tests: nproc: add a test for cgroup quotas

* tests/nproc/nproc-quota.sh: New root only test.
* tests/local.mk: Reference the new test.

tests/local.mk

@@ -126,6 +126,7 @@ all_root_tests =				\
   tests/ls/capability.sh			\
   tests/ls/no-cap.sh				\
   tests/ls/nameless-uid.sh			\
+  tests/nproc/nproc-quota.sh			\
   tests/chcon/chcon.sh				\
   tests/chroot/chroot-credentials.sh		\
   tests/misc/selinux.sh				\

tests/nproc/nproc-quota.sh

@@ -0,0 +1,85 @@
+#!/bin/sh
+# Ensure that "nproc" honors cgroup quotas
+
+# Copyright (C) 2025 Free Software Foundation, Inc.
+
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+. "${srcdir=.}/tests/init.sh"; path_prepend_ ./src
+print_ver_ nproc
+require_root_
+
+# We could look for modifiable cgroup quotas on the current system,
+# but that would be dangerous to modify and restore robustly.
+# Instead simulate the queried cgroup files in a chroot.
+# For recipes for testing with real cgroups see
+# the comment in: gnulib/tests/test-nproc.c
+
+ROOT=cgroup
+{
+  mkdir -p $ROOT/proc/self &&
+  mkdir -p $ROOT/sys/fs/cgroup/foo &&
+  touch $ROOT/sys/fs/cgroup/cgroup.controllers &&
+  echo '0::/foo' > $ROOT/proc/self/cgroup &&
+  echo 'max 100000' > $ROOT/sys/fs/cgroup/foo/cpu.max  # ignored
+} || framework_failure_
+
+nproc=$abs_top_builddir/src/nproc$EXEEXT
+cp --parents $(ldd $nproc | grep -o '/[^ ]*') $ROOT ||
+  skip_ 'Failed to copy nproc libs to chroot'
+cp $nproc $ROOT || framework_failure_
+chroot $ROOT /nproc --version ||
+  skip_ 'Failed to execute nproc in chroot'
+
+unset OMP_NUM_THEADS
+unset OMP_THREAD_LIMIT
+
+ncpus=$(nproc) || fail=1
+
+# Avoid the following block if the system may
+# already have CPU quotas set, as our simulation
+# would then not match $ncpus
+if test "$ncpus" = "$(nproc --all)"; then
+echo 'max 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq $ncpus || fail=1
+# Note Linux won't allow values > 1,000,000 (i.e., micro seconds)
+# so no point testing above that threshold ( for e.g $((1<<53)) )
+echo "1000000 1" > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq $ncpus || fail=1
+# Can't happen in real cgroup, but ensure we avoid divide by zero
+echo '100000 0' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq $ncpus || fail=1
+echo '100000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(OMP_NUM_THREADS=$ncpus chroot $ROOT /nproc) -eq $ncpus || fail=1
+fi
+
+echo '40000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq 1 || fail=1
+echo '50000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq 1 || fail=1
+echo '100000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq 1 || fail=1
+echo '140000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq 1 || fail=1
+echo '1 1000000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq 1 || fail=1
+
+if test $ncpus -gt 1; then
+echo '150000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(chroot $ROOT /nproc) -eq 2 || fail=1
+echo '150000 100000' > $ROOT/sys/fs/cgroup/cpu.max &&
+test $(OMP_THREAD_LIMIT=10 chroot $ROOT /nproc) -eq 2 || fail=1
+fi
+
+Exit $fail