1，VFS代码中不修改参数增加const修饰
2，fs_file_mapping.c: 增加安全函数的判空
3，path_cache.c: sizeof改为使用类型
4，fs_syscall.c: 对NULL解引用

close: I3UMWD
Signed-off-by: yansira <yansira@hotmail.com>

Change-Id: Ib99e937093336cfb16c44d0f811613d90f1b2f13

Change-Id: I832a8c1d4110b414214e88d09483ec4f5d7bf4a4

Change-Id: I19322f5dd90eb4a6642c97df8710958819eb9d98

fix:compatible with the old version of nfs server, add unmount ops.

Feature or Bugfix:Feature
Binary Source:Huawei
PrivateCode(Yes/No):Yes

Change-Id: I175d2648bc6f9078c34de2c0a5c93fda10b86c47
ChangeID:13306420