nydus-rs 2.1.0-alpha2

diff --git a/src/bin/nydusd/main.rs b/src/bin/nydusd/main.rs
index e0ee57d8..c9b41fc5 100644
--- a/src/bin/nydusd/main.rs
+++ b/src/bin/nydusd/main.rs
@@ -196,11 +196,12 @@ extern "C" fn sig_exit(_sig: std::os::raw::c_int) {
 }
 
 #[cfg(feature = "virtiofs")]
-const SHARED_DIR_HELP_MESSAGE: &str = "Directory to share between host and guest by virtiofs, which also enables `passthroughfs` mode";
+const SHARED_DIR_HELP_MESSAGE: &str = "Directory shared by host and guest for \
+passthroughfs, which also enables passthroughfs mode";
 
 #[cfg(feature = "fusedev")]
-const SHARED_DIR_HELP_MESSAGE: &str =
-    "Directory to share by FUSE for testing, which also enables `passthroughfs` mode";
+const SHARED_DIR_HELP_MESSAGE: &str = "A passthroughfs source for FUSE (the \
+purpose of testing and demonstration), which also enables passthroughfs mode";
 
 #[cfg(any(feature = "fusedev", feature = "virtiofs"))]
 fn append_fs_options(app: App<'static, 'static>) -> App<'static, 'static> {
@@ -208,7 +209,7 @@ fn append_fs_options(app: App<'static, 'static>) -> App<'static, 'static> {
         Arg::with_name("bootstrap")
             .long("bootstrap")
             .short("B")
-            .help("Bootstrap file of a rafs filesystem, which also enables `rafs` mode")
+            .help("Bootstrap/metadata file for rafs filesystem, which also enables rafs mode")
             .takes_value(true)
             .requires("config")
             .conflicts_with("shared-dir"),
@@ -235,7 +236,7 @@ fn append_fs_options(app: App<'static, 'static>) -> App<'static, 'static> {
         Arg::with_name("virtual-mountpoint")
             .long("virtual-mountpoint")
             .short("m")
-            .help("Path within the FUSE/virtiofs device to mount the filesystem")
+            .help("Path inside FUSE/virtiofs virtual filesystem to mount the rafs/passthroughfs instance")
             .takes_value(true)
             .default_value("/")
             .required(false),
@@ -267,7 +268,7 @@ fn append_fuse_options(app: App<'static, 'static>) -> App<'static, 'static> {
             .long("thread-num")
             .short("T")
             .default_value("1")
-            .help("Number of worker threads to serve IO requests")
+            .help("Number of working threads to serve FUSE IO requests")
             .takes_value(true)
             .required(false)
             .validator(|v| {
@@ -286,7 +287,7 @@ fn append_fuse_options(app: App<'static, 'static>) -> App<'static, 'static> {
         Arg::with_name("writable")
             .long("writable")
             .short("W")
-            .help("Mounts FUSE filesystem in rw mode")
+            .help("Mount FUSE filesystem in rw mode")
             .takes_value(false),
     )
 }
@@ -305,7 +306,7 @@ fn append_virtiofs_options(app: App<'static, 'static>) -> App<'static, 'static>
         Arg::with_name("hybrid-mode")
             .long("hybrid-mode")
             .short("H")
-            .help("Enables both `rafs` and `passthroughfs` modes")
+            .help("Enable support for both rafs and passthroughfs modes")
             .required(false)
             .takes_value(false),
     )
@@ -334,13 +335,13 @@ fn append_services_subcmd_options(app: App<'static, 'static>) -> App<'static, 's
             Arg::with_name("fscache")
                 .long("fscache")
                 .short("F")
-                .help("Working directory for Linux fscache driver to store cached files")
+                .help("Working directory fscache driver to cache files")
                 .takes_value(true),
         )
         .arg(
             Arg::with_name("fscache-tag")
                 .long("fscache-tag")
-                .help("Tag to identify the fscache daemon instance")
+                .help("Fscache tag to identify the fs daemon instance")
                 .takes_value(true)
                 .requires("fscache"),
         );
@@ -423,7 +424,7 @@ fn prepare_commandline_options() -> App<'static, 'static> {
             Arg::with_name("upgrade")
                 .long("upgrade")
                 .short("U")
-                .help("Starts daemon in upgrade mode")
+                .help("Start in upgrade mode")
                 .takes_value(false)
                 .required(false)
                 .global(true),
@@ -546,7 +547,6 @@ impl<'a> SubCmdArgs<'a> {
     }
 }
 
-#[cfg(any(feature = "fusedev", feature = "virtiofs"))]
 fn process_default_fs_service(
     args: SubCmdArgs,
     bti: BuildTimeInfo,
@@ -676,18 +676,6 @@ fn process_default_fs_service(
     Ok(())
 }
 
-#[cfg(not(any(feature = "fusedev", feature = "virtiofs")))]
-fn process_default_fs_service(
-    _args: SubCmdArgs,
-    _bti: BuildTimeInfo,
-    _apisock: Option<&str>,
-    _is_fuse: bool,
-) -> Result<()> {
-    return Err(einval!(
-        "Neither fusedev nor virtiofs is enabled, please recompile nydusd with required features!"
-    ));
-}
-
 fn process_daemon_arguments(
     subargs: &SubCmdArgs,
     _apisock: Option<&str>,
@@ -710,6 +698,7 @@ fn main() -> Result<()> {
 
     setup_logging(logging_file, level)?;
     dump_program_info(crate_version!());
+    handle_rlimit_nofile_option(&args, "rlimit-nofile")?;
 
     match args.subcommand_name() {
         Some("daemon") => {
@@ -736,13 +725,9 @@ fn main() -> Result<()> {
             process_default_fs_service(subargs, bti, apisock, true)?;
             #[cfg(feature = "virtiofs")]
             process_default_fs_service(subargs, bti, apisock, false)?;
-            #[cfg(not(any(feature = "fusedev", feature = "virtiofs")))]
-            process_default_fs_service(subargs, bti, apisock, false)?;
         }
     }
 
-    handle_rlimit_nofile_option(&args, "rlimit-nofile")?;
-
     let daemon = DAEMON_CONTROLLER.get_daemon();
     if let Some(fs) = daemon.get_default_fs_service() {
         DAEMON_CONTROLLER.set_fs_service(fs);