Support to execute a symlink file

deps/sefs

@@ -1 +1 @@
-Subproject commit b3565f22b547dac487b46a1fb4d6c8c5d1b3162e
+Subproject commit 1d173f103626d4771e120456f8960a7ff3157583

src/libos/src/fs/fs_view.rs

@@ -80,16 +80,37 @@ impl FsView {
 
     /// Lookup INode from the cwd of the process
     pub fn lookup_inode(&self, path: &str) -> Result<Arc<dyn INode>> {
-        debug!("lookup_inode: cwd: {:?}, path: {:?}", self.cwd(), path);
+        self.lookup_inode_follow_with_max_times(path, 0)
+    }
+
+    /// Lookup INode from the cwd of the process, follow symlinks
+    pub fn lookup_inode_follow(&self, path: &str) -> Result<Arc<dyn INode>> {
+        // Linux uses 40 as the upper limit for resolving symbolic links,
+        // so Occlum use it as a reasonable value
+        const MAX_SYMLINKS: usize = 40;
+        self.lookup_inode_follow_with_max_times(path, MAX_SYMLINKS)
+    }
+
+    fn lookup_inode_follow_with_max_times(
+        &self,
+        path: &str,
+        max_times: usize,
+    ) -> Result<Arc<dyn INode>> {
+        debug!(
+            "lookup_inode_follow_with_max_times: cwd: {:?}, path: {:?}, max_times: {}",
+            self.cwd(),
+            path,
+            max_times
+        );
         if path.len() > 0 && path.as_bytes()[0] == b'/' {
             // absolute path
             let abs_path = path.trim_start_matches('/');
-            let inode = ROOT_INODE.lookup(abs_path)?;
+            let inode = ROOT_INODE.lookup_follow(abs_path, max_times)?;
             Ok(inode)
         } else {
             // relative path
             let cwd = self.cwd().trim_start_matches('/');
-            let inode = ROOT_INODE.lookup(cwd)?.lookup(path)?;
+            let inode = ROOT_INODE.lookup(cwd)?.lookup_follow(path, max_times)?;
             Ok(inode)
         }
     }

src/libos/src/process/do_spawn/mod.rs

@@ -206,7 +206,7 @@ fn load_elf_to_vec(elf_path: &str, current_ref: &ThreadRef) -> Result<Vec<u8>> {
         .fs()
         .lock()
         .unwrap()
-        .lookup_inode(elf_path)
+        .lookup_inode_follow(elf_path)
         .map_err(|e| errno!(e.errno(), "cannot find the ELF"))?;
     let file_mode = {
         let info = inode.metadata()?;