CI: system tests: make random_free_port() parallel-safe

...by using a crude port lock-and-reserve mechanism. This is
a small cherrypick from code that has been working in #23275
over dozens of CI runs. Am separating out into a small PR
because it's stable, harmless to serial runs, and will
simplify the eventual review of #23275.

Closes: #23488

Signed-off-by: Ed Santiago <santiago@redhat.com>

test/system/helpers.bash

@@ -41,6 +41,9 @@ if [ $(id -u) -eq 0 ]; then
     _LOG_PROMPT='#'
 fi
 
+# Used in helpers.network, needed here in teardown
+PORT_LOCK_DIR=$BATS_SUITE_TMPDIR/reserved-ports
+
 ###############################################################################
 # BEGIN tools for fetching & caching test images
 #
@@ -205,6 +208,14 @@ function defer-assertion-failures() {
 function basic_teardown() {
     echo "# [teardown]" >&2
 
+    # Free any ports reserved by our test
+    if [[ -d $PORT_LOCK_DIR ]]; then
+        mylocks=$(grep -wlr $BATS_SUITE_TEST_NUMBER $PORT_LOCK_DIR || true)
+        if [[ -n "$mylocks" ]]; then
+            rm -f $mylocks
+        fi
+    fi
+
     immediate-assertion-failures
     # Unlike normal tests teardown will not exit on first command failure
     # but rather only uses the return code of the teardown function.

test/system/helpers.network.bash

@@ -273,6 +273,36 @@ function ether_get_name() {
 
 ### Ports and Ranges ###########################################################
 
+# reserve_port() - create a lock file reserving a port, or return false
+function reserve_port() {
+    local port=$1
+
+    mkdir -p $PORT_LOCK_DIR
+    local lockfile=$PORT_LOCK_DIR/$port
+    local locktmp=$PORT_LOCK_DIR/.$port.$$
+    echo $BATS_SUITE_TEST_NUMBER >$locktmp
+
+    if ln $locktmp $lockfile; then
+        rm -f $locktmp
+        return
+    fi
+    # Port already reserved
+    rm -f $locktmp
+    false
+}
+
+# unreserve_port() - free a temporarily-reserved port
+function unreserve_port() {
+    local port=$1
+
+    local lockfile=$PORT_LOCK_DIR/$port
+    -e $lockfile || die "Cannot unreserve non-reserved port $port"
+    assert "$(< $lockfile)" = "$BATS_SUITE_TEST_NUMBER" \
+           "Port $port is not reserved by this test"
+    rm -f $lockfile
+}
+
+
 # random_free_port() - Get unbound port with pseudorandom number
 # $1:	Optional, dash-separated interval, [5000, 5999] by default
 # $2:	Optional binding address, any IPv4 address by default
@@ -284,9 +314,14 @@ function random_free_port() {
 
     local port
     for port in $(shuf -i ${range}); do
-        if port_is_free $port $address $protocol; then
-            echo $port
-            return
+        # First make sure no other tests are using it
+        if reserve_port $port; then
+            if port_is_free $port $address $protocol; then
+                echo $port
+                return
+            fi
+
+            unreserve_port $port
         fi
     done
 
@@ -308,8 +343,13 @@ function random_free_port_range() {
         local lastport=
         for i in $(seq 1 $((size - 1))); do
             lastport=$((firstport + i))
+            if ! reserve_port $lastport; then
+                lastport=
+                break
+            fi
             if ! port_is_free $lastport $address $protocol; then
                 echo "# port $lastport is in use; trying another." >&3
+                unreserve_port $lastport
                 lastport=
                 break
             fi
@@ -319,6 +359,8 @@ function random_free_port_range() {
             return
         fi
 
+        unreserve_port $firstport
+
         maxtries=$((maxtries - 1))
     done
 

test/system/helpers.t

@@ -22,6 +22,9 @@ rc=0
 PODMAN_TMPDIR=$(mktemp -d --tmpdir=${TMPDIR:-/tmp} podman_helper_tests.XXXXXX)
 trap 'rm -rf $PODMAN_TMPDIR' 0
 
+# Used by random_free_port.
+PORT_LOCK_DIR=$PODMAN_TMPDIR/reserved-ports
+
 ###############################################################################
 # BEGIN test the parse_table helper