sqlite: move first read into a transaction

According to an old upstream issue [1]: "If the first statement after
BEGIN DEFERRED is a SELECT, then a read transaction is started.
Subsequent write statements will upgrade the transaction to a write
transaction if possible, or return SQLITE_BUSY."

So let's move the first SELECT under the same transaction as the table
initialization.

[NO NEW TESTS NEEDED] as it's a hard to cause race.

[1] mattn/go-sqlite3#274 (comment)

Fixes: containers#17859
Signed-off-by: Valentin Rothberg <[email protected]>

libpod/sqlite_state.go

@@ -78,18 +78,11 @@ func NewSqliteState(runtime *Runtime) (_ State, defErr error) {
  }
  }()
 
- state.conn = conn
-
- // Migrate schema (if necessary)
- if err := state.migrateSchemaIfNecessary(); err != nil {
+ if err := initSQLiteDB(conn); err != nil {
  return nil, err
  }
 
- // Set up tables
- if err := sqliteInitTables(state.conn); err != nil {
- return nil, fmt.Errorf("creating tables: %w", err)
- }
-
+ state.conn = conn
  state.valid = true
  state.runtime = runtime
 

libpod/sqlite_state_internal.go

@@ -15,52 +15,85 @@ import (
  _ "github.com/mattn/go-sqlite3"
 )
 
-func (s *SQLiteState) migrateSchemaIfNecessary() (defErr error) {
+func initSQLiteDB(conn *sql.DB) (defErr error) {
+ // Start with a transaction to avoid "database locked" errors.
+ // See https:/mattn/go-sqlite3/issues/274#issuecomment-1429054597
+ tx, err := conn.Begin()
+ if err != nil {
+ return fmt.Errorf("beginning transaction: %w", err)
+ }
+ defer func() {
+ if defErr != nil {
+ if err := tx.Rollback(); err != nil {
+ logrus.Errorf("Rolling back transaction to create tables: %v", err)
+ }
+ }
+ }()
+
+ sameSchema, err := migrateSchemaIfNecessary(tx)
+ if err != nil {
+ return err
+ }
+ if !sameSchema {
+ if err := createSQLiteTables(tx); err != nil {
+ return err
+ }
+ }
+ if err := tx.Commit(); err != nil {
+ return fmt.Errorf("committing transaction: %w", err)
+ }
+ return nil
+}
+
+func migrateSchemaIfNecessary(tx *sql.Tx) (bool, error) {
  // First, check if the DBConfig table exists
- checkRow := s.conn.QueryRow("SELECT 1 FROM sqlite_master WHERE type='table' AND name='DBConfig';")
+ checkRow := tx.QueryRow("SELECT 1 FROM sqlite_master WHERE type='table' AND name='DBConfig';")
  var check int
  if err := checkRow.Scan(&check); err != nil {
  if errors.Is(err, sql.ErrNoRows) {
- return nil
+ return false, nil
  }
- return fmt.Errorf("checking if DB config table exists: %w", err)
+ return false, fmt.Errorf("checking if DB config table exists: %w", err)
  }
  if check != 1 {
  // Table does not exist, fresh database, no need to migrate.
- return nil
+ return false, nil
  }
 
- row := s.conn.QueryRow("SELECT SchemaVersion FROM DBConfig;")
+ row := tx.QueryRow("SELECT SchemaVersion FROM DBConfig;")
  var schemaVer int
  if err := row.Scan(&schemaVer); err != nil {
  if errors.Is(err, sql.ErrNoRows) {
  // Brand-new, unpopulated DB.
  // Schema was just created, so it has to be the latest.
- return nil
+ return false, nil
  }
- return fmt.Errorf("scanning schema version from DB config: %w", err)
+ return false, fmt.Errorf("scanning schema version from DB config: %w", err)
  }
 
  // If the schema version 0 or less, it's invalid
  if schemaVer <= 0 {
- return fmt.Errorf("database schema version %d is invalid: %w", schemaVer, define.ErrInternal)
+ return false, fmt.Errorf("database schema version %d is invalid: %w", schemaVer, define.ErrInternal)
  }
 
- if schemaVer != schemaVersion {
- // If the DB is a later schema than we support, we have to error
- if schemaVer > schemaVersion {
- return fmt.Errorf("database has schema version %d while this libpod version only supports version %d: %w",
- schemaVer, schemaVersion, define.ErrInternal)
- }
+ // Same schema -> nothing do to.
+ if schemaVer == schemaVersion {
+ return true, nil
+ }
 
- // Perform schema migration here, one version at a time.
+ // If the DB is a later schema than we support, we have to error
+ if schemaVer > schemaVersion {
+ return false, fmt.Errorf("database has schema version %d while this libpod version only supports version %d: %w",
+ schemaVer, schemaVersion, define.ErrInternal)
  }
 
- return nil
+ // Perform schema migration here, one version at a time.
+
+ return false, nil
 }
 
 // Initialize all required tables for the SQLite state
-func sqliteInitTables(conn *sql.DB) (defErr error) {
+func createSQLiteTables(tx *sql.Tx) error {
  // Technically we could split the "CREATE TABLE IF NOT EXISTS" and ");"
  // bits off each command and add them in the for loop where we actually
  // run the SQL, but that seems unnecessary.
@@ -186,28 +219,11 @@ func sqliteInitTables(conn *sql.DB) (defErr error) {
  "VolumeState": volumeState,
  }
 
- tx, err := conn.Begin()
- if err != nil {
- return fmt.Errorf("beginning transaction: %w", err)
- }
- defer func() {
- if defErr != nil {
- if err := tx.Rollback(); err != nil {
- logrus.Errorf("Rolling back transaction to create tables: %v", err)
- }
- }
- }()
-
  for tblName, cmd := range tables {
  if _, err := tx.Exec(cmd); err != nil {
  return fmt.Errorf("creating table %s: %w", tblName, err)
  }
  }
-
- if err := tx.Commit(); err != nil {
- return fmt.Errorf("committing transaction: %w", err)
- }
-
  return nil
 }