containers.conf: add database backend option

The on-going work of adding a new database backend to Podman requires it
to be configurable in containers.conf.  To prevent any breaking changes,
the backend defaults to Podman's current boltdb backend.  Also export
the parsing function for it be usable by Podman.

NOTE: documentation will be added once the database rewrite in Podman
has been completed.  I want to avoid any incomplete docs from leaking
into a release.

Fixes: https://issues.redhat.com/browse/RUN-1772
Signed-off-by: Valentin Rothberg <[email protected]>

pkg/config/config.go

@@ -251,6 +251,9 @@ type EngineConfig struct {
 	// in containers-registries.conf(5).
 	CompatAPIEnforceDockerHub bool `toml:"compat_api_enforce_docker_hub,omitempty"`
 
+	// DBBackend is the database backend to be used by Podman.
+	DBBackend string `toml:"database_backend,omitempty"`
+
 	// DetachKeys is the sequence of keys used to detach a container.
 	DetachKeys string `toml:"detach_keys,omitempty"`
 
@@ -898,6 +901,11 @@ func (c *EngineConfig) Validate() error {
 	if _, err := ValidatePullPolicy(pullPolicy); err != nil {
 		return fmt.Errorf("invalid pull type from containers.conf %q: %w", c.PullPolicy, err)
 	}
+
+	if _, err := ParseDBBackend(c.DBBackend); err != nil {
+		return err
+	}
+
 	return nil
 }
 

pkg/config/config_test.go

@@ -37,6 +37,11 @@ var _ = Describe("Config", func() {
 			gomega.Expect(defaultConfig.Engine.ImageVolumeMode).To(gomega.BeEquivalentTo("bind"))
 			gomega.Expect(defaultConfig.Engine.SSHConfig).To(gomega.ContainSubstring("/.ssh/config"))
 			gomega.Expect(defaultConfig.Engine.EventsContainerCreateInspectData).To(gomega.BeFalse())
+			gomega.Expect(defaultConfig.Engine.DBBackend).To(gomega.BeEquivalentTo(stringBoltDB))
+
+			dbBackend, err := defaultConfig.DBBackend()
+			gomega.Expect(dbBackend).To(gomega.BeEquivalentTo(DBBackendBoltDB))
+			gomega.Expect(err).To(gomega.BeNil())
 			path, err := defaultConfig.ImageCopyTmpDir()
 			gomega.Expect(err).To(gomega.BeNil())
 			gomega.Expect(path).To(gomega.BeEquivalentTo("/var/tmp"))
@@ -410,6 +415,11 @@ image_copy_tmp_dir="storage"`
 			gomega.Expect(config.Containers.HostContainersInternalIP).To(gomega.BeEquivalentTo("1.2.3.4"))
 			gomega.Expect(config.Engine.ImageVolumeMode).To(gomega.BeEquivalentTo("tmpfs"))
 			gomega.Expect(config.Engine.SSHConfig).To(gomega.Equal("/foo/bar/.ssh/config"))
+
+			gomega.Expect(config.Engine.DBBackend).To(gomega.Equal(stringSQLite))
+			dbBackend, err := config.DBBackend()
+			gomega.Expect(err).To(gomega.BeNil())
+			gomega.Expect(dbBackend).To(gomega.BeEquivalentTo(DBBackendSQLite))
 		})
 
 		It("contents of passed-in file should override others", func() {
@@ -553,6 +563,12 @@ image_copy_tmp_dir="storage"`
 			err := sut.Engine.Validate()
 			gomega.Expect(err).ToNot(gomega.BeNil())
 		})
+
+		It("should fail with invalid database_backend", func() {
+			sut.Engine.DBBackend = ""
+			err := sut.Engine.Validate()
+			gomega.Expect(err).ToNot(gomega.BeNil())
+		})
 	})
 
 	Describe("Service Destinations", func() {

pkg/config/db_backend.go

@@ -0,0 +1,60 @@
+package config
+
+import "fmt"
+
+// DBBackend determines which supported database backend Podman should use.
+type DBBackend int
+
+const (
+	// Unsupported database backend.  Used as a sane base value for the type.
+	DBBackendUnsupported DBBackend = iota
+	// BoltDB backend.
+	DBBackendBoltDB
+	// SQLite backend.
+	DBBackendSQLite
+
+	stringBoltDB = "boltdb"
+	stringSQLite = "sqlite"
+)
+
+// String returns the DBBackend's string representation.
+func (d DBBackend) String() string {
+	switch d {
+	case DBBackendBoltDB:
+		return stringBoltDB
+	case DBBackendSQLite:
+		return stringSQLite
+	default:
+		return fmt.Sprintf("unsupported database backend: %d", d)
+	}
+}
+
+// Validate returns whether the DBBackend is supported.
+func (d DBBackend) Validate() error {
+	switch d {
+	case DBBackendBoltDB, DBBackendSQLite:
+		return nil
+	default:
+		return fmt.Errorf("unsupported database backend: %d", d)
+	}
+}
+
+// ParseDBBackend parses the specified string into a DBBackend.
+// An error is return for unsupported backends.
+func ParseDBBackend(raw string) (DBBackend, error) {
+	// NOTE: this function should be used for parsing the user-specified
+	// values on Podman's CLI.
+	switch raw {
+	case stringBoltDB:
+		return DBBackendBoltDB, nil
+	case stringSQLite:
+		return DBBackendSQLite, nil
+	default:
+		return DBBackendUnsupported, fmt.Errorf("unsupported database backend: %q", raw)
+	}
+}
+
+// DBBackend returns the configured database backend.
+func (c *Config) DBBackend() (DBBackend, error) {
+	return ParseDBBackend(c.Engine.DBBackend)
+}

pkg/config/db_backend_test.go

@@ -0,0 +1,33 @@
+package config
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestDBBackend(t *testing.T) {
+	tests := []struct {
+		input    string
+		valid    bool
+		expected DBBackend
+	}{
+		{stringBoltDB, true, DBBackendBoltDB},
+		{stringSQLite, true, DBBackendSQLite},
+		{"", false, DBBackendUnsupported},
+		{stringSQLite + " ", false, DBBackendUnsupported},
+	}
+
+	for _, test := range tests {
+		result, err := ParseDBBackend(test.input)
+		if test.valid {
+			require.NoError(t, err, "should parse %v", test)
+			require.NoError(t, result.Validate(), "should validate %v", test)
+			require.Equal(t, test.expected, result)
+		} else {
+			require.Error(t, err, "should NOT parse %v", test)
+			require.Error(t, result.Validate(), "should NOT validate %v", test)
+			require.Equal(t, test.expected, result)
+		}
+	}
+}

pkg/config/default.go

@@ -104,6 +104,8 @@ const (
 	CgroupfsCgroupsManager = "cgroupfs"
 	// DefaultApparmorProfile  specifies the default apparmor profile for the container.
 	DefaultApparmorProfile = apparmor.Profile
+	// DefaultDBBackend specifies the default database backend to be used by Podman.
+	DefaultDBBackend = DBBackendBoltDB
 	// DefaultHostsFile is the default path to the hosts file.
 	DefaultHostsFile = "/etc/hosts"
 	// SystemdCgroupsManager represents systemd native cgroup manager.
@@ -387,6 +389,7 @@ func defaultConfigFromMemory() (*EngineConfig, error) {
 		"/run/current-system/sw/bin/conmonrs",
 	}
 	c.PullPolicy = DefaultPullPolicy
+	c.DBBackend = stringBoltDB
 	c.RuntimeSupportsJSON = []string{
 		"crun",
 		"runc",

pkg/config/testdata/containers_default.conf

@@ -117,6 +117,8 @@ dns_bind_port = 1153
 # Cgroup management implementation used for the runtime.
 cgroup_manager = "systemd"
 
+database_backend = "sqlite"
+
 # Default transport method for pulling and pushing for images
 image_default_transport = "docker://"