Minor optimizations on both lat-syscall-stat and lat-syscall-open

kernel/src/context.rs

@@ -191,7 +191,7 @@ impl<'a> ReadCString for VmReader<'a, Fallible> {
 
         // Handle the first few bytes to make `cur_addr` aligned with `size_of::<usize>`
         read_one_byte_at_a_time_while!(
-            (self.cursor() as usize) % mem::size_of::<usize>() != 0 && buffer.len() < max_len
+            !is_addr_aligned(self.cursor() as usize) && buffer.len() < max_len
         );
 
         // Handle the rest of the bytes in bulk
@@ -253,3 +253,8 @@ fn check_vaddr(va: Vaddr) -> Result<()> {
         Ok(())
     }
 }
+
+/// Checks if the given address is aligned.
+const fn is_addr_aligned(addr: usize) -> bool {
+    (addr & (mem::size_of::<usize>() - 1)) == 0
+}

kernel/src/fs/fs_resolver.rs

@@ -187,6 +187,7 @@ impl FsResolver {
     /// If `follow_tail_link` is true and the trailing component is a symlink,
     /// it will be followed.
     /// Symlinks in earlier components of the path will always be followed.
+    #[allow(clippy::redundant_closure)]
     fn lookup_from_parent(
         &self,
         parent: &Arc<Dentry>,
@@ -205,7 +206,7 @@ impl FsResolver {
 
         // To handle symlinks
         let follow_tail_link = lookup_ctx.follow_tail_link;
-        let mut link_path = String::new();
+        let mut link_path_opt = None;
         let mut follows = 0;
 
         // Initialize the first dentry and the relative path
@@ -263,9 +264,10 @@ impl FsResolver {
                 if link_path_remain.starts_with('/') {
                     dentry = self.root.clone();
                 }
+                let link_path = link_path_opt.get_or_insert_with(|| String::new());
                 link_path.clear();
                 link_path.push_str(link_path_remain.trim_start_matches('/'));
-                relative_path = &link_path;
+                relative_path = link_path;
                 follows += 1;
             } else {
                 // If path ends with `/`, the inode must be a directory

kernel/src/fs/inode_handle/dyn_cap.rs

@@ -12,11 +12,11 @@ impl InodeHandle<Rights> {
         access_mode: AccessMode,
         status_flags: StatusFlags,
     ) -> Result<Self> {
-        let inode = dentry.inode();
-        if access_mode.is_readable() && !inode.mode()?.is_readable() {
+        let inode_mode = dentry.inode().mode()?;
+        if access_mode.is_readable() && !inode_mode.is_readable() {
             return_errno_with_message!(Errno::EACCES, "file is not readable");
         }
-        if access_mode.is_writable() && !inode.mode()?.is_writable() {
+        if access_mode.is_writable() && !inode_mode.is_writable() {
             return_errno_with_message!(Errno::EACCES, "file is not writable");
         }
 
@@ -29,7 +29,7 @@ impl InodeHandle<Rights> {
         status_flags: StatusFlags,
     ) -> Result<Self> {
         let inode = dentry.inode();
-        if access_mode.is_writable() && inode.type_() == InodeType::Dir {
+        if inode.type_() == InodeType::Dir && access_mode.is_writable() {
             return_errno_with_message!(Errno::EISDIR, "directory cannot open to write");
         }
 

kernel/src/fs/ramfs/fs.rs

@@ -68,10 +68,6 @@ impl RamFS {
     fn alloc_id(&self) -> u64 {
         self.inode_allocator.fetch_add(1, Ordering::SeqCst)
     }
-
-    fn device_id(&self) -> u64 {
-        0
-    }
 }
 
 impl FileSystem for RamFS {
@@ -783,6 +779,9 @@ impl Inode for RamInode {
     }
 
     fn as_device(&self) -> Option<Arc<dyn Device>> {
+        if !self.typ.is_device() {
+            return None;
+        }
         self.node.read().inner.as_device().cloned()
     }
 
@@ -1146,20 +1145,21 @@ impl Inode for RamInode {
 
     fn metadata(&self) -> Metadata {
         let self_inode = self.node.read();
+        let inode_metadata = &self_inode.metadata;
         Metadata {
-            dev: self.fs.upgrade().unwrap().device_id(),
+            dev: 0,
             ino: self.ino as _,
-            size: self_inode.metadata.size,
+            size: inode_metadata.size,
             blk_size: BLOCK_SIZE,
-            blocks: self_inode.metadata.blocks,
-            atime: self_inode.metadata.atime,
-            mtime: self_inode.metadata.mtime,
-            ctime: self_inode.metadata.ctime,
+            blocks: inode_metadata.blocks,
+            atime: inode_metadata.atime,
+            mtime: inode_metadata.mtime,
+            ctime: inode_metadata.ctime,
             type_: self.typ,
-            mode: self_inode.metadata.mode,
-            nlinks: self_inode.metadata.nlinks,
-            uid: self_inode.metadata.uid,
-            gid: self_inode.metadata.gid,
+            mode: inode_metadata.mode,
+            nlinks: inode_metadata.nlinks,
+            uid: inode_metadata.uid,
+            gid: inode_metadata.gid,
             rdev: {
                 if let Some(device) = self_inode.inner.as_device() {
                     device.id().into()

test/benchmark/lmbench/vfs_open_lat/run.sh

@@ -6,5 +6,5 @@ set -e
 
 echo "*** Running the LMbench open latency test ***"
 
-touch test_file
-/benchmark/bin/lmbench/lat_syscall -P 1 open test_file
+touch testfile
+/benchmark/bin/lmbench/lat_syscall -P 1 -W 1000 -N 1000 open testfile

test/benchmark/lmbench/vfs_stat_lat/run.sh

@@ -6,5 +6,5 @@ set -e
 
 echo "*** Running the LMbench stat latency test ***"
 
-touch test_file
-/benchmark/bin/lmbench/lat_syscall -P 1 stat test_file
+touch testfile
+/benchmark/bin/lmbench/lat_syscall -P 1 -W 1000 -N 1000 stat testfile