This section summarizes the kernel functions, variables, macros,
and /proc files that we’ve touched on in this chapter. It is
meant to act as a reference. Each item is listed after the relevant
header file, if any. A similar section appears at the end of every chapter
from here on, summarizing the new symbols introduced in the chapter.
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__KERNEL__,MODULE Preprocessor symbols, which must both be defined to compile modularized kernel code.
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int init_module(void);,void cleanup_module(void); Module entry points, which must be defined in the module object file.
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#include <linux/module.h> -
MOD_INC_USE_COUNT;,MOD_DEC_USE_COUNT;,MOD_IN_USE Macros that act on the usage count.
- /proc/modules
The list of currently loaded modules. Entries contain the module name, the amount of memory they occupy, and the usage count. Extra strings are appended to each line to specify flags that are currently active for the module.
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int register_symtab(struct symbol_table *); Function used to specify the set of public symbols in the module. This function doesn’t exist any more in Linux 2.1.18 and newer kernels. See Section 17.1 in Chapter 17 for details.
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int register_symtab_from(struct symbol_table *, long *); Version 2.0 exports this function instead of register_symtab, which is a preprocessor macro instead. You’ll see register_symtab_from in
/proc/ksyms, but the source code doesn’t need to cope with it.-
#include <linux/symtab_begin.h>,X(symbol),,#include <linux/symtab_end.h> Headers and preprocessor macro used to declare a symbol table with 1.2 and 2.0 kernels. The interface to symbol tables changed in 2.1.1.
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#include <linux/version.h> Required header. It is included by
<linux/module.h>, unless__NO_VERSION__is defined (see below).-
LINUX_VERSION_CODE Integer macro, useful to
#ifdefversion dependencies.-
char kernel_version[] = UTS_RELEASE; Required variable in every module.
<linux/module.h>defines it, unless__NO_VERSION__is defined (see below).-
__NO_VERSION__ Preprocessor symbol. Prevents declaration of
kernel_versionin<linux/module.h>.-
#include <linux/sched.h> One of the most important header files. It’s unlikely you could do without it.
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struct task_struct *current; The current process.
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struct task_struct *current_set[]; Linux 2.0 supports symmetric multiprocessor boards and defines
currentas a macro that expands tocurrent_set[this_cpu]. You’ll seecurrent_setin/proc/ksyms, but code in the module still usescurrent. 2.1 development kernels introduced faster ways to accesscurrentwithout exporting a kernel symbol. See Section 17.11 in Chapter 17.-
current->pid,current->comm The process ID and command name for the current process.
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#include <linux/kernel.h>,int printk(const char * fmt, ...); The analogue of printf for kernel code.
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#include <linux/malloc.h>,void *kmalloc(unsigned int size, int priority);,void kfree(void *obj); Analogue of malloc and free for kernel code. Use the value of
GFP_KERNELas the priority.-
#include <linux/ioport.h>,int check_region(unsigned int from, unsigned int extent);,void request_region(unsigned int from, unsigned int extent,,const char *name);,void release_region(unsigned int from, unsigned int extent); Functions used to register and release I/O ports. Version 2.1.30 changed the
unsigned intarguments tounsigned long, but this change doesn’t affect driver code.-
#include <asm/system.h> This header defines macros like save_flags and restore_flags that access specific machine registers.
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save_flags(long flags);,restore_flags(long flags); Preprocessor macros meant to allow temporary modification of one processor flag.
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cli();,sti(); Disable and enable interrupts. sti shouldn’t be used; use save_flags and restore_flags instead.
- /proc/ksyms
The public kernel symbol table.
- /proc/ioports
The list of ports used by installed devices.