制作RAMDISK in KERNEL的NetBSD微系统
【FreeBSD教程】在前面我们已经讲过如何制作软盘上运行的FreeBSD和OpenBSD系统，现在我们来看看如何制作一个运行在软盘上的NetBSD系统。同软盘中的OpenBSD系统一样，我们还是将系统中的所有配制文件及程序全部存放到NetBSD的内核中，这样整个系统看起来就是一个文件。下面让我们具体来看看如何完成这样一个微系统的制作。
0、NetBSD的启动过程
当硬盘MBR中的引导程序接过启动之后，MBR中的程序将读入硬盘NetBSD分区中的引导程序，引导程序默认情况下会加载/boot，然后由boot载入内核/netbsd，此时内核开始检测一些硬件和做一些初始化。初始化完成后kernel将mount root device，然后启动系统初始化进程/sbin/init，init将根据/etc/rc中的设置来进行初始化等。
1、定制RAMDISK内核
要使用RAMDISK in KERNEL就必须在内核配制文件中加入以下选项： options MEMORY_DISK_HOOKS
options MEMORY_DISK_IS_ROOT # force root on memory disk
options MEMORY_DISK_SERVER=0
options MEMORY_DISK_ROOT_SIZE=10000 # size of memory disk, in blocks
options MEMORY_RBFLAGS=0x00 # boot in to multi-user mode
pseudo-device md 1 # memory disk device (ramdisk)
以上的内核参数意义如下：
MEMORY_DISK_ROOT_SIZE : 内存磁盘大小，以块为单位
MEMORY_RBFLAGS=0x00 : 启动到多用户模式
以下是在我机器上使用的一个内核配制文件
include "arch/i386/conf/std.i386"
#options INCLUDE_CONFIG_FILE # embed config file in kernel binary
makeoptions COPTS="-Os" # Optimise for space. Implies -O2
# Enable the hooks used for initializing the root memory-disk.
options MEMORY_DISK_HOOKS
options MEMORY_DISK_IS_ROOT # force root on memory disk
options MEMORY_DISK_SERVER=1 # 0 readonly 1 writable
options MEMORY_DISK_ROOT_SIZE=10000 # size of memory disk, in blocks
options MEMORY_RBFLAGS=0x00 # boot in to multi-user mode
maxusers 48 # estimated number of users
# CPU support. At least one is REQUIRED.
options I386_CPU
options I686_CPU
# CPU-related options.
options MATH_EMULATE # floating point emulation
# This option allows you to force a serial console at the specified
# I/O address.
#options CONSDEVNAME="/"com/"",CONADDR=0x3f8,CONSPEED=9600
# Avoid irq 5 and 7, the most likely cause of problems on modern laptops.
options PCIC_ISA_INTR_ALLOC_MASK=0xff5f
# Standard system options
options INSECURE # disable kernel security levels
options RTC_OFFSET=0 # hardware clock is this many mins. west of GMT
#options NTP # NTP phase/frequency locked loop
options USERCONF # userconf(4) support
options PIPE_SOCKETPAIR # smaller, but slower pipe(2)
options MALLOC_NOINLINE # Not inlining MALLOC saves memory
# File systems
file-system FFS # UFS
file-system MFS # memory file system
file-system MSDOSFS # MS-DOS file system
file-system KERNFS # /kern
options VNODE_OP_NOINLINE # Not inlining vnode op calls saves mem
# Networking options
options GATEWAY # packet forwarding
options INET # IP ICMP TCP UDP
#options PFIL_HOOKS # pfil(9) packet filter hooks
# builtin terminal emulations
options WSEMUL_VT100 # VT100 / VT220 emulation
# different kernel output - see dev/wscons/wsdisplayvar.h
options WS_KERNEL_FG=WSCOL_BLACK
options WS_KERNEL_BG=WSCOL_WHITE
# compatibility to other console drivers
#options WSDISPLAY_COMPAT_PCVT # emulate some ioctls
#options WSDISPLAY_COMPAT_SYSCONS # emulate some ioctls
#options WSDISPLAY_COMPAT_USL # VT handling
#options WSDISPLAY_COMPAT_RAWKBD # can get raw scancodes
# see dev/pckbc/wskbdmap_mfii.c for implemented layouts
#options PCKBD_LAYOUT="(KB_DE | KB_NODEAD)"
# allocate a number of virtual screens at autoconfiguration time
#options WSDISPLAY_DEFAULTSCREENS=4
# use a large software cursor that doesn't blink
options PCDISPLAY_SOFTCURSOR
# modify the screen type of the console; defaults to "80x25"
#options VGA_CONSOLE_SCREENTYPE="/"80x24/""
# Kernel root file system and dump configuration.
config netbsd root on ? type ?
#config netbsd root on sd0a type ffs
#config netbsd root on ? type nfs
#
# Device configuration
#
mainbus0 at root
cpu* at mainbus?
apm0 at mainbus0 # Advanced power management
# Basic Bus Support
# PCI bus support
pci* at mainbus? bus ?
pci* at pchb? bus ?
pci* at ppb? bus ?
# PCI bridges
pchb* at pci? dev ? function ? # PCI-Host bridges
pceb* at pci? dev ? function ? # PCI-EISA bridges
pcib* at pci? dev ? function ? # PCI-ISA bridges
ppb* at pci? dev ? function ? # PCI-PCI bridges
# XXX 'puc's aren't really bridges, but there's no better place for them here
puc* at pci? dev ? function ? # PCI "universal" comm. cards
# ISA bus support
isa0 at mainbus?
isa0 at pceb?
isa0 at pcib?
# ISA Plug-and-Play bus support
isapnp0 at isa?
# Coprocessor Support
# Math Coprocessor support
npx0 at isa? port 0xf0 irq 13 # x86 math coprocessor
# Console Devices
# ISA console
#pc0 at isa? port 0x60 irq 1 # pccons generic PC console driver
# wscons
pckbc0 at isa? # pc keyboard controller
pckbd* at pckbc? # PC keyboard
#pms* at pckbc? # PS/2 mouse for wsmouse
vga0 at isa?
vga* at pci? dev ? function ?
pcdisplay0 at isa? # CGA, MDA, EGA, HGA
wsdisplay* at vga? console ?
wsdisplay* at pcdisplay? console ?
wskbd* at pckbd? console ?
#wsmouse* at pms? mux 0
pcppi0 at isa?
sysbeep0 at pcppi?
# Serial Devices
# PCI serial interfaces
com* at puc? port ? # 16x50s on "universal" comm boards
#cy* at pci? dev ? function ? # Cyclades Cyclom-Y serial boards
# ISA Plug-and-Play serial interfaces
com* at isapnp? # Modems and serial boards
# ISA serial interfaces
#options COM_HAYESP # adds Hayes ESP serial board support
com0 at isa? port 0x3f8 irq 4 # Standard PC serial ports
com1 at isa? port 0x2f8 irq 3
com2 at isa? port 0x3e8 irq 5
#com3 at isa? port 0x2e8 irq 9
#ast0 at isa? port 0x1a0 irq 5 # AST 4-port serial cards
#com* at ast? slave ?
#boca0 at isa? port 0x100 irq 5 # BOCA 8-port serial cards
#com* at boca? slave ?
#tcom0 at isa? port 0x100 irq 7 # TC-800 8-port serial cards
#com* at tcom? slave ?
#rtfps0 at isa? port 0x1230 irq 10 # RT 4-port serial cards
#com* at rtfps? slave ?
#cy0 at isa? iomem 0xd4000 irq 12 # Cyclades serial cards
# Miscellaneous mass storage devices
# Network Interfaces
# PCI network interfaces
fxp* at pci? dev ? function ? # Intel EtherExpress PRO 10 /100B
le* at pci? dev ? function ? # PCnet-PCI Ethernet
pcn* at pci? dev ? function ? # AMD PCnet-PCI Ethernet
rtk* at pci? dev ? function ? # Realtek 8129/8139
amhphy* at mii? phy ? # AMD 79c901 Ethernet PHYs
urlphy* at mii? phy ? # Realtek RTL8150L internal PHYs
ukphy* at mii? phy ? # generic unknown PHYs
# Pseudo-Devices
# disk/mass storage pseudo-devices
pseudo-device md 1 # memory disk device (ramdisk)
#pseudo-device vnd 4 # disk-like interface to files
# network pseudo-devices
pseudo-device bpfilter 8 # Berkeley packet filter
pseudo-device ipfilter # IP filter (firewall) and NAT
pseudo-device loop # network loopback
pseudo-device ppp 2 # Point-to-Point Protocol
pseudo-device pppoe 3
# miscellaneous pseudo-devices
pseudo-device pty 2 # pseudo-terminals (Sysinst needs two)
# wscons pseudo-devices
pseudo-device wsmux # mouse & keyboard multiplexor
#pseudo-device wsfont
2、制作ramdisk镜像
# dd if=/dev/zero of=/ramdisk bs=512 count=9000
# vnconfig -c /dev/vnd0d /ramdisk
# disklabel -r -w /dev/vnd0d rdroot
# newfs -m 0 -S 512 -i 4096 /dev/vnd0a
# mount /dev/vnd0a /mnt
# mkdir /mnt/{dev,bin,sbin,etc}
# cp /dev/MAKEDEV /mnt/dev
# cp /bin/{sh,ls} /mnt/bin
# cp /sbin/init /mnt/sbin
# cd /mnt/dev/ && ./MAKEDEV ramdisk
# echo 'echo "This is my minibsd all in kernel" && /bin/sh' > /mnt/etc/rc
# sync && umount /mnt
# sync && vnconfig -u vnd0d && sync
3、将ramdisk写入kernel
# mdsetroot /minibsd ramdisk
4、压缩kernel大小
# gzip -9 -c /minibsd > /minibsd.gz
5、制作目标软盘
因为系统需要使用/boot（/usr/mdec/boot）来加载kernel，所以我们需要在软盘上放置boot文件。
# disklabel -B -w -r /dev/fd0a fd1440
# newfs -m 0 -S 512 /dev/fd0a
# mount /dev/fd0a /mnt
# cp /usr/mdec/boot /mnt
# cp /minibsd.gz /mnt/netbsd
现在你的ramdisk in kernel的mininetbsd系统就已经做好了。