fix:ch6 running ch5_spawn0, by moving buffer to heap

Author: scPointer

Diff for: os/src/fs/inode.rs

@@ -40,7 +40,8 @@ impl OSInode {
     /// read all data from the inode
     pub fn read_all(&self) -> Vec<u8> {
         let mut inner = self.inner.exclusive_access();
-        let mut buffer = [0u8; 512];
+        let mut buffer: Vec<u8> = Vec::with_capacity(512);
+        buffer.resize(512, 0);
         let mut v: Vec<u8> = Vec::new();
         loop {
             let len = inner.inode.read_at(inner.offset, &mut buffer);