diff --git a/components/dfs/src/dfs_file.c b/components/dfs/src/dfs_file.c
index 32198371d7dd1e0fcaf925ac3d2df70d2c0ca61e..f5619e2354e6154023569b63b79f62ee99f951be 100644
--- a/components/dfs/src/dfs_file.c
+++ b/components/dfs/src/dfs_file.c
@@ -555,7 +555,7 @@ void ls(const char *pathname)
     if (pathname == RT_NULL) 
         rt_free(path);
 }
-FINSH_FUNCTION_EXPORT(ls, list directory contents)
+FINSH_FUNCTION_EXPORT(ls, list directory contents);
 
 void rm(const char *filename)
 {
@@ -564,7 +564,7 @@ void rm(const char *filename)
         rt_kprintf("Delete %s failed\n", filename);
     }
 }
-FINSH_FUNCTION_EXPORT(rm, remove files or directories)
+FINSH_FUNCTION_EXPORT(rm, remove files or directories);
 
 void cat(const char* filename)
 {
@@ -590,7 +590,7 @@ void cat(const char* filename)
 
     dfs_file_close(&fd);
 }
-FINSH_FUNCTION_EXPORT(cat, print file)
+FINSH_FUNCTION_EXPORT(cat, print file);
 
 #define BUF_SZ  4096
 static void copyfile(const char *src, const char *dst)
@@ -629,7 +629,15 @@ static void copyfile(const char *src, const char *dst)
         read_bytes = dfs_file_read(&src_fd, block_ptr, BUF_SZ);
         if (read_bytes > 0)
         {
-            dfs_file_write(&fd, block_ptr, read_bytes);
+			int length;
+			
+            length = dfs_file_write(&fd, block_ptr, read_bytes);
+			if (length != read_bytes)
+			{
+				/* write failed. */
+				rt_kprintf("Write file data failed, errno=%d\n", length);
+				break;
+			}
         }
     } while (read_bytes > 0);
 
diff --git a/components/dfs/src/dfs_posix.c b/components/dfs/src/dfs_posix.c
index 96139837e98ca5c871782dbef42884ac40e385c3..f516eccd93dde27ad341786f3dbebea6658a4269 100644
--- a/components/dfs/src/dfs_posix.c
+++ b/components/dfs/src/dfs_posix.c
@@ -33,11 +33,11 @@
 
 /**
  * this function is a POSIX compliant version, which will open a file and
- * return a file descriptor.
+ * return a file descriptor according specified flags.
  *
  * @param file the path name of file.
  * @param flags the file open flags.
- * @param mode
+ * @param mode ignored parameter
  *
  * @return the non-negative integer on successful open, others for failed.
  */
@@ -120,7 +120,8 @@ RTM_EXPORT(close);
  * @param buf the buffer to save the read data.
  * @param len the maximal length of data buffer
  *
- * @return the actual read data buffer length
+ * @return the actual read data buffer length. If the returned value is 0, it
+ * may be reach the end of file, please check errno.
  */
 int read(int fd, void *buf, size_t len)
 {
@@ -200,7 +201,7 @@ RTM_EXPORT(write);
  * @param offset the offset to be seeked.
  * @param whence the directory of seek.
  *
- * @return the current file position, or -1 on failed.
+ * @return the current read/write position in the file, or -1 on failed.
  */
 off_t lseek(int fd, off_t offset, int whence)
 {
@@ -336,6 +337,8 @@ RTM_EXPORT(stat);
  *
  * @param fildes the file description
  * @param buf the data buffer to save stat description.
+ *
+ * @return 0 on successful, -1 on failed.
  */
 int fstat(int fildes, struct stat *buf)
 {
@@ -470,7 +473,7 @@ RTM_EXPORT(rmdir);
  *
  * @param name the path name to be open.
  *
- * @return the DIR pointer of directory, NULL on open failed.
+ * @return the DIR pointer of directory, NULL on open directory failed.
  */
 DIR *opendir(const char *name)
 {