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, dinit, and chkfsys) that need to move between the filesystem and the host/image of that filesystem.

For example, consider a disk with /dev/hd0t79 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:

Command /dev/hd0t79 / /tmp
ON /dev/hd0 /dev/hd0t79 /dev/hd0t79
AT /dev/hd0t79 / /
BY /    

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