Communication via native IPC

Once a resource manager has established its pathname prefix, it will receive messages whenever any client program tries to do an open(), read(), write(), etc. on that pathname. For example, after devc-ser* has taken over the pathname /dev/ser1, and a client program executes:

fd = open ("/dev/ser1", O_RDONLY);

the client's C library will construct an _IO_CONNECT message, which it then sends to the devc-ser* resource manager via IPC.

Some time later, when the client program executes:

read (fd, buf, BUFSIZ);

the client's C library constructs an _IO_READ message, which is then sent to the resource manager.

A key point is that all communications between the client program and the resource manager are done through native IPC messaging. This allows for a number of unique features:

Note: All QNX Neutrino RTOS device drivers and filesystems are implemented as resource managers. This means that everything that a "native" QNX Neutrino device driver or filesystem can do, a user-written resource manager can do as well.

Consider FTP filesystems, for instance. Here a resource manager would take over a portion of the pathname space (e.g., /ftp) and allow users to cd into FTP sites to get files. For example, cd /ftp/ would connect to the FTP site and change directory to /pub. After that point, the user could open, edit, or copy files.

Application-specific filesystems would be another example of a user-written resource manager. Given an application that makes extensive use of disk-based files, a custom tailored filesystem can be written that works with that application and delivers superior performance.

The possibilities for custom resource managers are limited only by the application developer's imagination.