pkg/config: make EditConnectionConfig race free

Add a lock to EditConnectionConfig to make it race free for parallel
modification. It is possible that several podman system connection
commands are called simultaneously so we should read/file in a
consistent way to ensure no modifications are "silently dropped".

A test is added that reliably fails without the lock.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

common/pkg/config/connections.go

@@ -9,6 +9,7 @@ import (
 	"path/filepath"
 
 	"github.com/containers/storage/pkg/ioutils"
+	"github.com/containers/storage/pkg/lockfile"
 )
 
 const connectionsFile = "podman-connections.json"
@@ -113,6 +114,15 @@ func EditConnectionConfig(callback func(cfg *ConnectionsFile) error) error {
 	if err != nil {
 		return err
 	}
+
+	lockPath := path + ".lock"
+	lock, err := lockfile.GetLockFile(lockPath)
+	if err != nil {
+		return fmt.Errorf("obtain lock file: %w", err)
+	}
+	lock.Lock()
+	defer lock.Unlock()
+
 	conf, err := readConnectionConf(path)
 	if err != nil {
 		return fmt.Errorf("read connections file: %w", err)

common/pkg/config/connections_test.go

@@ -3,6 +3,8 @@ package config
 import (
 	"os"
 	"path/filepath"
+	"strconv"
+	"sync"
 
 	. "github.com/onsi/ginkgo/v2"
 	"github.com/onsi/gomega"
@@ -73,6 +75,43 @@ var _ = Describe("Connections conf", func() {
 		gomega.Expect(conf).To(gomega.Equal(orgConf))
 	})
 
+	It("parallel EditConnectionConfig", func() {
+		// race test for EditConnectionConfig
+		// Basic idea spawn a bunch of goroutines and call EditConnectionConfig at the same time.
+		// We read a int from one field and then +1 one it each time so at the end we must have
+		// the number in the filed for how many times we called EditConnectionConfig. If it is
+		// less than it is racy.
+		count := 50
+		wg := sync.WaitGroup{}
+		wg.Add(count)
+		for i := 0; i < count; i++ {
+			go func() {
+				defer wg.Done()
+				err := EditConnectionConfig(func(cfg *ConnectionsFile) error {
+					if cfg.Connection.Default == "" {
+						cfg.Connection.Default = "1"
+						return nil
+					}
+					// basic idea just add 1
+					i, err := strconv.Atoi(cfg.Connection.Default)
+					if err != nil {
+						return err
+					}
+					i++
+					cfg.Connection.Default = strconv.Itoa(i)
+					return nil
+				})
+				gomega.Expect(err).ToNot(gomega.HaveOccurred())
+			}()
+		}
+		wg.Wait()
+		path, err := connectionsConfigFile()
+		gomega.Expect(err).ToNot(gomega.HaveOccurred())
+		conf, err := readConnectionConf(path)
+		gomega.Expect(err).ToNot(gomega.HaveOccurred())
+		gomega.Expect(conf.Connection.Default).To(gomega.Equal("50"))
+	})
+
 	Context("GetConnection/Farm", func() {
 		const defConnectionsConf = `{"Connection":{"Default":"test","Connections":{"test":{"URI":"ssh://podman.io"},"QA":{"URI":"ssh://test","Identity":".ssh/id","IsMachine":true}}},"farm":{"Default":"farm1","List":{"farm1":["test"]}}}`
 		const defContainersConf = `