vfs_umount Entry Point

Purpose

Unmounts a virtual file system.

Syntax

int vfs_umount ( vfsp, crp) struct vfs *vfsp; struct ucred *crp;

Parameters

Item	Description
vfsp	Points to the vfs structure being unmounted. This structure is defined in the /usr/include/sys/vfs.h file.
crp	Points to the cred structure. This structure contains data that the file system can use to validate access permission.

Description

The vfs_umount entry point is called to unmount a virtual file system. The logical file system performs services independent of the virtual file system that initiate the unmounting. The logical file system services:

Guarantee the syntax of the uvmount subroutine.
Perform permission checks:
- If the vfsp parameter refers to a device mount, then the user must have root user authority to perform the operation.
- If the vfsp parameter does not refer to a device mount, then the user must have root user authority or write permission in the parent directory of the mounted-over virtual node (v-node), as well as write permission to the file represented by the mounted-over v-node.
Ensure that the virtual file system being unmounted contains no mount points for other virtual file systems.
Ensure that the root v-node is not in use except for the mount. The root v-node is also referred to as the mounted v-node.
Clear the v_mvfsp field in the stub v-node. This prevents lookup operations already in progress from traversing the soon-to-be unmounted mount point.

The logical file system assumes that, if necessary, successful vfs_umount entry point calls free the root v-node. An error return from the vfs_umount entry point causes the mount point to be re-established. A 0 (zero) returned from the vfs_umount entry point indicates the routine was successful and that the vfs structure was released.

Execution Environment

The vfs_umount entry point can be called from the process environment only.

Return Values

Item	Description
0	Indicates success.

Nonzero return values are returned from the /usr/include/sys/errno.h file to indicate failure.