cosim-gpu: Skill for Claude Code

Cosim Disk Image Edit

Modify a standalone copy of the vHost disk and launch it with an explicit kernel and disk configuration.

Prerequisites

• Use a Linux host with guestmount, guestunmount, qemu-img and GNU coreutils.
• Stop processes using the disk before mounting it. Keep the source recipe bundle idle while copying its kernel and disk.
• Allow space for a standalone copy of the QCOW2 image (56 GB virtual capacity).

pgrep -af 'qemu-system-x86_64|cosim_launch.sh|run_cosim_tests.sh' && echo "STOP COSIM FIRST" || echo "OK"
command -v guestmount guestunmount qemu-img timeout tail

Prepare the editable image

Recipe bundles under build/images/ are verified build artifacts. Preserve their disk, kernel, manifest and verification records. A vhost.image selection verifies its bundle and rebuilds a modified artifact before launch.

Verify the source bundle, then create a standalone disk and matching kernel in a new directory under build/image-edits/. This directory is ignored by Git. Use a fresh directory for each edited image; the commands below reject an existing destination.

set -euo pipefail
SOURCE_BUNDLE="$PWD/build/images/ubuntu/24.04/x86_64/rocm/7.0"
CUSTOM_DIR="$PWD/build/image-edits/rocm70"
just ci-rocm-assets verify ubuntu/24.04/x86_64/rocm/7.0
test ! -e "$CUSTOM_DIR"
mkdir -p "$CUSTOM_DIR"
cp "$SOURCE_BUNDLE/kernel" "$CUSTOM_DIR/kernel"
qemu-img convert -f qcow2 -O qcow2 "$SOURCE_BUNDLE/disk" "$CUSTOM_DIR/disk.qcow2"

Keep the copied kernel paired with the disk's installed kernel modules. Changes to the kernel require exporting the corresponding boot artifacts as well.

Mount

DISK="$CUSTOM_DIR/disk.qcow2"
MOUNTPOINT="$CUSTOM_DIR/mount"
mkdir -p "$MOUNTPOINT"
guestmount -a "$DISK" -i --rw --pid-file "$CUSTOM_DIR/guestmount.pid" "$MOUNTPOINT"

Edit scope

Supported edit classes:

• Add or replace files under the vHost filesystem.
• Add or update systemd units and matching enablement symlinks.
• Add or update kernel module configuration under /etc/modprobe.d/.
• Install ROCm runtime debug components through repository scripts when the task is runtime debugging.
• Inspect disk layout with qemu-img info "$DISK" if guestmount cannot inspect the image.