When a process opens a file, the POSIX-compliant open() library routine first sends the pathname to procnto, where the pathname is compared against the prefix tree to determine which resource managers should be sent the open() message.
The prefix tree may contain identical or partially overlapping regions of authority—multiple servers can register the same prefix. If the regions are identical, the order of resolution can be specified (see "Ordering mountpoints"). If the regions are overlapping, the responses from the path manager are ordered with the longest prefixes first; for prefixes of equal length, the same specified order of resolution applies as for identical regions.
For example, suppose we have these prefixes registered:
| Prefix | Description |
|---|---|
| / | QNX 4 disk-based filesystem (fs-qnx4.so) |
| /dev/ser1 | Serial device manager (devc-ser*) |
| /dev/ser2 | Serial device manager (devc-ser*) |
| /dev/hd0 | Raw disk volume (devb-eide) |
The filesystem manager has registered a prefix for a mounted QNX 4 filesystem (i.e., /). The block device driver has registered a prefix for a block special file that represents an entire physical hard drive (i.e., /dev/hd0). The serial device manager has registered two prefixes for the two PC serial ports.
The following table illustrates the longest-match rule for pathname resolution:
| This pathname: | matches: | and resolves to: |
|---|---|---|
| /dev/ser1 | /dev/ser1 | devc-ser* |
| /dev/ser2 | /dev/ser2 | devc-ser* |
| /dev/ser | / | fs-qnx4.so |
| /dev/hd0 | /dev/hd0 | devb-eide.so |
| /usr/jhsmith/test | / | fs-qnx4.so |