fs: new OCI filesystem type

Add support to generate OCI (Open Container Initiative) images.

An OCI image consists of a manifest, an image index (optional), a set of
filesystem layers, and a configuration. The complete specification is
available in the link below:

https://github.com/opencontainers/image-spec/blob/master/spec.md

The image is generated with the host tool sloci-image, and config
options can be used to configure image parameters.

By default, the image is generated in a directory called rootfs-oci:

$ cd output/images
$ ls rootfs-oci/
blobs  index.json  oci-layout

Optionally, the image can be packed into a tar archive.

The image can be pushed to a registry using containers tools like
skopeo:

$ skopeo copy --dest-creds <user>:<pass> oci:rootfs-oci:<tag> \
	docker://<user>/<image>[:tag]

And then we can pull/run the container image with tools like docker:

$ docker run -it <user>/<image>[:tag]

Signed-off-by: Sergio Prado <sergio.prado@e-labworks.com>
Signed-off-by: Matthew Weber <matthew.weber@collins.com>
[Arnout:
 - mention in help text that options are space separated;
 - use GO_GOARCH and GO_GOARM for architecture;
 - quote all arguments;
 - don't cd to BINARIES_DIR;
 - remove ROOTFS_OCI_IMAGE_NAME variable;
 - remove wildcard from rm.
]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

fs/Config.in

@@ -11,6 +11,7 @@ source "fs/f2fs/Config.in"
 source "fs/initramfs/Config.in"
 source "fs/iso9660/Config.in"
 source "fs/jffs2/Config.in"
+source "fs/oci/Config.in"
 source "fs/romfs/Config.in"
 source "fs/squashfs/Config.in"
 source "fs/tar/Config.in"

fs/oci/Config.in

@@ -0,0 +1,89 @@
+config BR2_TARGET_ROOTFS_OCI
+	bool "oci image"
+	help
+	  Build an OCI (Open Container Initiative) image.
+
+	  By default, the image is generated in a directory called
+	  rootfs-oci:
+
+	  $ cd output/images
+	  $ ls rootfs-oci/
+	  blobs  index.json  oci-layout
+
+	  You can push the image to a registry. Example using skopeo:
+
+	  $ skopeo copy --dest-creds <user>:<pass> \
+	           oci:rootfs-oci:<tag> docker://<user>/<image>[:tag]
+
+	  And pull/run it with docker:
+
+	  $ docker run -it <user>/<image>[:tag]
+
+if BR2_TARGET_ROOTFS_OCI
+
+config BR2_TARGET_ROOTFS_OCI_AUTHOR
+	string "author name and/or email address"
+	default "Buildroot"
+	help
+	  Name and/or email address of the person which created the
+	  image.
+
+config BR2_TARGET_ROOTFS_OCI_TAG
+	string "image tag"
+	default "latest"
+	help
+	  Tag to be used in the container image. If empty, 'latest' will
+	  be used by default.
+
+config BR2_TARGET_ROOTFS_OCI_ENTRYPOINT
+	string "entrypoint"
+	default "sh"
+	help
+	  Command to execute when the container starts.
+
+config BR2_TARGET_ROOTFS_OCI_ENTRYPOINT_ARGS
+	string "entrypoint arguments"
+	help
+	  Default arguments to the entrypoint of the container.
+
+config BR2_TARGET_ROOTFS_OCI_WORKDIR
+	string "working directory"
+	help
+	  Working directory of the entrypoint process in the
+	  container.
+
+config BR2_TARGET_ROOTFS_OCI_UID
+	string "username or UID"
+	default "0"
+	help
+	  The username or UID of user the process run as.
+
+config BR2_TARGET_ROOTFS_OCI_ENV_VARS
+	string "environment variables"
+	help
+	  Default environment variables for the container.
+	  Space-separated list of variable=value assignments.
+
+config BR2_TARGET_ROOTFS_OCI_PORTS
+	string "ports"
+	help
+	  Default set of ports to expose from a container running
+	  this image as a space-separted list of ports in the following
+	  format:
+
+	  <port>/tcp, <port>/udp, <port> (same as <port>/tcp).
+
+config BR2_TARGET_ROOTFS_OCI_LABELS
+	string "labels"
+	help
+	  Metadata in the format KEY=VALUE for the container compliant
+	  with OCI annotation rules. If KEY starts with a dot, it will
+	  be prefixed with "org.opencontainers.image"
+	  (e.g. .url -> org.opencontainers.image.url).
+
+config BR2_TARGET_ROOTFS_OCI_ARCHIVE
+	bool "pack oci image into a tar archive"
+	help
+	  Select whether the image should be packed into a TAR archive.
+
+endif

fs/oci/oci.mk

@@ -0,0 +1,80 @@
+################################################################################
+#
+# Build the oci image
+#
+################################################################################
+
+ROOTFS_OCI_DEPENDENCIES = host-sloci-image
+
+# architecture - take it from Go
+OCI_SLOCI_IMAGE_OPTS = --arch $(GO_GOARCH)
+
+# architecture variant (typically used only for arm)
+OCI_SLOCI_IMAGE_OPTS += $(and $(GO_GOARM),--arch-variant v$(GO_GOARM))
+
+# entrypoint
+OCI_ENTRYPOINT = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_ENTRYPOINT))
+ifneq ($(OCI_ENTRYPOINT),)
+OCI_SLOCI_IMAGE_OPTS += --entrypoint "$(OCI_ENTRYPOINT)"
+endif
+
+# entrypoint arguments
+OCI_ENTRYPOINT_ARGS = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_ENTRYPOINT_ARGS))
+ifneq ($(OCI_ENTRYPOINT_ARGS),)
+OCI_SLOCI_IMAGE_OPTS += --cmd "$(OCI_ENTRYPOINT_ARGS)"
+endif
+
+# author
+OCI_AUTHOR = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_AUTHOR))
+ifneq ($(OCI_AUTHOR),)
+OCI_SLOCI_IMAGE_OPTS += --author "$(OCI_AUTHOR)"
+endif
+
+# username or UID
+OCI_UID = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_UID))
+ifneq ($(OCI_UID),)
+OCI_SLOCI_IMAGE_OPTS += --user "$(OCI_UID)"
+endif
+
+# labels
+OCI_LABELS = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_LABELS))
+ifneq ($(OCI_LABELS),)
+OCI_SLOCI_IMAGE_OPTS += \
+	$(foreach label,$(OCI_LABELS),--label "$(label)")
+endif
+
+# environment variables
+OCI_ENV_VARS = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_ENV_VARS))
+ifneq ($(OCI_ENV_VARS),)
+OCI_SLOCI_IMAGE_OPTS += \
+	$(foreach var,$(OCI_ENV_VARS),--env "$(var)")
+endif
+
+# working directory
+OCI_WORKDIR = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_WORKDIR))
+ifneq ($(OCI_WORKDIR),)
+OCI_SLOCI_IMAGE_OPTS += --working-dir "$(OCI_WORKDIR)"
+endif
+
+# ports
+OCI_PORTS = $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_PORTS))
+ifneq ($(OCI_PORTS),)
+OCI_SLOCI_IMAGE_OPTS += \
+	$(foreach port,$(OCI_PORTS),--port "$(port)")
+endif
+
+# tag
+OCI_TAG = $(or $(call qstrip,$(BR2_TARGET_ROOTFS_OCI_TAG)),latest)
+
+# enable tar archive
+ifeq ($(BR2_TARGET_ROOTFS_OCI_ARCHIVE),y)
+OCI_SLOCI_IMAGE_OPTS += --tar
+endif
+
+define ROOTFS_OCI_CMD
+	rm -rf $(BINARIES_DIR)/rootfs-oci
+	$(HOST_DIR)/bin/sloci-image $(OCI_SLOCI_IMAGE_OPTS) $(TARGET_DIR) \
+		$(BINARIES_DIR)/rootfs-oci:$(OCI_TAG)
+endef
+
+$(eval $(rootfs))