init: Adopt opendir() and readdir() syscalls

Use opendir() and readdir() for dm discovery. Currently, it naively runs
the first file discovered under /bin.

Co-developed-by: Vijay Dhanraj <[email protected]>
Signed-off-by: Peter Fang <[email protected]>

init/src/main.rs

@@ -9,9 +9,11 @@
 
 extern crate alloc;
 use alloc::ffi::CString;
+use alloc::string::String;
 use buddy_system_allocator::*;
+use core::ffi::CStr;
 use core::panic::PanicInfo;
-use syscall::{exec, exit, SysCallError};
+use syscall::{exec, exit, opendir, readdir, DirEnt, SysCallError, F_TYPE_FILE};
 
 const HEAP_SIZE: usize = 64 * 1024;
 static mut HEAP: [u8; HEAP_SIZE] = [0; HEAP_SIZE];
@@ -27,13 +29,39 @@ pub extern "C" fn init_start() -> ! {
             .init(core::ptr::addr_of!(HEAP) as usize, HEAP_SIZE);
     }
 
-    let file = CString::new("/dummy").expect("Failed to create new string");
-    let root = CString::new("/").expect("Failed to create new string");
+    let bin = CString::new("/bin/").unwrap();
+    let Ok(obj) = opendir(&bin) else {
+        exit(0);
+    };
+    let mut dirents: [DirEnt; 8] = Default::default();
+    let mut binfile: Option<CString> = None;
+
+    'outer: loop {
+        let n = readdir(&obj, &mut dirents).unwrap();
+        for d in dirents.iter().take(n) {
+            if d.file_type == F_TYPE_FILE {
+                binfile = Some(CString::from(
+                    CStr::from_bytes_until_nul(&d.file_name).unwrap(),
+                ));
+                break 'outer;
+            }
+        }
+        if n < dirents.len() {
+            break;
+        }
+    }
+    let binfile = binfile.unwrap_or_else(|| exit(0));
+
+    let mut file = String::from(bin.as_c_str().to_str().unwrap());
+    file.push_str(binfile.as_c_str().to_str().unwrap());
+
+    let file = CString::new(file).unwrap();
+    let root = CString::new("/").unwrap();
 
     match exec(&file, &root, 0) {
         Ok(_) => exit(0),
         Err(SysCallError::ENOTFOUND) => exit(1),
-        _ => panic!("exec launch failed"),
+        _ => panic!("{} launch failed", file.to_str().unwrap()),
     };
 }