean; _optional_)
+
+: If `true`, sets the container's root filesystem as read-only.
+
+  _Default value:_ `false`.
+
+`os` **DEPRECATED**
+
+: Specifies the operating system on which the container filesystem is based on.
+  If specified, its value should follow the [OCI Image Configuration Specification](https://github.com/opencontainers/image-spec/blob/main/config.md#properties).
+  According to the linked specification, all possible values for `$GOOS` in [the Go docs](https://go.dev/doc/install/source#environment) should be valid, but will commonly be one of `darwin` or `linux`.
+
+  _Default value:_ `"linux"`.
+
+`arch` **DEPRECATED**
+
+: Used to specify the architecture for which the binaries in the container filesystem have been compiled.
+  If specified, its value should follow the [OCI Image Configuration Specification](https://github.com/opencontainers/image-spec/blob/main/config.md#properties).
+  According to the linked specification, all possible values for `$GOARCH` in [the Go docs](https://go.dev/doc/install/source#environment) should be valid, but will commonly be one of `386`, `amd64`, `arm`, or `arm64`.
+
+  _Default value:_ `x86_64`.
+
+### Examples {#ssec-pkgs-ociTools-buildContainer-examples}
+
+::: {.example #ex-ociTools-buildContainer-bash}
+# Creating an OCI runtime container that runs `bash`
+
+This example uses `ociTools.buildContainer` to create a simple container that runs `bash`.
 
 ```nix
-buildContainer {
+{ ociTools, lib, bash }:
+ociTools.buildContainer {
   args = [
-    (with pkgs;
-      writeScript "run.sh" ''
-        #!${bash}/bin/bash
-        exec ${bash}/bin/bash
-      '').outPath
+    (lib.getExe bash)
   ];
 
-  mounts = {
-    "/data" = {
-      type = "none";
-      source = "/var/lib/mydata";
-      options = [ "bind" ];
-    };
-  };
-
   readonly = false;
 }
 ```
 
-- `args` specifies a set of arguments to run inside the container. This is the only required argument for `buildContainer`. All referenced packages inside the derivation will be made available inside the container.
+As an example of how to run the container generated by this package, we'll use `runc` to start the container.
+Any other tool that supports OCI containers could be used instead.
 
-- `mounts` specifies additional mount points chosen by the user. By default only a minimal set of necessary filesystems are mounted into the container (e.g procfs, cgroupfs)
+```shell
+$ nix-build
+(some output removed for clarity)
+/nix/store/7f9hgx0arvhzp2a3qphp28rxbn748l25-join
 
-- `readonly` makes the container's rootfs read-only if it is set to true. The default value is false `false`.
+$ cd /nix/store/7f9hgx0arvhzp2a3qphp28rxbn748l25-join
+$ nix-shell -p runc
+[nix-shell:/nix/store/7f9hgx0arvhzp2a3qphp28rxbn748l25-join]$ sudo runc run ocitools-example
+help
+GNU bash, version 5.2.26(1)-release (x86_64-pc-linux-gnu)
+(some output removed for clarity)
+```
+:::

doc/manpage-urls.json

@@ -318,5 +318,6 @@
   "passwd(5)": "https://man.archlinux.org/man/passwd.5",
   "group(5)": "https://man.archlinux.org/man/group.5",
   "login.defs(5)": "https://man.archlinux.org/man/login.defs.5",
+  "unshare(1)": "https://man.archlinux.org/man/unshare.1.en",
   "nix-shell(1)": "https://nixos.org/manual/nix/stable/command-ref/nix-shell.html"
 }