Linux kernel device driver Linux kernel module loading mechanism notes summary

#include <linux/moduleparam.h>

1. Module parameters

Defining variables in the driver

static int num = 0; //When the loading module does not specify the value of num, it is 0

module_param(variable name, type, permissions); type: byte, int, uint, short, ushort, long, ulong, bool, charp, permissions cannot have write permissions
Pass parameters: insmod test.ko variable name 1 = value 1 variable name 2 = value 2

The calling relationship of module_param is as follows:

#define module_param(name, type, perm) \
module_param_named(name, name, type, perm)
#define module_param_named(name, value, type, perm) \
param_check_##type(name, &(value)); \
module_param_call(name, param_set_##type, param_get_##type, &value, perm); \
__MODULE_PARM_TYPE(name, #type)
#define module_param_call(name, set, get, arg, perm) \
__module_param_call(MODULE_PARAM_PREFIX, \
  name, set, get, arg, \
  __same_type(*(arg), bool), perm)
#define __module_param_call(prefix, name, set, get, arg, isbool, perm) \
static int __param_perm_check_##name __attribute__((unused)) = \
BUILD_BUG_ON_ZERO((perm) < 0 || (perm) > 0777 || ((perm) & 2)) \
+ BUILD_BUG_ON_ZERO(sizeof(""prefix) > MAX_PARAM_PREFIX_LEN); \
static const char __param_str_##name[] = prefix #name; \
static struct kernel_param __moduleparam_const __param_##name \
__used \
  __attribute__ ((unused,__section__ ("__param"),aligned(sizeof(void *)))) \
= { __param_str_##name, perm, isbool ? KPARAM_ISBOOL : 0, \
  set, get, { arg } }

Multiple c files can be compiled into a module, which can be achieved using the instructions in the Makefile xxx-objs, as follows:

test-objs := ao bo //Compile into test.ko from ac and bc. Note that there cannot be a .o file with the same name as the target ko file obj-m += test.o

You can view the module information in the system under /sys/module/module name/

1. View the information of the elf file

readelf test.ko -a

Ko file composition

1. elf file header
2. text data ...
3. Sections table
4. Symbol table

2. EXPORT_SYMBOL(function name/variable address) //Export the address of the function/or variable to the kernel symbol table

EXPORT_SYMBOL_GPL(function name)
///////////

/proc/kallsyms View the symbol table of the current system

Summarize

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