Getting Started with QNX Neutrino - QNX Software Systems

© 2009, QNX Software Systems GmbH & Co. KG. Writing a resource manager
The dev member contains the device number and is described below in “Of device
numbers, inodes, and our friend rdev.”
The blocksize describes the native blocksize of the device in bytes. For example, on a
typical rotating-medium storage system, this would be the value 512.
Finally, the funcs pointer points to a structure (from ):
typedef struct _iofunc_funcs {
unsigned nfuncs;
IOFUNC_OCB_T *(*ocb_calloc)
(resmgr_context_t *ctp,
IOFUNC_ATTR_T *attr);
void
(*ocb_free)
(IOFUNC_OCB_T *ocb);
} iofunc_funcs_t;
As with the connect and I/O functions tables, the nfuncs member should be stuffed
with the current size of the table. Use the constant _IOFUNC_NFUNCS for this.
The ocb_calloc and ocb_free function pointers can be filled with addresses of
functions to call whenever an OCB is to be allocated or deallocated. We’ll discuss why
you’d want to use these functions later when we talk about extending OCBs.
Of device numbers, inodes, and our friend rdev
The mount structure contains a member called dev. The attributes structure contains
two members: inode and rdev. Let’s look at their relationships by examining a
traditional disk-based filesystem. The filesystem is mounted on a block device (which
is the entire disk). This block device might be known as /dev/hd0 (the first hard disk
in the system). On this disk, there might be a number of partitions, such as
/dev/hd0t77 (the first QNX filesystem partition on that particular device). Finally,
within that partition, there might be an arbitrary number of files, one of which might
be /hd/spud.txt.
The dev (or “device number”) member, contains a number that’s unique to the node
that this resource manager is registered with. The rdev member is the dev number of
the root device. Finally, the inode is the file serial number.
(Note that you can obtain major and minor device numbers by calling
rsrcdbmgr_devno_attach(); see the Neutrino Library Reference for more details. You
are limited to 64 major devices and 1024 minor devices per major device.)
Let’s relate that to our disk example. The following table shows some example
numbers; after the table we’ll take a look at where these numbers came from and how
they’re related.
April 30, 2009 Chapter 5 • Resource Managers 225