Linux kernel structure

1. Linux kernel structure Kernel code structure How it boots itself All the system calls are available System is configured Process handling is available ICOM 5007 - Noack

2. The kernel code • Obtaining it • Information 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 contains • The 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 ICOM 5007 - Noack

3. structure • Major directories • Arch – 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 ICOM 5007 - Noack

4. More structure • The auxiliary files • Makefile and rules • These explain quite a bit about kernel structure • Note – this makefile activates the others in each subdirectory • README • How to compile • Others • Casual reading – how Linux gets developed ICOM 5007 - Noack

5. Linux is ported to these architectures ICOM 5007 - Noack

6. View of the i386 arch area ICOM 5007 - Noack

7. Contents of lib for the i386 • Comments • The .S are assembly language – GNU, not Microsoft • Note the individual makefile • General utilities, as you would expect ICOM 5007 - Noack

8. The makefile for lib • Notes • The 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-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.o obj-$(CONFIG_DEBUG_IOVIRT) += iodebug.o include $(TOPDIR)/Rules.make ICOM 5007 - Noack

9. A sample of GNU assembler /* unsigned int csum_partial(const unsigned char * buff, int len, unsigned int sum) */ .text .align 4 .globl csum_partial pushl %esi pushl %ebx movl 20(%esp),%eax # Function arg: unsigned int sum movl 16(%esp),%ecx # Function arg: int len movl 12(%esp),%esi # Function arg: unsigned char *buff testl $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 ICOM 5007 - Noack

10. Some recognizable parts of kernel • Notes • This 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 ICOM 5007 - Noack

11. Tiny piece of kernel code from mm #if CONFIG_HIGHMEM pte_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 */ ICOM 5007 - Noack

12. The contents of fsThis shows all the file systemssupported by Linux ICOM 5007 - Noack

13. The non-architecture-dependentroutines of the kernel ICOM 5007 - Noack

14. The driver repertoire in general ICOM 5007 - Noack

15. The block device driversnote: paride contains the IDE drivers ICOM 5007 - Noack

16. A few of the char drivers ICOM 5007 - Noack

17. Comments - drivers • Block device drivers • All the common block devices – these include disks and anything else that is block-oriented • Character device drivers • These include the character-by-character devices – also some pseudo-devices • Note – these are architecture-independent ICOM 5007 - Noack

18. Some things that aren’t in the kernel • Anything that isn’t in vmlinuz • Examples: • 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 different • The 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 ICOM 5007 - Noack

19. 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 easier • The 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 ICOM 5007 - Noack