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Kernel module - Check whether file (/dev node) exists

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Old 07-12-2012
Kernel module - Check whether file (/dev node) exists
Hi, I'm pretty new to kernel coding and I'm working on a device driver that works with an existing framework.

Basically my module will be loaded/unloaded multiple times and I'd like to create a register a class, driver, and create a /dev node on the first load only. The existing framework doesn't allow me to clean up much when my module is unloaded, so I'll just be reusing the earlier /dev node.

Is there a way in the Linux kernel to check whether this dev node already exists? I've seen filp_open but most people caution against opening files from kernel so is there an alternate way of checking? Is it possible/easier to check whether the driver or class exist?

Thanks a lot,
ThomasBrez
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LEARN ABOUT DEBIAN

multi_driver_module

DRIVER_MODULE(9)					   BSD Kernel Developer's Manual					  DRIVER_MODULE(9)

NAME

     DRIVER_MODULE -- kernel driver declaration macro

SYNOPSIS

     #include <sys/param.h>
     #include <sys/kernel.h>
     #include <sys/bus.h>
     #include <sys/module.h>

     DRIVER_MODULE(name, busname, driver_t driver, devclass_t devclass, modeventhand_t evh, void *arg);

     MULTI_DRIVER_MODULE(name, busname, driver_t drivers[], devclass_t devclass, modeventhand_t evh, void *arg);

DESCRIPTION

     The DRIVER_MODULE() macro declares a kernel driver.  DRIVER_MODULE() expands to the real driver declaration, where the phrase name is used as
     the naming prefix for the driver and its functions.  Note that it is supplied as plain text, and not a char or char *.

     busname is the parent bus of the driver (PCI, ISA, PPBUS and others), e.g. 'pci', 'isa', or 'ppbus'.

     The identifier used in DRIVER_MODULE() can be different from the driver name.  Also, the same driver identifier can exist on different
     busses, which is a pretty clean way of making front ends for different cards using the same driver on the same or different busses.  For
     example, the following is allowed:

     DRIVER_MODULE(foo, isa, foo_driver, foo_devclass, NULL, NULL);

     DRIVER_MODULE(foo, pci, foo_driver, foo_devclass, NULL, NULL);

     driver is the driver of type driver_t, which contains the information about the driver and is therefore one of the two most important parts
     of the call to DRIVER_MODULE().

     The devclass argument contains the kernel-internal information about the device, which will be used within the kernel driver module.

     The evh argument is the event handler which is called when the driver (or module) is loaded or unloaded (see module(9)).

     The arg is unused at this time and should be a NULL pointer.

     MULTI_DRIVER_MODULE() is a special version of DRIVER_MODULE(), which takes a list of drivers instead of a single driver instance.

SEE ALSO

     device(9), driver(9), module(9)

AUTHORS

     This manual page was written by Alexander Langer <alex@FreeBSD.org>.

BSD
								   May 16, 2000 							       BSD