tests: (chrt) improve skip_policy with runtime probe

The skip_policy function relied solely on "chrt --max" output to
detect kernel support for scheduling policies.  This is unreliable
for SCHED_EXT where sched_get_priority_max() returns 0 even on
kernels without CONFIG_SCHED_CLASS_EXT, causing the test to fail
with EINVAL instead of skipping gracefully.

Rework skip_policy to accept optional chrt probe arguments and
verify actual kernel support by attempting to set the policy on
the chrt process itself (--pid 0).  Cache "chrt --max" output once
at startup to avoid repeated execution.

Additionally, filter the platform-dependent runtime parameter from
do_chrt output unless --sched-runtime was explicitly used.  This
removes the need for kernel version gating on the basic batch and
other subtests, allowing them to run on all kernel versions.

Fixes: https://github.com/util-linux/util-linux/issues/4429
Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/tests/ts/chrt/chrt b/tests/ts/chrt/chrt
index 002440109761497d28839bcadb7e0982878e780b..f1aa1243d7308d0cabf5bb20977f5b642c811dbb 100755 (executable)
--- a/tests/ts/chrt/chrt
+++ b/tests/ts/chrt/chrt
@@ -24,17 +24,41 @@ ts_skip_nonroot
 ts_skip_docker
 ts_skip_qemu_user
 
+CHRT_MAX=$($TS_CMD_CHRT --max) || ts_failed "failed to obtain scheduling policies"
+
 function do_chrt {
-       $TS_CMD_CHRT "$@" $TS_CMD_CHRT --pid 0 | sed 's/.* policy: //; s/.* priority: //' >> "$TS_OUTPUT" 2>> "$TS_ERRLOG"
+       local filter='s/.* policy: //; s/.* priority: //'
+       # kernel >= 6.12 reports a platform-dependent default runtime parameter
+       # even without --sched-runtime; filter it out unless explicitly set
+       case "$*" in
+               *--sched-runtime*) ;;
+               *) filter="$filter; /runtime parameter/d" ;;
+       esac
+       $TS_CMD_CHRT "$@" $TS_CMD_CHRT --pid 0 | sed "$filter" >> "$TS_OUTPUT" 2>> "$TS_ERRLOG"
 }
 
+# skip_policy <POLICY_NAME> [chrt-option priority]
 function skip_policy {
-       $TS_CMD_CHRT --max | grep $1 | grep 'priority' &> /dev/null
-       if [ $? == 1 ]; then
+       local name=$1; shift
+
+       if ! echo "$CHRT_MAX" | grep -q "$name.*priority"; then
                ts_skip "unsupported"
                ts_finalize_subtest
                return 1
        fi
+
+       # runtime probe -- verify the kernel actually supports the policy;
+       # last arg is the priority, everything before is the chrt option(s)
+       if [ $# -gt 0 ]; then
+               local probe_args=("$@")
+               local priority="${probe_args[$#-1]}"
+               unset 'probe_args[$#-1]'
+               if ! $TS_CMD_CHRT "${probe_args[@]}" --pid "$priority" 0 >/dev/null 2>&1; then
+                       ts_skip "unsupported by kernel"
+                       ts_finalize_subtest
+                       return 1
+               fi
+       fi
        return 0
 }
 
@@ -44,18 +68,6 @@ function skip_kernel_lt {
                ts_finalize_subtest
                return 1
        fi
-
-       return 0
-}
-
-function skip_kernel_ge {
-       ts_kernel_ver_lt $1 $2 $3
-       if [ $? == 1 ]; then
-               ts_skip "kernel version must be < $1.$2.$3"
-               ts_finalize_subtest
-               return 1
-       fi
-
        return 0
 }
 
@@ -65,7 +77,7 @@ function cleanup_output {
 
 
 ts_init_subtest "fifo"
-if skip_policy SCHED_FIFO; then
+if skip_policy SCHED_FIFO --fifo 1; then
        do_chrt --fifo 1
        do_chrt --fifo 99
        cleanup_output
@@ -74,7 +86,7 @@ fi
 
 
 ts_init_subtest "batch"
-if skip_policy SCHED_BATCH && skip_kernel_ge 6 12 0; then
+if skip_policy SCHED_BATCH --batch 0; then
        do_chrt --batch 0
        cleanup_output
        ts_finalize_subtest
@@ -82,7 +94,7 @@ fi
 
 
 ts_init_subtest "batch-custom-slice"
-if skip_policy SCHED_BATCH && skip_kernel_lt 6 12 0; then
+if skip_policy SCHED_BATCH --batch 0 && skip_kernel_lt 6 12 0; then
        do_chrt --batch --sched-runtime 100000 0
        cleanup_output
        ts_finalize_subtest
@@ -90,7 +102,7 @@ fi
 
 
 ts_init_subtest "other"
-if skip_policy SCHED_OTHER && skip_kernel_ge 6 12 0; then
+if skip_policy SCHED_OTHER --other 0; then
        do_chrt --other 0
        cleanup_output
        ts_finalize_subtest
@@ -98,7 +110,7 @@ fi
 
 
 ts_init_subtest "other-custom-slice"
-if skip_policy SCHED_OTHER && skip_kernel_lt 6 12 0; then
+if skip_policy SCHED_OTHER --other 0 && skip_kernel_lt 6 12 0; then
        do_chrt --other --sched-runtime 100000 0
        cleanup_output
        ts_finalize_subtest
@@ -106,7 +118,7 @@ fi
 
 
 ts_init_subtest "rr"
-if skip_policy SCHED_RR; then
+if skip_policy SCHED_RR --rr 1; then
        do_chrt --rr 1
        do_chrt --rr 99
        cleanup_output
@@ -115,7 +127,7 @@ fi
 
 
 ts_init_subtest "idle"
-if skip_policy SCHED_IDLE; then
+if skip_policy SCHED_IDLE --idle 0; then
        do_chrt --idle 0
        cleanup_output
        ts_finalize_subtest
@@ -123,7 +135,7 @@ fi
 
 
 ts_init_subtest "deadline"
-if skip_policy SCHED_DEADLINE; then
+if skip_policy SCHED_DEADLINE --deadline --sched-period 130000 0; then
        do_chrt --deadline --sched-period 130000 0
        do_chrt --deadline --sched-period 130000 --sched-deadline 120000 0
        do_chrt --deadline --sched-period 130000 --sched-deadline 120000 --sched-runtime 100000 0
@@ -132,7 +144,7 @@ if skip_policy SCHED_DEADLINE; then
 fi
 
 ts_init_subtest "ext"
-if skip_policy SCHED_EXT; then
+if skip_policy SCHED_EXT --ext 0; then
        do_chrt --ext 0
        do_chrt -e 0
        cleanup_output