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Linux kernel structure

Kernel code structureHow it boots itself

All the system calls are availableSystem is configured

Process handling is available

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The kernel code

Obtaining itInformation at www.kernel.org

ftp ftp.pr.kernel.org

Usually it is in/usr/src – various directories

Most recent stable version is 2.4.19

What it containsThe source code that compiles and links into a bootable system

The compressed version is vmlinuz

It contains all the openly available device drivers

Future drivers appear in future versions or can be compiled in the current version

Makefiles for automated configuration

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structure

Major directoriesArch – architecture-dependent

Documentation – read these

Drivers – all except network

Fs – the file system

Include – includes of multiple use

Init – from boot to running kernel

Ipc – IPC

Kernel – the kernel structures

Lib – libraries for the kernel

Mm – memory management

Net – the network code

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More structure

The auxiliary filesMakefile and rules

These explain quite a bit about kernel structure

Note – this makefile activates the others in each subdirectory

READMEHow to compile

OthersCasual reading –

how Linux gets developed

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Linux is ported to these architectures

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View of the i386 arch area

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Contents of lib for the i386

CommentsThe .S are assembly language – GNU, not Microsoft

Note the individual makefile

General utilities, as you would expect

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The makefile for lib

NotesThe CONFIG shell variables come from the make config step

Rules.make is used

The .S.o: rule does assembly instead of compilation because of the $(AFLAGS) argument

## Makefile for i386-specific library files..

# 

.S.o:$(CC) $(AFLAGS) -c $< -o $*.o

 L_TARGET = lib.a

 obj-y = checksum.o old-checksum.o delay.o \

usercopy.o getuser.o \memcpy.o strstr.o

 obj-$(CONFIG_X86_USE_3DNOW) += mmx.o

obj-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.oobj-$(CONFIG_DEBUG_IOVIRT) += iodebug.o

 include $(TOPDIR)/Rules.make

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A sample of GNU assembler

/*unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum) */

.text

.align 4

.globl csum_partialpushl %esipushl %ebxmovl 20(%esp),%eax # Function arg: unsigned int summovl 16(%esp),%ecx # Function arg: int lenmovl 12(%esp),%esi # Function arg: unsigned char *bufftestl $2, %esi # Check alignment.jz 2f # Jump if alignment is ok.subl $2, %ecx # Alignment uses up two bytes.jae 1f # Jump if we had at least two bytes.addl $2, %ecx # ecx was < 2. Deal with it.jmp 4f

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Some recognizable parts of kernel

NotesThis is the i386-

specific part of kernel

Note semaphore.c smp.c signal.c

Some of these files will show up in the arch-independent part also

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Tiny piece of kernel code from mm

#if CONFIG_HIGHMEMpte_t *kmap_pte;pgprot_t kmap_prot; #define kmap_get_fixmap_pte(vaddr) \

pte_offset(pmd_offset(pgd_offset_k(vaddr), (vaddr)), (vaddr)) void __init kmap_init(void){

unsigned long kmap_vstart; 

/* cache the first kmap pte */kmap_vstart = __fix_to_virt(FIX_KMAP_BEGIN);kmap_pte = kmap_get_fixmap_pte(kmap_vstart);

 kmap_prot = PAGE_KERNEL;

}#endif /* CONFIG_HIGHMEM */

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The contents of fsThis shows all the file systems supported by

Linux

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The non-architecture-dependentroutines of the kernel

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The driver repertoire in general

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The block device driversnote: paride contains the IDE drivers

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A few of the char drivers

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Comments - drivers

Block device driversAll the common block devices – these include disks and anything else

that is block-oriented

Character device driversThese include the character-by-character devices – also some

pseudo-devices

Note – these are architecture-independent

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Some things that aren’t in the kernel

Anything that isn’t in vmlinuzExamples:

Init – it reads /etc/inittab and starts all those processes

Startup scripts – these are called up by init using inittab

Libraries and most network daemons

The kernel and the distribution are differentThe distribution contains utilities and libraries for users

It contains the system installation utilities

Typical distributions are RedHat, Slackware, Suse

X-windows is part of the distribution or separately downloadable

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Some techniques for viewing the kernel

This is W2K and WXP – Obviously the kernel won’t compile here, but it makes nice slides

Open with permits viewing makefiles, etc.

Documentation directory contains .txt files Set the .txt association to word, not notepad

Viewing in Linux is a little easierThe usual gui lets you view the filesystem treewise

Clicking on individual .c, .h, .s, etc immediately displays the file in editor (emacs)

Learn to use grep and fgrep to find out where structures, etc. are defined

Learn to use du (disk usage) to get an idea of the size of the kernel