i'm sure i'm going to embarrass myself here but i was perusing the
char drivers for nice examples, and i ran across this excerpt in
pc8736x_gpio.c:
===== begin =====
if (major) {
devid = MKDEV(major, 0);
rc = register_chrdev_region(devid, PC8736X_GPIO_CT, DEVNAME);
} else {
rc = alloc_chrdev_region(&devid, 0, PC8736X_GPIO_CT, DEVNAME);
major = MAJOR(devid);
}
if (rc < 0) {
dev_err(&pdev->dev, "register-chrdev failed: %d\n", rc);
goto undo_request_region;
}
if (!major) {
major = rc;
dev_dbg(&pdev->dev, "got dynamic major %d\n", major);
}
===== end =====
i'm good with most of that -- if the (parameter) major is explicit,
then a dev_t of "devid" is created and register_chrdev_region() is
used.
on the other hand, if major is zero, then alloc_chrdev_region() is
used for *dynamic* allocation of the major number. in both cases, the
return code "rc" is saved and, if it's < 0, we have an error. and
that's where the confusion comes in.
i always thought both of those routines returned a simple zero to
indicate success. but look at those last few lines -- that return
code is assigned to "major", at which point it's *that* value that's
printed. wouldn't that just be zero all the time?
and wouldn't it also print that this was a "dynamic" major even if
the user specified an explicit major number at load time? this second
point is more nitpicky, but what about that first point? wouldn't a
successful registration always print an allocated major number of
zero?
rday
--
========================================================================
Robert P. J. Day Ottawa, Ontario, CANADA
http://crashcourse.ca
Twitter: http://twitter.com/rpjday
LinkedIn: http://ca.linkedin.com/in/rpjday
========================================================================
_______________________________________________
Kernelnewbies mailing list
Kernelnewbies@xxxxxxxxxxxxxxxxx
http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
