User-mode Linux kernel port

I have tried to re-compile linux-2.4.0-test4 and I could succeed only after
commenting out:
#include <unistd.h>
#include <fcntl.h>

from syscall_user.c and 
#include <unistd.h> from trap_user.c

Now when I launch the new kernel:
[root@... uml]# 2linux
tracing thread pid = 2330
Linux version 2.4.0-test4-1um (root@...) (gcc version 2.9
5.3 19991030 (prerelease)) #20 Tue Jul 18 19:23:17 PDT 2000
On node 0 totalpages: 4096
zone(0): 256 pages.
zone(1): 3840 pages.
zone(2): 0 pages.
Kernel command line: root=/dev/ubd0
Calibrating delay loop... 214.96 BogoMIPS
Memory: 16112k available
Dentry-cache hash table entries: 2048 (order: 2, 16384 bytes)
Buffer-cache hash table entries: 1024 (order: 0, 4096 bytes)
Page-cache hash table entries: 4096 (order: 2, 16384 bytes)
Inode-cache hash table entries: 1024 (order: 1, 8192 bytes)
POSIX conformance testing by UNIFIX
Linux NET4.0 for Linux 2.3
Based upon Swansea University Computer Society NET3.039
NET4: Unix domain sockets 1.0/SMP for Linux NET4.0.
NET4: Linux TCP/IP 1.0 for NET4.0
IP Protocols: ICMP, UDP, TCP
IP: routing cache hash table of 512 buckets, 4Kbytes
TCP: Hash tables configured (established 1024 bind 1024)
Starting kswapd v1.6
pty: 256 Unix98 ptys configured
RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize
loop: registered device at major 7
loop: enabling 8 loop devices
Initializing stdio console driver
Initializing software serial port version 0
serial line 0 assigned pty /dev/ptyp3
ssl receive thread is pid 2336
devfs: v0.102 (20000622) Richard Gooch (rgooch@...)
devfs: devfs_debug: 0x0
devfs: boot_options: 0x0
kmem_create: Forcing size word alignment - nfs_fh
VFS: Mounted root (ext2 filesystem) readonly.
Mounted devfs on /dev
INIT: version 2.77 booting
Activating swap...
Checking root file system...
Parallelizing fsck version 1.18 (11-Nov-1999)
fsck.ext2: No such file or directory while trying to open /dev/ubd/0
/dev/ubd/0: 
The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>


fsck failed.  Please repair manually and reboot.  Please note
that the root file system is currently mounted read-only.  To
remount it read-write:

   # mount -n -o remount,rw /

CONTROL-D will exit from this shell and REBOOT the system.

Give root password for maintenance
(or type Control-D for normal startup): 
***************************************

something goes wrong...and I see that no devices are created:

(none):~# ls /dev
console  initctl  loop  null  ptmx  pty     rd      tty   urandom
full     kmem     mem   port  pts   random  serial  ttys  zero
(none):~# 
***************************************

The root_fs I am using comes from the deb package. And when I boot the same
kernel version of the deb package everything is just fine. See below:
[....]
devfs: v0.102 (20000622) Richard Gooch (rgooch@...)
devfs: devfs_debug: 0x0
devfs: boot_options: 0x0
VFS: Mounted root (ext2 filesystem) readonly.
Mounted devfs on /dev
INIT: version 2.77 booting
Activating swap...
Checking root file system...
Parallelizing fsck version 1.18 (11-Nov-1999)
/dev/ubd/0 was not cleanly unmounted, check forced.
/dev/ubd/0: 4623/25688 files (0.6% non-contiguous), 44774/102400 blocks
Checking all file systems...
Parallelizing fsck version 1.18 (11-Nov-1999)
Mounting local file systems...
mount: devpts already mounted on /dev/pts
not mounting anything
Setting up IP spoofing protection: rp_filter.

Local time: Wed Jul 19 16:49:25 UTC 2000

Started device management daemon for /dev
Cleaning: /tmp /var/lock /var/run.
process 43 (rcS) segfaulted at address 0x0, ip = 0x809bd72
/etc/init.d/rcS: line 57:    43 Segmentation fault      ( trap - INT QUIT TSTP; set start; . $i )
Initializing random number generator... done.
Recovering nvi editor sessions... done.
INIT: Entering runlevel: 2
Starting system log daemon: syslogd  syslogd: /dev/xconsole: No such file or directory
 klogd.
Starting portmap daemon: portmap.
Starting internet superserver: inetd.

Debian GNU/Linux potato usermode ttys/0
[User Mode Kernel v0.14]
root password is "root"
guest password is "guest"
usermode login: 
*****************************

and ls /dev report everything ok.


Can somebody help me on this?

thanks in advance,
	Alessandro

p.s. Attached is my .config
#
# Automatically generated by make menuconfig: don't edit
#
CONFIG_NET=y
CONFIG_SYSVIPC=y
CONFIG_BSD_PROCESS_ACCT=y
CONFIG_BINFMT_ELF=y
CONFIG_BINFMT_MISC=y
CONFIG_BINFMT_AOUT=y
CONFIG_BLK_DEV_UBD=y
CONFIG_STDIO_CONSOLE=y
CONFIG_SSL=y
CONFIG_INET=y
CONFIG_1GB=y
CONFIG_UNIX98_PTYS=y
CONFIG_UNIX98_PTY_COUNT=256
CONFIG_NET_UMN=y
CONFIG_INET=y
CONFIG_UNIX=y
CONFIG_UID16=y
CONFIG_SYSCTL=y
CONFIG_BLK_DEV_RAM=y
CONFIG_MODULES=y
CONFIG_BLK_DEV_LOOP=y
CONFIG_IA64_PAGE_SIZE_16KB=y

#
# Processor features
#
# CONFIG_SMP is not set

#
# Filesystem support
#
CONFIG_PROMPT_FS=y

#
# File systems
#
# CONFIG_QUOTA is not set
CONFIG_AUTOFS_FS=y
CONFIG_AUTOFS4_FS=y
# CONFIG_ADFS_FS is not set
# CONFIG_ADFS_FS_RW is not set
# CONFIG_AFFS_FS is not set
# CONFIG_HFS_FS is not set
# CONFIG_BFS_FS is not set
# CONFIG_FAT_FS is not set
# CONFIG_MSDOS_FS is not set
# CONFIG_UMSDOS_FS is not set
# CONFIG_VFAT_FS is not set
# CONFIG_EFS_FS is not set
# CONFIG_JFFS_FS is not set
# CONFIG_CRAMFS is not set
# CONFIG_RAMFS is not set
# CONFIG_ISO9660_FS is not set
# CONFIG_JOLIET is not set
# CONFIG_MINIX_FS is not set
# CONFIG_NTFS_FS is not set
# CONFIG_NTFS_RW is not set
# CONFIG_HPFS_FS is not set
CONFIG_PROC_FS=y
CONFIG_DEVFS_FS=y
CONFIG_DEVFS_MOUNT=y
CONFIG_DEVFS_DEBUG=y
CONFIG_DEVPTS_FS=y
# CONFIG_QNX4FS_FS is not set
# CONFIG_QNX4FS_RW is not set
# CONFIG_ROMFS_FS is not set
CONFIG_EXT2_FS=y
# CONFIG_SYSV_FS is not set
# CONFIG_SYSV_FS_WRITE is not set
# CONFIG_UDF_FS is not set
# CONFIG_UDF_RW is not set
# CONFIG_UFS_FS is not set
# CONFIG_UFS_FS_WRITE is not set

#
# Network File Systems
#
# CONFIG_CODA_FS is not set
CONFIG_NFS_FS=y
# CONFIG_NFS_V3 is not set
# CONFIG_ROOT_NFS is not set
# CONFIG_NFSD is not set
# CONFIG_NFSD_V3 is not set
CONFIG_SUNRPC=y
CONFIG_LOCKD=y
# CONFIG_SMB_FS is not set
# CONFIG_NCP_FS is not set
# CONFIG_NCPFS_PACKET_SIGNING is not set
# CONFIG_NCPFS_IOCTL_LOCKING is not set
# CONFIG_NCPFS_STRONG is not set
# CONFIG_NCPFS_NFS_NS is not set
# CONFIG_NCPFS_OS2_NS is not set
# CONFIG_NCPFS_SMALLDOS is not set
# CONFIG_NCPFS_MOUNT_SUBDIR is not set
# CONFIG_NCPFS_NDS_DOMAINS is not set
# CONFIG_NCPFS_NLS is not set
# CONFIG_NCPFS_EXTRAS is not set

#
# Partition Types
#
# CONFIG_PARTITION_ADVANCED is not set
CONFIG_MSDOS_PARTITION=y
# CONFIG_NLS is not set

#
# Kernel hacking
#
CONFIG_DEBUGSYM=y