Add minimal-system-image-x86_64

This element produces a disk image that boots in QEMU. It has a kernel,
BusyBox, and little else; but should be suitable as a basis for more
grand endeavours.

This disk image we produce is 53MB. I spent a while trying to get this
as small as possible and this is as far as I got:

  * The boot partition seems to have a minimum size just over 32MB;
    lower than that and SYSLINUX fails to write the boot sector. The
    combined size of the initramfs and kernel is about 32MB, so I
    imagine that's what limits us.

  * The main partition is limited in size only by the amount of binaries
    that we put there.

  * We have a useless 40KB swap partition, which the x86image plugin
    insists on creating for us. Again 40KB is the minimum size that
    `mkswap` will allow. It's possible to override or modify the
    x86image plugin to avoid swap altogether but I'm not sure of the
    best way to proceed.

There are a few dependency cleanups in the bsp-generic stack; previously
we'd build the whole 'foundation' stack which took ages and wasn't
needed at all.

1 files changed, 37 insertions, 0 deletions

diff --git a/elements/systems/minimal-system-image-x86_64.bst b/elements/systems/minimal-system-image-x86_64.bst
new file mode 100644
index 00000000..d92d5fd5
--- /dev/null
+++ b/elements/systems/minimal-system-image-x86_64.bst
@@ -0,0 +1,37 @@
+kind: buildstream-external:x86image
+description: Create a deployment of the minimal system
+depends:
+- filename: systems/minimal-system.bst
+  type: build
+- filename: deploy-tools.bst
+  type: build
+
+variables:
+  # Size of the disk to create
+  #
+  # Should be able to calculate this based on the space
+  # used, however it must be a multiple of (63 * 512) bytes
+  # as mtools wants a size that is devisable by sectors (512 bytes)
+  # per track (63).
+  #
+  # This is the smallest boot partition I managed to make.
+  boot-size: 33516K
+
+  rootfs-size: 20M
+  sector-size: 512
+  swap-size: 40K
+
+  kernel-args: root=/dev/sda2 rootfstype=ext4 init=/sbin/init console=ttyS0
+
+config:
+  base: deploy-tools.bst
+  input: systems/minimal-system.bst
+
+  final-commands:
+    (>):
+    - |
+      cat > %{install-root}/run-in-qemu.sh << EOF
+      #!/bin/sh
+      qemu-system-x86_64 -drive file=sda.img,format=raw -nographic
+      EOF
+      chmod +x %{install-root}/run-in-qemu.sh