fix clippy lint errors

kernel/rustkernel/src/fs/file.rs

@@ -325,7 +325,7 @@ pub unsafe extern "C" fn filewrite(file: *mut File, addr: u64, num_bytes: i32) -
                 }
             }
             if i == num_bytes {
-                num_bytes as i32
+                num_bytes
             } else {
                 -1
             }

kernel/rustkernel/src/io/pipe.rs

@@ -33,6 +33,7 @@ pub struct Pipe {
     pub is_write_open: i32,
 }
 impl Pipe {
+    #[allow(clippy::new_ret_no_self)]
     pub unsafe fn new(a: *mut *mut File, b: *mut *mut File) -> Result<()> {
         *a = filealloc();
         *b = filealloc();
@@ -66,6 +67,7 @@ impl Pipe {
     /// Unsafely get a reference to `self`.
     ///
     /// `self.lock` must be held beforehand.
+    #[allow(clippy::mut_from_ref)]
     unsafe fn as_mut(&self) -> &mut Self {
         &mut *addr_of!(*self).cast_mut()
     }

kernel/rustkernel/src/syscall.rs

@@ -2,8 +2,8 @@ use crate::{
     arch::riscv::memlayout::QEMU_POWER,
     fs::{
         self,
-        file::{self, File, Inode},
-        log::{self, LogOperation},
+        file::{self, File},
+        log::LogOperation,
         stat::KIND_DIR,
     },
     mem::virtual_memory::{copyin, copyinstr},
@@ -102,15 +102,14 @@ impl Syscall {
             }
             Syscall::Chdir => {
                 let mut path = [0u8; crate::MAXPATH];
-                let mut inode: *mut Inode = null_mut();
-                let mut p = myproc();
+                let p = myproc();
 
                 let _operation = LogOperation::new();
 
                 if argstr(0, addr_of_mut!(path).cast(), path.len() as i32) < 0 {
                     return -1i64 as u64;
                 }
-                inode = fs::namei(addr_of_mut!(path).cast());
+                let inode = fs::namei(addr_of_mut!(path).cast());
                 if inode.is_null() {
                     return -1i64 as u64;
                 }