Re: [PATCH 2/2] sstate: guard sstate funcs against execution in wrong context

["'MOESSBAUER, Felix' via isar-users" <isar-users@googlegroups.com>]

On Thu, 2026-06-25 at 18:43 +0200, Jan Kiszka wrote:
> On 25.06.26 17:02, 'Felix Moessbauer' via isar-users wrote:
> > In sstate.bbclass, sstate_package() sets SSTATE_CURRTASK from
> > the sstate task being packaged, then runs every function listed
> > in SSTATECREATEFUNCS. This happens independent of the context the sstate
> > task is scoped to for all tasks in a single recipe.
> > 
> > While this pattern is not problematic in isar itself (we only have one
> > SSTATECREATEFUNC per recipe), it becomes problematic when downstream
> > users define further manual sstate tasks. In this case, the sstate tasks
> > are executed in the wrong context, leading to races and failures in all
> > colors.
> > 
> > We fix this by guarding each manually defined sstate func to only run in
> > its intended context.
> > 
> > Signed-off-by: Felix Moessbauer <felix.moessbauer@siemens.com>
> > ---
> >  meta/classes-recipe/dpkg-base.bbclass                 | 4 ++++
> >  meta/classes-recipe/rootfs.bbclass                    | 4 ++++
> >  meta/recipes-core/isar-mmdebstrap/isar-mmdebstrap.inc | 4 ++++
> >  3 files changed, 12 insertions(+)
> > 
> > diff --git a/meta/classes-recipe/dpkg-base.bbclass b/meta/classes-recipe/dpkg-base.bbclass
> > index f7a12302..85c37a5a 100644
> > --- a/meta/classes-recipe/dpkg-base.bbclass
> > +++ b/meta/classes-recipe/dpkg-base.bbclass
> > @@ -184,6 +184,8 @@ SSTATECREATEFUNCS += "dpkg_build_sstate_prepare"
> >  SSTATEPOSTINSTFUNCS += "dpkg_build_sstate_finalize"
> >  
> >  dpkg_build_sstate_prepare() {
> > +    [ "${SSTATE_CURRTASK}" = "dpkg_build" ] || return 0
> > +
> >      # this runs in SSTATE_BUILDDIR, which will be deleted automatically
> >      if [ -n "$(find ${WORKDIR} -maxdepth 1 -name '*.deb' -print -quit)" ]; then
> >          cp -f ${WORKDIR}/*.deb -t .
> > @@ -191,6 +193,8 @@ dpkg_build_sstate_prepare() {
> >  }
> >  
> >  dpkg_build_sstate_finalize() {
> > +    [ "${SSTATE_CURRTASK}" = "dpkg_build" ] || return 0
> > +
> >      # this runs in SSTATE_INSTDIR
> >      if [ -n "$(find . -maxdepth 1 -name '*.deb' -print -quit)" ]; then
> >          mv -f ./*.deb -t ${WORKDIR}/
> > diff --git a/meta/classes-recipe/rootfs.bbclass b/meta/classes-recipe/rootfs.bbclass
> > index 8a4aad16..936f56fe 100644
> > --- a/meta/classes-recipe/rootfs.bbclass
> > +++ b/meta/classes-recipe/rootfs.bbclass
> > @@ -691,6 +691,8 @@ SSTATE_TAR_ATTR_FLAGS ?= "--xattrs --xattrs-include='*'"
> >  
> >  # the rootfs is owned by root, so we need some sudoing to pack and unpack
> >  rootfs_install_sstate_prepare() {
> > +    [ "${SSTATE_CURRTASK}" = "rootfs_install" ] || return 0
> > +
> >      # this runs in SSTATE_BUILDDIR, which will be deleted automatically
> >      # tar --one-file-system will cross bind-mounts to the same filesystem,
> >      # so we use some mount magic to prevent that
> > @@ -705,6 +707,8 @@ rootfs_install_sstate_prepare() {
> >  rootfs_install_sstate_prepare[lockfiles] = "${REPO_ISAR_DIR}/isar.lock"
> >  
> >  rootfs_install_sstate_finalize() {
> > +    [ "${SSTATE_CURRTASK}" = "rootfs_install" ] || return 0
> > +
> >      # this runs in SSTATE_INSTDIR
> >      # - after building the rootfs, the tar won't be there, but we also don't need to unpack
> >      # - after restoring from cache, there will be a tar which we unpack and then delete
> > diff --git a/meta/recipes-core/isar-mmdebstrap/isar-mmdebstrap.inc b/meta/recipes-core/isar-mmdebstrap/isar-mmdebstrap.inc
> > index e746f469..98f6c090 100644
> > --- a/meta/recipes-core/isar-mmdebstrap/isar-mmdebstrap.inc
> > +++ b/meta/recipes-core/isar-mmdebstrap/isar-mmdebstrap.inc
> > @@ -264,12 +264,16 @@ SSTATECREATEFUNCS += "bootstrap_sstate_prepare"
> >  SSTATEPOSTINSTFUNCS += "bootstrap_sstate_finalize"
> >  
> >  bootstrap_sstate_prepare() {
> > +    [ "${SSTATE_CURRTASK}" = "bootstrap" ] || return 0
> > +
> >      # this runs in SSTATE_BUILDDIR, which will be deleted automatically
> >      sudo cp -a "${WORKDIR}/rootfs.tar.zst" ./bootstrap.tar.zst
> >      sudo chown $(id -u):$(id -g) bootstrap.tar.zst
> >  }
> >  
> >  bootstrap_sstate_finalize() {
> > +    [ "${SSTATE_CURRTASK}" = "bootstrap" ] || return 0
> > +
> >      # this runs in SSTATE_INSTDIR
> >      # we should restore symlinks after using tar
> >      if [ -f bootstrap.tar.zst ]; then
> 
> Out of curiosity: Does OE have similar setup and solve them the same
> way? Or are we doing something ... special here? 
> 

They use (or nowadays mostly used) this pattern as well. However, this
is only needed when implementing the low-level sstate functions
manually, which should be avoided. When using the task flags (sstate-
inputdirs / sstate-outputdirs) this is not needed. Unfortunately we
need to implement the rootfs part manually, as tarring and untarring
the rootfs can only be performed by root (due to the permissions) and
we also want to avoid having rootfs' tarballs lingering in the workdir.

My hope is that sometime in the future we can solely rely on the task
flags, but this requires more refactoring. The rootless story is part
of it, but does not fully solve this until we drop the old privileged
part (and more ...).

You can also call it technical dept.

> This pattern looks like
> it does not scale very well (easily forgotten when adding another
> function in Isar and even more easily in downstream).

Well... you rarely need to write sstate functions by yourself, but rely
on the inputdirs / outputdirs flags instead. Then it is not needed.

Felix

> 
> Jan
> 
> -- 
> Siemens AG, Foundational Technologies
> Linux Expert Center

-- 
You received this message because you are subscribed to the Google Groups "isar-users" group.
To unsubscribe from this group and stop receiving emails from it, send an email to isar-users+unsubscribe@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/isar-users/fdba43d9e861fc5f4a8ced1e74afd2da3672ad04.camel%40siemens.com.