Getting Started with QNX Neutrino - QNX Software Systems

Writing a resource manager
© 2009, QNX Software Systems GmbH & Co. KG.
resmgr_attach()
resmgr_detach()
pulse_attach()
pulse_detach()
Creates a channel, associates a pathname, dispatch handle,
connect functions, I/O functions, and other parameters together.
Sends a message to the process manager to register the
pathname.
Opposite of resmgr_attach(); dissociates the binding of the
pathname and the resource manager.
Associates a pulse code with a function. Since the library
implements the message receive loop, this is a convenient way
of “gaining control” for handling pulses.
Dissociates a pulse code from the function.
In addition to the functions listed above, there are also numerous functions dealing
with the dispatch interface.
One function from the above list that deserves special mention is resmgr_open_bind().
It associates some form of context data when the connect message (typically as a
result of the client calling open() or fopen()) arrives, so that this data block is around
when the I/O messages are being handled. Why didn’t we see this in the /dev/null
handler? Because the POSIX-layer default functions call this function for us. If we’re
handling all the messages ourselves, we’d certainly call this function.
The resmgr_open_bind() function not only sets up the context block for further I/O
messages, but also initializes other data structures used by the resource manager
library itself.
The rest of the functions from the above list are somewhat intuitive — we’ll defer their
discussion until we use them.
The POSIX layer
The second layer provided by QSS’s resource manager library is the POSIX layer. As
with the base layer, you could code a resource manager without using it, but it would
be a lot of work! Before we can talk about the POSIX-layer functions in detail, we
need to look at some of the base layer data structures, the messages that arrive from
the clients, and the overall structure and responsibilities of a resource manager.
Writing a resource manager
Now that we’ve introduced the basics — how the client looks at the world, how the
resource manager looks at the world, and an overview of the two cooperating layers in
the library, it’s time to focus on the details.
In this section, we’ll take a look at the following topics:
• data structures
• resource manager structure
204 Chapter 5 • Resource Managers April 30, 2009