Re: [RFC v2 19/19] use copy of sbom-chroot for sbom creation

[Uladzimir Bely <ubely@ilbers.de>]

Hello Felix.

On Fri, 2026-02-20 at 18:16 +0100, 'Felix Moessbauer' via isar-users
wrote:
> We previously used the same sbom-chroot for generating the sbom of
> different root filesystems. This required to have a live copy of the
> sbom-chroot in the deploy dir, on which also was operated on.
> Further,
> this copy was left behind in the deploy dir.
> 
> We improve this by just storing a minimized tarball of the sbom-
> chroot
> in the deploy dir and extract that into the workdir of the rootfs.
> 
> Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
> ---
>  meta/classes/sbom.bbclass                     | 29 ++++++++++++++++-
> --
>  .../sbom-chroot/sbom-chroot.bb                | 11 ++++++-
>  2 files changed, 35 insertions(+), 5 deletions(-)
> 
> diff --git a/meta/classes/sbom.bbclass b/meta/classes/sbom.bbclass
> index e3d0e702..69c5d1b0 100644
> --- a/meta/classes/sbom.bbclass
> +++ b/meta/classes/sbom.bbclass
> @@ -23,7 +23,8 @@ SBOM_SPDX_NAMESPACE_PREFIX ?=
> "https://spdx.org/spdxdocs"
>  DEPLOY_DIR_SBOM = "${DEPLOY_DIR_IMAGE}"
>  
>  SBOM_DIR = "${DEPLOY_DIR}/sbom"
> -SBOM_CHROOT = "${SBOM_DIR}/sbom-chroot"
> +SBOM_CHROOT = "${SBOM_DIR}/sbom-chroot.tar.zst"
> +SBOM_CHROOT_LOCAL = "${WORKDIR}/sbom-chroot"

This change also requires appropriate changes in at least image-tools-
extension.bbclass and imagetype_wic.bbclass, e.g.:


diff --git a/meta/classes-recipe/imagetypes_wic.bbclass b/meta/classes-
recipe/imagetypes_wic.bbclass
index ebf3ce8e..34f2286e 100644
--- a/meta/classes-recipe/imagetypes_wic.bbclass
+++ b/meta/classes-recipe/imagetypes_wic.bbclass
@@ -216,13 +216,16 @@ merge_wic_sbom() {
     TIMESTAMP=$(date --iso-8601=s -d @${SOURCE_DATE_EPOCH})
     sbom_document_uuid="${@d.getVar('SBOM_DOCUMENT_UUID') or
generate_document_uuid(d, False)}"
 
+    mkdir -p ${SBOM_CHROOT_LOCAL}
+    tar -xf ${SBOM_CHROOT} -C ${SBOM_CHROOT_LOCAL}
+
     cat ${DEPLOY_DIR_IMAGE}/${IMAGE_FULLNAME}.${bomtype}.json \
         ${DEPLOY_DIR_IMAGE}/${INITRD_DEPLOY_FILE}.${bomtype}.json \
         ${WORKDIR}/imager.${bomtype}.json 2>/dev/null | \
     bwrap \
         --unshare-user \
         --unshare-pid \
-        --bind ${SBOM_CHROOT} / \
+        --bind ${SBOM_CHROOT_LOCAL} / \
         -- debsbom -v merge -t $BOMTYPE \
             --distro-name '${SBOM_DISTRO_NAME}-Image' --distro-
supplier '${SBOM_DISTRO_SUPPLIER}' \
             --distro-version '${SBOM_DISTRO_VERSION}' --base-distro-
vendor '${SBOM_BASE_DISTRO_VENDOR}' \


Without it, in my build this failed at wic stage (qemuamd64 target)
when attempting to bind-mount tar.zst:


bwrap --unshare-user --unshare-pid --bind
 /work/build/tmp/deploy/sbom/sbom-chroot.tar.zst / -- debsbom -v merge
-t spdx --distro-name ISAR-Debian-GNU-Linux-Image --distro-supplier
ISAR --distro-version 1 --base-distro-vendor debian --cdx-serialnumber
4641ea56-9fce-4120-ae90-0784cd98d434 --spdx-namespace
https://spdx.org/spdxdocs-4641ea56-9fce-4120-ae90-0784cd98d434 --
timestamp 2024-03-04T18:14:11+03:00 - -o -

bwrap: Can't create file at /: Is a directory


>  
>  # adapted from the isar-cip-core image_uuid.bbclass
>  def generate_document_uuid(d, warn_not_repr=True):
> @@ -40,14 +41,25 @@ def sbom_doc_uuid(d):
>      if not d.getVar("SBOM_DOCUMENT_UUID"):
>          d.setVar("SBOM_DOCUMENT_UUID", generate_document_uuid(d))
>  
> +prepare_sbom_chroot() {
> +    create_chroot_parent_dir ${WORKDIR}
> +    run_privileged_heredoc <<'EOF'
> +        set -e
> +        mkdir -p ${SBOM_CHROOT_LOCAL}
> +        tar -xf ${SBOM_CHROOT} -C ${SBOM_CHROOT_LOCAL}
> +EOF
> +}
> +
>  generate_sbom() {
> -    run_privileged mkdir -p ${SBOM_CHROOT}/mnt/rootfs
> ${SBOM_CHROOT}/mnt/deploy-dir
> +    run_privileged mkdir -p \
> +        ${SBOM_CHROOT_LOCAL}/mnt/rootfs \
> +        ${SBOM_CHROOT_LOCAL}/mnt/deploy-dir
>  
>      TIMESTAMP=$(date --iso-8601=s -d @${SOURCE_DATE_EPOCH})
>      bwrap \
>          --unshare-user \
>          --unshare-pid \
> -        --bind ${SBOM_CHROOT} / \
> +        --bind ${SBOM_CHROOT_LOCAL} / \
>          --bind ${ROOTFSDIR} /mnt/rootfs \
>          --bind ${DEPLOY_DIR_SBOM} /mnt/deploy-dir \
>          -- debsbom -v generate ${SBOM_DEBSBOM_TYPE_ARGS} -r
> /mnt/rootfs -o /mnt/deploy-dir/'${PN}-${DISTRO}-${MACHINE}' \
> @@ -59,8 +71,17 @@ generate_sbom() {
>              --timestamp $TIMESTAMP ${SBOM_DEBSBOM_EXTRA_ARGS}
>  }
>  
> +cleanup_sbom_chroot() {
> +    run_privileged rm -rf ${SBOM_CHROOT_LOCAL}
> +}
> +
>  do_generate_sbom[dirs] += "${DEPLOY_DIR_SBOM}"
> +do_generate_sbom[network] = "${TASK_USE_SUDO}"
>  python do_generate_sbom() {
>      sbom_doc_uuid(d)
> -    bb.build.exec_func("generate_sbom", d)
> +    try:
> +        bb.build.exec_func("prepare_sbom_chroot", d)
> +        bb.build.exec_func("generate_sbom", d)
> +    finally:
> +        bb.build.exec_func("cleanup_sbom_chroot", d)
>  }
> diff --git a/meta/recipes-devtools/sbom-chroot/sbom-chroot.bb
> b/meta/recipes-devtools/sbom-chroot/sbom-chroot.bb
> index bf6d6683..fec1f502 100644
> --- a/meta/recipes-devtools/sbom-chroot/sbom-chroot.bb
> +++ b/meta/recipes-devtools/sbom-chroot/sbom-chroot.bb
> @@ -27,7 +27,16 @@ ROOTFSDIR = "${WORKDIR}/rootfs"
>  ROOTFS_PACKAGES = "${SBOM_IMAGE_INSTALL}"
>  
>  do_sbomchroot_deploy[dirs] = "${SBOM_DIR}"
> +do_sbomchroot_deploy[network] = "${TASK_USE_SUDO}"
>  do_sbomchroot_deploy() {
> -    ln -Tfsr "${ROOTFSDIR}" "${SBOM_CHROOT}"
> +    # deploy with empty var to make it smaller
> +    lopts="--one-file-system --exclude=var/*"
> +    ZSTD="zstd -${SSTATE_ZSTD_CLEVEL} -T${ZSTD_THREADS}"
> +
> +    run_privileged \
> +        tar -C ${ROOTFSDIR} -cpS $lopts ${ROOTFS_TAR_ATTR_FLAGS} . \
> +            | $ZSTD > ${SBOM_CHROOT}
> +    # cleanup extracted rootfs
> +    run_privileged rm -rf ${ROOTFSDIR}
>  }
>  addtask do_sbomchroot_deploy before do_build after do_rootfs
> -- 
> 2.51.0

-- 
Best regards,
Uladzimir.

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