Unmounting a File System
The workshop manual for my MG usually describes assembly as the reverse of
disassembly and the reverse is more or less true for unmounting a file system.
A file system cannot be unmounted if something in the system is using one of its
So, for example, you cannot umount /mnt/cdrom if a process is using that
directory or any of its children.
If anything is using the file system to be unmounted there may be VFS inodes
from it in the VFS inode cache, and the code checks for this by looking through
the list of inodes looking for inodes owned by the device that this file system
If the VFS superblock for the mounted file system is dirty, that is it has
been modified, then it must be written back to the file system on disk.
Once it has been written to disk, the memory occupied by the VFS superblock
is returned to the kernel's free pool of memory.
Finally the vfsmount data structure for this mount is unlinked from
vfsmntlist and freed.