Load app from sdcard on K210, but panicked on qemu.

os/src/syscall/fs.rs

@@ -10,6 +10,9 @@ pub fn sys_write(fd: usize, buf: *const u8, len: usize) -> isize {
         return -1;
     }
     if let Some(file) = &inner.fd_table[fd] {
+        if !file.writable() {
+            return -1;
+        }
         let file = file.clone();
         // release Task lock manually to avoid deadlock
         drop(inner);
@@ -30,6 +33,9 @@ pub fn sys_read(fd: usize, buf: *const u8, len: usize) -> isize {
     }
     if let Some(file) = &inner.fd_table[fd] {
         let file = file.clone();
+        if !file.readable() {
+            return -1;
+        }
         // release Task lock manually to avoid deadlock
         drop(inner);
         file.read(

os/src/syscall/process.rs

@@ -10,7 +10,11 @@ use crate::mm::{
     translated_str,
     translated_refmut,
 };
-use crate::loader::get_app_data_by_name;
+use crate::fs::{
+    OSInode,
+    open_file,
+    OpenFlags,
+};
 use alloc::sync::Arc;
 
 pub fn sys_exit(exit_code: i32) -> ! {
@@ -48,9 +52,10 @@ pub fn sys_fork() -> isize {
 pub fn sys_exec(path: *const u8) -> isize {
     let token = current_user_token();
     let path = translated_str(token, path);
-    if let Some(data) = get_app_data_by_name(path.as_str()) {
+    if let Some(app_inode) = open_file(path.as_str(), OpenFlags::RDONLY) {
+        let all_data = app_inode.read_all();
         let task = current_task().unwrap();
-        task.exec(data);
+        task.exec(all_data.as_slice());
         0
     } else {
         -1