website: docs: zh_CN: Sync to en as path_umount (#1516)

Signed-off-by: xiaoleGun <1592501605@qq.com>

website/docs/zh_CN/guide/how-to-integrate-for-non-gki.md

@@ -291,6 +291,55 @@ index 45306f9ef247..815091ebfca4 100755
  		add_input_randomness(type, code, value);
 ```
 
+### 如何backport(向旧版本移植) path_umount {#how-to-backport-path-umount}
+
+你可以通过从K5.9向旧版本移植`path_umount`，在GKI之前的内核上获得卸载模块的功能。你可以通过以下补丁作为参考:
+
+```diff
+--- a/fs/namespace.c
++++ b/fs/namespace.c
+@@ -1739,6 +1739,39 @@ static inline bool may_mandlock(void)
+ }
+ #endif
+
++static int can_umount(const struct path *path, int flags)
++{
++	struct mount *mnt = real_mount(path->mnt);
++
++	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
++		return -EINVAL;
++	if (!may_mount())
++		return -EPERM;
++	if (path->dentry != path->mnt->mnt_root)
++		return -EINVAL;
++	if (!check_mnt(mnt))
++		return -EINVAL;
++	if (mnt->mnt.mnt_flags & MNT_LOCKED) /* Check optimistically */
++		return -EINVAL;
++	if (flags & MNT_FORCE && !capable(CAP_SYS_ADMIN))
++		return -EPERM;
++	return 0;
++}
++
++int path_umount(struct path *path, int flags)
++{
++	struct mount *mnt = real_mount(path->mnt);
++	int ret;
++
++	ret = can_umount(path, flags);
++	if (!ret)
++		ret = do_umount(mnt, flags);
++
++	/* we mustn't call path_put() as that would clear mnt_expiry_mark */
++	dput(path->dentry);
++	mntput_no_expire(mnt);
++	return ret;
++}
+ /*
+  * Now umount can handle mount points as well as block devices.
+  * This is important for filesystems which use unnamed block devices.
+```
+
 改完之后重新编译内核即可。
 
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