test: try to make TEST-04-JOURNAL.journalctl-varlink less flaky

The io.systemd.JournalAccess server occasionally returns NoEntries for a
unit-filter query right after the unit logged its message, e.g. from a
failing CI run:

 [ 1204.967910] TEST-04-JOURNAL.sh[15025]: ++ varlinkctl call --more /run/systemd/io.systemd.JournalAccess io.systemd.JournalAccess.GetEntries '{"units": ["test-journalctl-varlink-1-13583.service", "test-journalctl-varlink-2-25039.service"]}'
 [ 1205.017361] journalctl[15026]: varlink-3-3: Received message: {"method":"io.systemd.JournalAccess.GetEntries","parameters":{"units":["test-journalctl-varlink-1-13583.service","test-journalctl-varlink-2-25039.service"]},"more":true}
 [ 1205.017498] journalctl[15026]: Failed to open journal file /var/log/journal/ce54feb228124e639f3b7779beeaff60/system.journal: No data available
 [ 1205.017823] journalctl[15026]: varlink-3-3: Sending message: {"error":"io.systemd.JournalAccess.NoEntries"}
 [ 1205.017936] TEST-04-JOURNAL.sh[15025]: Method call failed: io.systemd.JournalAccess.NoEntries
 [ 1205.499083] TEST-04-JOURNAL.sh[146]: Subtest /usr/lib/systemd/tests/testdata/units/TEST-04-JOURNAL.journalctl-varlink.sh failed

Wrap the calls that expect data in a helper that retries up to 3 times on
NoEntries, syncing the journal between attempts.

Follow-up for a109189fab

Co-developed-by: Claude Opus 4.7 <noreply@anthropic.com>

test/units/TEST-04-JOURNAL.journalctl-varlink.sh

@@ -5,6 +5,26 @@ set -o pipefail
 
 VARLINK_SOCKET="/run/systemd/io.systemd.JournalAccess"
 
+# Wrapper around varlinkctl that retries up to 3 times when the server returns
+# NoEntries to avoid spurious flaky failures
+varlinkctl_get_entries() {
+    local output rc
+    for _ in 1 2 3; do
+        output="$(varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries "$@" 2>&1)" && rc=0 || rc=$?
+        if [[ $rc -eq 0 ]]; then
+            printf '%s\n' "$output"
+            return 0
+        fi
+        if ! grep -q 'io.systemd.JournalAccess.NoEntries' <<<"$output"; then
+            printf '%s\n' "$output" >&2
+            return $rc
+        fi
+        journalctl --sync || true
+    done
+    printf '%s\n' "$output" >&2
+    return $rc
+}
+
 # ensure the varlink basics work
 varlinkctl list-interfaces "$VARLINK_SOCKET" | grep io.systemd.JournalAccess
 varlinkctl introspect "$VARLINK_SOCKET" | grep "method GetEntries("
@@ -16,18 +36,18 @@ systemd-cat -t "$TAG" -p warning echo "varlink-test-warning"
 journalctl --sync
 
 # most basic call works
-varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries '{}' | jq --seq .
+varlinkctl_get_entries '{}' | jq --seq .
 # validate the JSON has some basic properties (similar to journalctls json output)
-varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries '{}' | jq --seq '.entry | {MESSAGE, PRIORITY, _UID}'
+varlinkctl_get_entries '{}' | jq --seq '.entry | {MESSAGE, PRIORITY, _UID}'
 
 # check that default limit works (100), we don't know how many entries we have so we just check
 # bounds
-ENTRIES=$(varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries '{}' | wc -l)
+ENTRIES=$(varlinkctl_get_entries '{}' | wc -l)
 test "$ENTRIES" -gt 0
 test "$ENTRIES" -le 100
 
 # check explicit limit
-ENTRIES=$(varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries '{"limit": 3}' | wc -l)
+ENTRIES=$(varlinkctl_get_entries '{"limit": 3}' | wc -l)
 test "$ENTRIES" -le 3
 
 # check unit filter: use transient units to get deterministic results
@@ -38,16 +58,16 @@ systemd-run --unit="$UNIT_NAME_2" --wait bash -c 'echo hello-from-varlink-test-2
 journalctl --sync
 
 # single unit filter
-SINGLE_OUTPUT="$(varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries "{\"units\": [\"$UNIT_NAME_1\"]}")"
+SINGLE_OUTPUT="$(varlinkctl_get_entries "{\"units\": [\"$UNIT_NAME_1\"]}")"
 grep "hello-from-varlink-test-1" >/dev/null <<<"$SINGLE_OUTPUT"
 (! grep "hello-from-varlink-test-2" >/dev/null <<<"$SINGLE_OUTPUT")
 # multi unit filter
-MULTI_OUTPUT="$(varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries "{\"units\": [\"$UNIT_NAME_1\", \"$UNIT_NAME_2\"]}")"
+MULTI_OUTPUT="$(varlinkctl_get_entries "{\"units\": [\"$UNIT_NAME_1\", \"$UNIT_NAME_2\"]}")"
 grep "hello-from-varlink-test-1" >/dev/null <<<"$MULTI_OUTPUT"
 grep "hello-from-varlink-test-2" >/dev/null <<<"$MULTI_OUTPUT"
 
 # check priority filter: priority 4 (warning) should include our warning message
-varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries '{"priority": 4, "limit": 1000}' | grep "varlink-test-warning" >/dev/null
+varlinkctl_get_entries '{"priority": 4, "limit": 1000}' | grep "varlink-test-warning" >/dev/null
 # check priority filter: priority 3 (error) should NOT include our warning (priority 4)
 (! varlinkctl call --more "$VARLINK_SOCKET" io.systemd.JournalAccess.GetEntries '{"priority": 3, "limit": 1000}' | grep "varlink-test-warning")