flexnbd status: Add the size of the backing file, in bytes

This will be handy information if you're querying flexnbd for migration
stats, particularly.

src/status.c

@@ -9,6 +9,7 @@ struct status * status_create( struct server * serve )
 
 	status = xmalloc( sizeof( struct status ) );
 	status->pid = getpid();
+	status->size = serve->size;
 	status->has_control = serve->success;
 	status->is_mirroring = NULL != serve->mirror;
 
@@ -25,10 +26,13 @@ struct status * status_create( struct server * serve )
 	do{dprintf( fd, #var "=%s ", BOOL_S( status->var ) );}while(0)
 #define PRINT_INT( var ) \
 	do{dprintf( fd, #var "=%d ", status->var );}while(0)
+#define PRINT_UINT64( var ) \
+	do{dprintf( fd, #var "=%"PRIu64" ", status->var );}while(0)
 
 int status_write( struct status * status, int fd )
 {
 	PRINT_INT( pid );
+	PRINT_UINT64( size );
 	PRINT_BOOL( is_mirroring );
 	PRINT_BOOL( has_control );
 

src/status.h

@@ -20,6 +20,9 @@
  * pid:
  *      The current process ID.
  *
+ * size:
+ *  The size of the backing file being served, in bytes.
+ *
  * has_control:
  * 	This will be false when the server is listening for an incoming
  * 	migration.  It will switch to true when the end-of-migration
@@ -53,6 +56,7 @@
 
 struct status {
 	pid_t pid;
+	uint64_t size;
 	int has_control;
 	int is_mirroring;
 	int migration_pass;