blob save fsync feature flag (#13652)

Co-authored-by: Kasey Kirkham <kasey@users.noreply.github.com>

config/features/config.go

@@ -69,7 +69,8 @@ type Flags struct {
 	EnableEIP4881                bool // EnableEIP4881 specifies whether to use the deposit tree from EIP4881
 
 	PrepareAllPayloads bool // PrepareAllPayloads informs the engine to prepare a block on every slot.
-
+	// BlobSaveFsync requires blob saving to block on fsync to ensure blobs are durably persisted before passing DA.
+	BlobSaveFsync bool
 	// KeystoreImportDebounceInterval specifies the time duration the validator waits to reload new keys if they have
 	// changed on disk. This feature is for advanced use cases only.
 	KeystoreImportDebounceInterval time.Duration
@@ -245,6 +246,11 @@ func ConfigureBeaconChain(ctx *cli.Context) error {
 		logEnabled(EnableLightClient)
 		cfg.EnableLightClient = true
 	}
+	if ctx.IsSet(BlobSaveFsync.Name) {
+		logEnabled(BlobSaveFsync)
+		cfg.BlobSaveFsync = true
+	}
+
 	cfg.AggregateIntervals = [3]time.Duration{aggregateFirstInterval.Value, aggregateSecondInterval.Value, aggregateThirdInterval.Value}
 	Init(cfg)
 	return nil

config/features/flags.go

@@ -149,12 +149,16 @@ var (
 		Name:  "disable-resource-manager",
 		Usage: "Disables running the libp2p resource manager.",
 	}
-
 	// DisableRegistrationCache a flag for disabling the validator registration cache and use db instead.
 	DisableRegistrationCache = &cli.BoolFlag{
 		Name:  "disable-registration-cache",
 		Usage: "Temporary flag for disabling the validator registration cache instead of using the DB. Note: registrations do not clear on restart while using the DB.",
 	}
+	// BlobSaveFsync enforces durable filesystem writes for use cases where blob availability is critical.
+	BlobSaveFsync = &cli.BoolFlag{
+		Name:  "blob-save-fsync",
+		Usage: "Forces new blob files to be fysnc'd before continuing, ensuring durable blob writes.",
+	}
 )
 
 // devModeFlags holds list of flags that are set when development mode is on.
@@ -209,6 +213,7 @@ var BeaconChainFlags = append(deprecatedBeaconFlags, append(deprecatedFlags, []c
 	disableResourceManager,
 	DisableRegistrationCache,
 	EnableLightClient,
+	BlobSaveFsync,
 }...)...)
 
 // E2EBeaconChainFlags contains a list of the beacon chain feature flags to be tested in E2E.