virtio: add script and make target to build ext2 device

3 files changed, 19 insertions, 10 deletions

diff --git a/content/2021-12-02-toying-with-virtio.md b/content/2021-12-02-toying-with-virtio.md
index a46fb2a..56c34de 100644
--- a/content/2021-12-02-toying-with-virtio.md
+++ b/content/2021-12-02-toying-with-virtio.md
@@ -132,11 +132,7 @@ Next we are creating the ext2 filesystem image. This we'll do by creating an
 `128M` blob and format it with ext2 afterwards. Then we can mount the image
 via a `loop` device and populate the filesystem.
 ```sh
-dd if=/dev/zero of=rootfs.ext2 bs=1M count=128
-mkfs.ext2 rootfs.ext2
-mount -t ext2 -o loop rootfs.ext2 /mnt
-echo world > /mnt/hello
-umount /mnt
+{{ include_range(path="content/2021-12-02-toying-with-virtio/build_ext2.sh", start=3, end=7) }}
 ```
 
 Before booting the guest we will attach the virtio block device to the VM.
@@ -145,7 +141,7 @@ Therefore we add the `-drive` configuration to our previous qemu invocation.
 ```sh
 qemu-system-x86_64 \
   ...
-  -drive if=virtio,file=rootfs.ext2,format=raw
+  -drive if=virtio,file=fs.ext2,format=raw
 ```
 
 The `-drive` option is a shortcut for a `-device (front-end) / -blockdev
@@ -339,6 +335,7 @@ following files:
 - [Makefile][makefile]
 - [build_initramfs.sh][build-initramfs]
 - [build_kernel.sh][build-kernel]
+- [build_ext2.sh][build-ext2]
 
 Then run the following steps to build everything. The prefix `[H]` and `[C]`
 indicate whether this command is run on the host or inside the container
@@ -355,9 +352,8 @@ respectively.
 # Build kernel and initramfs.
 [C]: make
 
-# Create the rootfs.ext2 disk image as described in the virtio blk
-# section above, or remove the drive from the qemu command line
-# in the make `run` target.
+# Build ext2 fs as virtio blkdev backend.
+[H]: make ext2
 
 # Start qemu guest.
 [H]: make run
@@ -365,6 +361,7 @@ respectively.
 
 [build-initramfs]: https://git.memzero.de/johannst/blog/src/branch/main/content/2021-12-02-toying-with-virtio/build_initramfs.sh
 [build-kernel]: https://git.memzero.de/johannst/blog/src/branch/main/content/2021-12-02-toying-with-virtio/build_kernel.sh
+[build-ext2]: https://git.memzero.de/johannst/blog/src/branch/main/content/2021-12-02-toying-with-virtio/build_ext2.sh
 [makefile]: https://git.memzero.de/johannst/blog/src/branch/main/content/2021-12-02-toying-with-virtio/Makefile
 [dockerfile]: https://git.memzero.de/johannst/blog/src/branch/main/content/2021-12-02-toying-with-virtio/Dockerfile
 [initramfs]: https://www.kernel.org/doc/Documentation/filesystems/ramfs-rootfs-initramfs.txt
diff --git a/content/2021-12-02-toying-with-virtio/Makefile b/content/2021-12-02-toying-with-virtio/Makefile
index 4009862..d4286af 100644
--- a/content/2021-12-02-toying-with-virtio/Makefile
+++ b/content/2021-12-02-toying-with-virtio/Makefile
@@ -6,6 +6,7 @@ help:
 	@echo "Build targets:"
 	@echo "* init       - Build busybox based initramfs."
 	@echo "* kernel     - Build minimal linux kernel."
+	@echo "  ext2       - Build minimal ext2 fs as virtio blkdev backend (uses sudo)."
 	@echo "  clean      - Cleanup downloads & builds."
 	@echo ""
 	@echo "Run targets:"
@@ -27,6 +28,9 @@ kernel:
 init:
 	./build_initramfs.sh
 
+ext2:
+	./build_ext2.sh
+
 run:
 	qemu-system-x86_64                                            \
 	  -nographic                                                  \
@@ -38,7 +42,7 @@ run:
 	  -device virtio-serial-pci                                   \
 	  -device virtconsole,chardev=vcon,name=console.0             \
 	  -chardev socket,id=vcon,ipv4=on,host=localhost,port=2222,server,telnet=on,wait=off \
-	  -drive format=raw,if=virtio,file=rootfs.ext2 \
+	  -drive format=raw,if=virtio,file=blk.ext2 \
 	  -nic user,model=virtio-net-pci
 
 vcon:
@@ -48,6 +52,7 @@ clean:
 	$(RM) initramfs.cpio.gz
 	$(RM) -r busybox-*
 	$(RM) -r linux-$(VER)*
+	$(RM) blk.ext2
 
 docker:
 	DOCKER_BUILDKIT=1 docker build --build-arg UID=$(shell id -u) -t virtio-dev .
diff --git a/content/2021-12-02-toying-with-virtio/build_ext2.sh b/content/2021-12-02-toying-with-virtio/build_ext2.sh
new file mode 100755
index 0000000..6e6bff8
--- /dev/null
+++ b/content/2021-12-02-toying-with-virtio/build_ext2.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+dd if=/dev/zero of=blk.ext2 bs=1M count=128
+mkfs.ext2 blk.ext2
+sudo mount -t ext2 -o loop blk.ext2 /mnt
+echo world | sudo tee /mnt/hello
+sudo umount /mnt