o 個人用のメモなので不明な点多いと思いますがごめんなさい

0. kernelを作る
   options         MEMORY_DISK_HOOKS
   options         MEMORY_DISK_IS_ROOT
   options         MINIROOTSIZE=大きさ(block)
   
1. crunch binaryをつくる
(/usr/src/distrib/i386/floppies/ramdisk/ 参照)
  - crunchgenのconfig fileを書く
    /bin, /sbin が必要なのでこのへんを progs に書く
    変な呼ばれかた(あるいは test と [ は同じとか)は ln に書く．
    shellは _cshとかいろいろ考えられるのでcrunchしないほうが無難かも．

  - crunchgen すると makefileができるので make

2. root filesystem の imageを作る
   - 適切な大きさの(MINIROOTSIZEを越えないように)ファイルを作る．
   - vnconfig して newfs．上で作ったファイルの大きさに適合したdiskを
     disktabに書いておくと楽
   - mountして / に必要なファイルを押し込む．
     MAKEDEVしわすれないように．
     とりあえずイメージをffs上に組んでtarでcopyしたりした．

3. rootfsのimageをkernelに組込む
   -  mdsetimage -v netbsd rootfs.img

でできあがりです．

付録: 

crunchgenの設定ファイル
---8<---
# ramdiskbin.conf - unified binary for the install ramdisk

srcdirs bin sbin sys/arch/i386/stand

progs cat chio chmod cp csh date dd df domainname echo ed expr hostname kill ksh ln ls mkdir mt mv pax pwd rcmd rcp rm rmdir sh sleep stty sync test

progs atactl badsect clri disklabel dump fsck fsck_ext2fs fsck_ffs fsck_lfs fsck_msdos fsdb fsirand ifconfig init ldconfig lmcctl mknod modload modunload mount mount_ados mount_cd9660 mount_ext2fs mount_fdesc mount_ffs mount_filecore mount_kernfs mount_lfs mount_msdos mount_nfs mount_null mount_procfs mount_umap mount_union newfs newfs_lfs newfs_msdos ping raidctl reboot restore rndctl route routed scsictl shutdown slattach swapctl ttyflags tunefs umount wsconsctl

# "special" gzip is actually larger assuming nothing else uses -lz..
#special gzip srcdir distrib/utils/x_gzip

ln pax tar
ln sh -sh
ln csh _csh
ln test [
ln mount_cd9660 cd9660
ln mount_ffs ffs
ln mount_msdos msdos
ln mount_nfs nfs
ln mount_kernfs kernfs
ln newfs mount_mfs
ln reboot halt
ln restore rrestore
ln swapctl swapon
ln mount_ffs mount_ufs 
ln dump rdump

# libhack.o is built by Makefile & included Makefile.inc
libs libhack.o -ledit -lutil -lcurses -ltermcap -lrmt -lcrypt -ll -lm

---8<---

disktabエントリ(6Mbyte):

md6m:\
	:ty=floppy:se#512:nt#1:rm#300:ns#12288:nc#1:\
	:pa#12288:oa#0:ba#4096:fa#512:ta=4.2BSD:\
	:pb#12288:ob#0:\
	:pc#12288:oc#0:

---8<---

2, 3 のための Makefile

IMAGE=		ramdisk.fs
MOUNT_POINT?=	/mnt
# DEV/RDEV file system device, CDEV/RDEV vnconfig device
VND?=		vnd0
VND_DEV=	/dev/${VND}a
VND_RDEV=	/dev/r${VND}a
VND_CDEV=	/dev/${VND}d
VND_CRDEV=	/dev/r${VND}d
MDEC=           ${DESTDIR}/usr/mdec
DISKTAB=	${.CURDIR}/disktab
DISKSIZE=	12288
DISKTYPE=	md6m
BASEROOT=	./mfsroot
KERN?=  /usr/src/sys/arch/i386/compile/VAI-O-LA+RAMDISK+V6/netbsd

all:

ramdisk: 
	dd if=/dev/zero of=${IMAGE} count=${DISKSIZE}
	vnconfig -v -c ${VND_CDEV} ${IMAGE} 512/${DISKSIZE}/1/1
	disklabel -f ${DISKTAB} -rw ${VND_CDEV} ${DISKTYPE}
	newfs -B le -m 0 -o space -i 5120 -c 1 ${VND_RDEV} ${DISKTYPE}
	${MDEC}/installboot -v -f ${MDEC}/biosboot.sym ${VND_RDEV}
	mount ${VND_DEV} ${MOUNT_POINT}
	(cd ${BASEROOT} ; tar cf - . ) | (cd ${MOUNT_POINT}; tar xvBpf -) 
	-mkdir ${MOUNT_POINT}/dev;
	cp -p /dev/MAKEDEV* ${MOUNT_POINT}/dev;
	(cd ${MOUNT_POINT}/dev; sh MAKEDEV all;)
	-mkdir -p ${MOUNT_POINT}/usr/mdec;
	cp -p /usr/mdec/biosboot.sym ${MOUNT_POINT}/usr/mdec
	cp -p /usr/mdec/mbr ${MOUNT_POINT}/usr/mdec
	cp -p /usr/mdec/mbr_bootsel ${MOUNT_POINT}/usr/mdec
	@echo ""
	@df -i ${MOUNT_POINT}
	@echo ""
	umount ${MOUNT_POINT}
	vnconfig -u ${VND_CDEV}

init:
	dd if=/dev/zero of=${IMAGE} count=${DISKSIZE}
	vnconfig -v -c ${VND_CDEV} ${IMAGE} 512/${DISKSIZE}/1/1
	disklabel -Rr ${VND_CDEV} ${DISKLABELFILE}
	newfs ${VND_RDEV}

config:
	vnconfig -v -c ${VND_CDEV} ${IMAGE} 512/${DISKSIZE}/1/1
	mount ${VND_DEV} ${MOUNT_POINT}

unconfig:
	-umount -f ${MOUNT_POINT}
	-vnconfig -u ${VND_DEV}

netbsd: ${KERN} ${IMAGE}
	cp ${KERN} netbsd
	mdsetimage -v netbsd ${IMAGE}
#	strip netbsd
#	gzip netbsd

clean:
	-rm *~ netbsd netbsd.gz ${IMAGE}