Mounting options

The DCMD_FSYS_MOUNTED_ON, DCMD_FSYS_MOUNTED_AT, and DCMD_FSYS_MOUNTED_BY commands allow traversal of the filesystem hierarchy by utilities (like df) that need to move between the filesystem and the host/image of that filesystem.

For example, consider a disk with /dev/hd0t179 as a partition of /dev/hd0, mounted at the root (/), with a directory /tmp. The table below gives a summary of the responses for each command (shortened to just the two last letters of the command) for each entity:

ENODEV is returned when there is no such entity (for example, an ON query of /dev/hd0, or a BY query of /).

Basically:

• ON means “Who am I on top of?”
• BY means “Who is on top of me?”
• AT means “Where am I? Who is my owner?”