Metadata-prefetch (aka Recursive listing or ls -R during mount)

flags.go

@@ -34,6 +34,10 @@ import (
 const (
 	// maxSequentialReadSizeMb is the max value supported by sequential-read-size-mb flag.
 	maxSequentialReadSizeMb = 1024
+
+	// MetadataPrefetchOnMountFlag is the name of the commandline flag for enabling
+	// metadata-prefetch mode aka 'ls -R' during mount.
+	MetadataPrefetchOnMountFlag = "metadata-prefetch-on-mount"
 )
 
 // Set up custom help text for gcsfuse; in particular the usage section.
@@ -360,6 +364,16 @@ func newApp() (app *cli.App) {
 				Name:  "debug_mutex",
 				Usage: "Print debug messages when a mutex is held too long.",
 			},
+
+			/////////////////////////
+			// Post-mount actions
+			/////////////////////////
+
+			cli.StringFlag{
+				Name:  MetadataPrefetchOnMountFlag,
+				Value: config.DefaultMetadataPrefetchOnMount,
+				Usage: "This indicates whether or not to prefetch the metadata (prefilling of metadata caches and creation of inodes) of the mounted bucket at the time of mounting the bucket. Supported values: \"disabled\", \"sync\" and \"async\". Any other values will return error on mounting. This is applicable only to single-bucket mount-points, and not to dynamic-mount points.",
+			},
 		},
 	}
 
@@ -423,6 +437,15 @@ type flagStorage struct {
 	DebugHTTP       bool
 	DebugInvariants bool
 	DebugMutex      bool
+
+	// Post-mount actions
+
+	// MetadataPrefetchOnMount indicates whether or not to prefetch the metadata of the mounted bucket at the time of mounting the bucket.
+	// Supported values: MetadataPrefetchOnMountDisabled, MetadataPrefetchOnMountSynchronous, and MetadataPrefetchOnMountAsynchronous.
+	// Any other values will return error on mounting.
+	// This is applicable only to single-bucket mount-points, and not to dynamic-mount points. This is because dynamic-mounts don't mount the bucket(s) at the time of
+	// gcsfuse command itself, which flag is targeted at.
+	MetadataPrefetchOnMount string
 }
 
 func resolveFilePath(filePath string, configKey string) (resolvedPath string, err error) {
@@ -563,6 +586,9 @@ func populateFlags(c *cli.Context) (flags *flagStorage, err error) {
 		DebugFS:         c.Bool("debug_fs"),
 		DebugInvariants: c.Bool("debug_invariants"),
 		DebugMutex:      c.Bool("debug_mutex"),
+
+		// Post-mount actions
+		MetadataPrefetchOnMount: c.String(MetadataPrefetchOnMountFlag),
 	}
 
 	// Handle the repeated "-o" flag.
@@ -575,17 +601,33 @@ func populateFlags(c *cli.Context) (flags *flagStorage, err error) {
 	return
 }
 
+func validateMetadataPrefetchOnMount(mode string) error {
+	switch mode {
+	case config.MetadataPrefetchOnMountDisabled:
+		fallthrough
+	case config.MetadataPrefetchOnMountSynchronous:
+		fallthrough
+	case config.MetadataPrefetchOnMountAsynchronous:
+		return nil
+	default:
+		return fmt.Errorf(config.UnsupportedMetadataPrefixModeError, mode)
+	}
+}
+
 func validateFlags(flags *flagStorage) (err error) {
 	if flags.SequentialReadSizeMb < 1 || flags.SequentialReadSizeMb > maxSequentialReadSizeMb {
-		err = fmt.Errorf("SequentialReadSizeMb should be less than %d", maxSequentialReadSizeMb)
-		return
+		return fmt.Errorf("SequentialReadSizeMb should be less than %d", maxSequentialReadSizeMb)
 	}
 
 	if !flags.ClientProtocol.IsValid() {
-		err = fmt.Errorf("client protocol: %s is not valid", flags.ClientProtocol)
+		return fmt.Errorf("client protocol: %s is not valid", flags.ClientProtocol)
 	}
 
-	return
+	if err = validateMetadataPrefetchOnMount(flags.MetadataPrefetchOnMount); err != nil {
+		return fmt.Errorf("%s: is not valid; error = %w", MetadataPrefetchOnMountFlag, err)
+	}
+
+	return nil
 }
 
 // A cli.Generic that can be used with cli.GenericFlag to obtain an int flag