Updates to the docs

Some of this was out of date or missing.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

docs/yaml.md

@@ -1,25 +1,33 @@
 # Configuration Reference
 
-The yaml configuration specifies the components and the build time artifacts. All components
+The `moby` tool assembles a set of containerised components into in image. The simplest
+type of image is just a `tar` file of the contents (useful for debugging) but more useful
+outputs add a `Dockerfile` to build a container, or build a full disk image that can be
+booted as a linuxKit VM. The main use case is to build an assembly that includes
+`containerd` to run a set of containers, but the tooling is very generic.
+
+The yaml configuration specifies the components used to build up an image . All components
 are downloaded at build time to create an image. The image is self-contained and immutable,
 so it can be tested reliably for continuous delivery.
 
 The configuration file is processed in the order `kernel`, `init`, `onboot`, `services`, `files`.
-Each section adds file to the root file system
+Each section adds file to the root file system. Sections may be omitted.
 
 ## `kernel`
 
+The `kernel` section is only required if booting a VM. The files will be put into the `boot/`
+directory, where they are used to build bootable images.
+
 The `kernel` section defines the kernel configuration. The `image` field specifies the Docker image,
-which should contain a `bzImage` (for `amd64` architecture, others may vary) and a file
+which should contain a `kernel` file that will be booted (eg a `bzImage` for `amd64`) and a file
 called `kernel.tar` which is a tarball that is unpacked into the root, which should usually
-contain a kernel modules directory. See [`kernel/`](../kernel/) for source code. `cmdline`
-specifies the kernel command line options if required.
+contain a kernel modules directory. `cmdline` specifies the kernel command line options if required.
 
 ## `init`
 
 The `init` section is a list of images that are used for the `init` system and are unpacked directly
 into the root filesystem. This should bring up `containerd`, start the system and daemon containers,
-and set up basic filesystem mounts. See [`pkg/init/`](../pkg/init/) for source code. For ease of
+and set up basic filesystem mounts. in the case of a LinuxKit system. For ease of
 modification `runc` and `containerd` images, which just contain these programs are added here
 rather than bundled into the `init` container.
 
@@ -37,17 +45,38 @@ run with `containerd`.  Startup order is undefined, so containers should wait
 on any resources, such as networking, that they need.  See [Image
 specification](#image-specification) for a list of supported fields.
 
+## `files`
+
+The files section can be used to add files inline in the config, or from an external file.
+
+```
+files:
+  - path: dir
+    directory: true
+    mode: "0777"
+  - path: dir/name1
+    source: "/some/path/on/local/filesystem"
+    mode: "0666"
+  - path: dir/name2
+    contents: "orange"
+    mode: "0644"
+```
+
+Specifying the `mode` is optional, and will default to `0600`. Leading directories will be
+created if not specified.
+
 ## `trust`
 
 The `trust` section specifies which build components are to be cryptographically verified with
 [Docker Content Trust](https://docs.docker.com/engine/security/trust/content_trust/) prior to pulling.
 Trust is a central concern in any build system, and LinuxKit's is no exception: Docker Content Trust provides authenticity,
 integrity, and freshness guarantees for the components it verifies.  The LinuxKit maintainers are responsible for signing
-`mobylinux` components, though collaborators can sign their own images with Docker Content Trust or [Notary](https://github.com/docker/notary).
+`linuxkit` components, though collaborators can sign their own images with Docker Content Trust or [Notary](https://github.com/docker/notary).
 
 - `image` lists which individual images to enforce pulling with Docker Content Trust.
 The image name may include tag or digest, but the matching also succeeds if the base image name is the same.
-- `org` lists which organizations for which Docker Content Trust is to be enforced across all images (ex: `mobylinux` is the org for `mobylinux/kernel`)
+- `org` lists which organizations for which Docker Content Trust is to be enforced across all images,
+for example `linuxkit` is the org for `linuxkit/kernel`
 
 ## Image specification
 
@@ -55,6 +84,17 @@ Entries in the `onboot` and `services` sections specify an OCI image and
 options. Default values may be specified using the `org.mobyproject.config` image label.
 For more details see the [OCI specification](https://github.com/opencontainers/runtime-spec/blob/master/spec.md).
 
+If the `org.mobylinux.config` label is set in the image, that specifies default values for these fields if they
+are not set in the yaml file. You can override the label by setting the value, or setting it to be empty to remove
+the specification for that value in the label.
+
+If you need an OCI option that is not specified here please open an issue or pull request as the list is not yet
+complete.
+
+By default the containers will be run in the host `net`, `ipc` and `uts` namespaces, as that is the usual requirement;
+in many ways they behave like pods in Kubernetes. Mount points must already exist, as must a file or directory being
+bind mounted into a container.
+
 - `name` a unique name for the program being executed, used as the `containerd` id.
 - `image` the Docker image to use for the root filesystem. The default command, path and environment are
   extracted from this so they need not be filled in.
@@ -68,12 +108,12 @@ For more details see the [OCI specification](https://github.com/opencontainers/r
   similar to the `-v` option for bind mounts in Docker.
 - `tmpfs` is a simpler interface to mount a `tmpfs`, like `--tmpfs` in Docker, taking `/dest:opt1,opt2`.
 - `command` will override the command and entrypoint in the image with a new list of commands.
-- `env` will override the environment in the image with a new environment list
+- `env` will override the environment in the image with a new environment list. Specify variables as `VAR=value`.
 - `cwd` will set the working directory, defaults to `/`.
-- `net` sets the network namespace, either to a path, or if `host` is specified it will use the host namespace.
+- `net` sets the network namespace, either to a path, or if `none` or `new` is specified it will use a new namespace.
+- `ipc` sets the ipc namespace, either to a path, or if `new` is specified it will use a new namespace.
+- `uts` sets the uts namespace, either to a path, or if `new` is specified it will use a new namespace.
 - `pid` sets the pid namespace, either to a path, or if `host` is specified it will use the host namespace.
-- `ipc` sets the ipc namespace, either to a path, or if `host` is specified it will use the host namespace.
-- `uts` sets the uts namespace, either to a path, or if `host` is specified it will use the host namespace.
 - `readonly` sets the root filesystem to read only, and changes the other default filesystems to read only.
 - `maskedPaths` sets paths which should be hidden.
 - `readonlyPaths` sets paths to read only.
@@ -88,8 +128,6 @@ For more details see the [OCI specification](https://github.com/opencontainers/r
 - `cgroupsPath` sets the path for cgroups.
 - `sysctl` sets a list of `sysctl` key value pairs that are set inside the container namespace.
 
-Further OCI values will be added, as the list is not yet complete.
-
 ### Mount Options
 When mounting filesystem paths into a container - whether as part of `onboot` or `services` - there are several options of which you need to be aware. Using them properly is necessary for your containers to function properly.