NFS 挂载出错，提示Root-NFS: No NFS server available, giving up.

求助啊，我虚拟机和开发板可以ping通，在虚拟机的/mnt也能成功挂载，使用光盘自带的文件系统root_qtopia_2.2.0_2.6.30.4_20100601.tar。大家帮忙解决一下，感激不尽···
提示的信息：
TCP cubic registered
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
lib80211: common routines for IEEE802.11 drivers
s3c2410-rtc s3c2410-rtc: setting system clock to 2008-11-10 13:15:15 UTC (1226322915)
Root-NFS: No NFS server available, giving up.
VFS: Unable to mount root fs via NFS, trying floppy.
VFS: Cannot open root device "nfs" or unknown-block(2,0)
Please append a correct "root=" boot option; here are the available partitions:
1f00             256 mtdblock0 (driver?)
1f01            3072 mtdblock1 (driver?)
1f02          257024 mtdblock2 (driver?)
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
Backtrace:
[<c0049048>] (dump_backtrace+0x0/0x10c) from [<c034f25c>] (dump_stack+0x18/0x1c)
r7:c380c0cb r6:c04bdd40 r5:c380c000 r4:c381df40
[<c034f244>] (dump_stack+0x0/0x1c) from [<c034f2ac>] (panic+0x4c/0x12c)
[<c034f260>] (panic+0x0/0x12c) from [<c0008e4c>] (mount_block_root+0x178/0x234)
r3:00000000 r2:c38313ec r1:c381df40 r0:c0417828
[<c0008cd4>] (mount_block_root+0x0/0x234) from [<c0008fb8>] (mount_root+0xb0/0xf4)
[<c0008f08>] (mount_root+0x0/0xf4) from [<c00090f4>] (prepare_namespace+0xf8/0x190)
r7:c04bd724 r6:c002083c r5:c002083c r4:c002084c
[<c0008ffc>] (prepare_namespace+0x0/0x190) from [<c0008478>] (kernel_init+0xc8/0xf4)
r7:00000000 r6:c001f2ac r5:c001ee90 r4:c001f2ac
[<c00083b0>] (kernel_init+0x0/0xf4) from [<c005a2cc>] (do_exit+0x0/0x620)
r7:00000000 r6:00000000 r5:00000000 r4:00000000

是挂载文件系统出的问题吧？
可能是nfs没有开启，开启命令：/etc/init.d/nfs start