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5b1ac36626
Add a self-contained "devkit" guest extension: a minimal Ubuntu (glibc + busybox + apt) rootfs with common debug tools prebaked (strace, ltrace, iproute2, procps, lsof, tcpdump, pciutils, util-linux, ...), built as a measured erofs+dm-verity image mounted at /run/kata-extensions/devkit. The production guest rootfs is minimal (and, for some bases, shell-less), so the agent debug console has no rich interactive shell. Rather than rebuilding the whole rootfs with debug tooling, this optional extension can be cold-plugged alongside any base image. At runtime the guest helper scripts overlay a writable tmpfs on the read-only extension and chroot in, so apt and every tool run natively against a normal root filesystem; `apt install <pkg>` inside the debug shell pulls anything else into the overlay on demand. busybox-static (/usr/bin/busybox.static) bootstraps the overlay/chroot from the shell-less base (the guest's dynamic loader is not present there yet); it is installed at a dedicated path so it never clobbers the extension's own busybox or /bin/sh, which are needed unclobbered inside the chroot. The rootfs is built through osbuilder (rootfs.sh, with a ROOTFS_ONLY mode that skips the agent/systemd setup) using mmdebstrap, the same tool the base guest rootfs uses, so the devkit needs no bespoke chroot or docker-export logic. The resulting tree is handed to image_builder.sh (mirroring the CoCo extension): it ships no kata-agent, kernel or driver userspace. No runtime wiring is added here; that follows in later commits. Nothing consumes the image yet. Signed-off-by: Fabiano Fidêncio <ffidencio@nvidia.com> Assisted-by: Cursor <cursoragent@cursor.com>