Drivers and the Kernel

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Roles of the Kernel – (1)

Components of a UNIX System

• User-level programs

• Kernel

• Hardware

Kernel manages the resources

• CPU – process management

• Memory – memory management

• I/O devices – device management

Kernel provides method for

• Inter-process communication (IPC)

Synchronization, communication

• Processes to request resources

System calls

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Roles of the Kernel – (2)

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Kernel-wide Design Approaches

Monolithic kernels

• Kernel space, shared memory, fast, …, need reboot

• Eg. Linux, *BSD, MS-DOS, MS Windows 9x series…

Microkernels

• User space, message passing, slow, …, as services

• Eg. Mac OS X, BeOS, …

Hybrid

• Monolithic + Micro

• Eg. MS Windows NT series, DragonFly BSD, …

Nanokernels

Exokernels

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Why Build a Custom Kernel

FreeBSD kernel

• Monolithic modular

• The functionality cannot be dynamically loadable

Building a custom kernel

• To be an advanced BSD user

• Time-consuming task

Customized kernel vs. GENERIC

• Fast boot time

• Lower memory usage

• Additional hardware support

• Fine-tune system performance

Such as adjusting important system parameters

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Finding the System Hardware

Before venturing into kernel configuration

• Get an inventory of the machine’s hardware

• Microsoft's Device Manager

dmesg

• cat /var/run/dmesg.boot

pciconf -lv

• man 4 ath

• man -k Atheros

psm0: <PS/2 Mouse> irq 12 on atkbdc0

psm0: [GIANT-LOCKED]

psm0: [ITHREAD] psm0: model Generic PS/2 mouse, device ID 0

ath0@pci0:3:0:0: class=0x020000 card=0x058a1014 chip=0x1014168c

vendor = 'Atheros Communications Inc.'

device = 'AR5212 Atheros AR5212 802.11abg wireless'

class = network subclass = ethernet

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Kernel Drivers and Modules

Before building a custom kernel

• Load kernel modules to get the specific hardware support

Kernel modules

• kldstat

• kldload

/boot/kernel/*.ko

Modify /boot/loader.conf to load modules in boot time automatically

– if_ath_load="YES"

• kldunload

zfs [/home/liuyh] -liuyh- kldstat Id Refs Address Size Name 1 62 0xffffffff80100000 6a2dc8 kernel 2 1 0xffffffff807a3000 1abd08 zfs.ko 3 2 0xffffffff8094f000 3a68 opensolaris.ko 4 4 0xffffffff80953000 1f348 krpc.ko 5 1 0xffffffff80973000 bc28 geom_label.ko

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Building and Installing a Custom Kernel – (1)

Obtain full FreeBSD source tree

• sysinstall

Configure Distributions src All

• csup

csup -h cvsup.tw.freebsd.org /usr/share/examples/cvsup/standard-supfile

Customized kernel configuration file

• Sample files

/usr/src/sys/<ARCH>/conf

– GENERIC, NOTES, LINT (generated by “make LINT”)

– /usr/src/sys/conf/NOTES for architecture independent options

• Customized file

cp GENERIC /usr/local/etc/MYKERNEL

ln -s /usr/local/etc/MYKERNEL /usr/src/sys/<ARCH>/conf/

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Building and Installing a Custom Kernel – (2)

Building a kernel

• cd /usr/src

• make buildkernel KERNCONF=MYKERNEL

• make installkernel KERNCONF=MYKERNEL

kernel = buildkernel + installkernel

• MODULES_OVERRIDE

Set to a list of modules to build instead of all of them

• NO_MODULES

Set to not build modules with the kernel

• WITHOUT_MODULES

Set to a list of modules to exclude from the build

Kernel locations

• /boot/kernel/kernel

• /boot/kernel /boot/kernel.old

make.conf(5)

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The Configuration File

Each line contains a keyword and one or more arguments • http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig-config.html

Keyword Function Example

machine Sets the machine type i386 or amd64

cpu Sets the CPU type I686_CPU or HAMMER

ident Sets the name of the kernel MYKERNEL

options Sets various comiple-time options INET or INET6

device Declares devices fxp

include Include another kernel config file GENERIC

nooptions Unset options MD_ROOT

nodevice Unset devices fdc

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If Something Goes Wrong

Config failed

• Make sure the keyword is typed correctly

Make failed

• Look over your configuration

• Send mail to the FreeBSD general questions mailing list with kernel configuration

Boot failed

• ok mode

boot kernel.old

unload kernel && load /boot/kernel.old/kernel && boot

• nextboot(8)

ps(1) failed

• Recompile and install a world

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Ok mode

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Tuning the FreeBSD Kernel

sysctl command

• Dynamically set or get kernel parameters

• All changes made by sysctl will be lost across reboot

• Use sysctl to tune the kernel and test it, then recompile the kernel

• Format:

% sysctl [options] name[=value] …

Ex:

% sysctl –a list all kernel variables

% sysctl –d kern.maxfiles print the description of the variable

% sysctl kern.maxfiles print the value of the variable

% sudo sysctl kern.maxfiles=2048

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Reference

References

• http://www.freebsd.org/doc/en/books/handbook/kernelconfig-

config.html

• /usr/src/sys/<ARCH>/conf

NOTES

LINT

GENERIC

Further reading

• http://www.freebsd.org/doc/handbook/configtuning-kernel-

limits.html

• http://www.freebsd.org/doc/en/books/developers-

handbook/kerneldebug.html