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Operating Systems Linux Fedora Is Kernel module is the same as a device driver? Post 302519242 by Perderabo on Tuesday 3rd of May 2011 11:58:17 AM
Old 05-03-2011
On RedHat at least we have /usr/include/linux/major.h which documents which major number goes with which driver. And remember that there are character drivers and block drivers and one of each can use the same major number. By convention, when this happens the two drivers should be closely related. For example:
Code:
#define MEM_MAJOR               1
#define RAMDISK_MAJOR           1

is an excerpt from that header file and we have
Code:
     $ ls -l /dev | awk '$5 == "1,"' | sort -k1.1,1.1  -k6
brw-r----- 1 root  disk     1,     0 Jan 17 10:38 ram0
brw-r----- 1 root  disk     1,     1 Jan 17 10:38 ram1
brw-r----- 1 root  disk     1,     2 Jan 17 10:38 ram2
brw-r----- 1 root  disk     1,     3 Jan 17 10:38 ram3
brw-r----- 1 root  disk     1,     4 Jan 17 10:38 ram4
brw-r----- 1 root  disk     1,     5 Jan 17 10:38 ram5
brw-r----- 1 root  disk     1,     6 Jan 17 10:38 ram6
brw-r----- 1 root  disk     1,     7 Jan 17 10:38 ram7
brw-r----- 1 root  disk     1,     8 Jan 17 10:38 ram8
brw-r----- 1 root  disk     1,     9 Jan 17 10:38 ram9
brw-r----- 1 root  disk     1,    10 Jan 17 10:38 ram10
brw-r----- 1 root  disk     1,    11 Jan 17 10:38 ram11
brw-r----- 1 root  disk     1,    12 Jan 17 10:38 ram12
brw-r----- 1 root  disk     1,    13 Jan 17 10:38 ram13
brw-r----- 1 root  disk     1,    14 Jan 17 10:38 ram14
brw-r----- 1 root  disk     1,    15 Jan 17 10:38 ram15
crw-r----- 1 root  kmem     1,     1 Jan 17 15:38 mem
crw-rw-rw- 1 root  root     1,     3 Jan 17 15:38 null
crw-r----- 1 root  kmem     1,     4 Jan 17 15:38 port
crw-rw-rw- 1 root  root     1,     5 Jan 17 15:38 zero
crw-rw-rw- 1 root  root     1,     7 Jan 17 15:38 full
crw-rw-rw- 1 root  root     1,     8 Jan 17 15:38 random
cr--r--r-- 1 root  root     1,     9 Jan 17 15:38 urandom
crw------- 1 root  root     1,    11 Jan 17 15:38 kmsg
crw------- 1 root  root     1,    12 Jan 17 15:38 oldmem
$

The major number just tells the kernel which driver to invoke. The driver is the part of the kernel that understands its own minor numbers. But there are conventions here too.

Not all driver writers completely follow conventions. Smilie
 

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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
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