iostat with -x option isn't working for me.  I am using a 2.4.4-ac9 kernel
I built myself, so I don't know if there's some kernel patch missing that
you have in your kernel ...

Basically it's just printing the header line, but then no device stats,
with this option; whether or not I provide a device name:

[root@localhost kernel]# uname -a
Linux localhost.localdomain 2.4.4-ac9 #1 Wed May 16 21:39:29 BST 2001 i586
unknown
[root@localhost kernel]# iostat -x
Linux 2.4.4-ac9 (localhost.localdomain)         07/07/01

avg-cpu:  %user   %nice    %sys   %idle
           8.50    0.12    1.24   90.14
Device:  rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s avgrq-sz avgqu-sz  
await  svctm  %util

[root@localhost kernel]# iostat -x /dev/hda
Linux 2.4.4-ac9 (localhost.localdomain)         07/07/01

avg-cpu:  %user   %nice    %sys   %idle
           8.50    0.12    1.24   90.14
Device:  rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s avgrq-sz avgqu-sz  
await  svctm  %util

[root@localhost kernel]# iostat -x /dev/hda1
Linux 2.4.4-ac9 (localhost.localdomain)         07/07/01

avg-cpu:  %user   %nice    %sys   %idle
           8.50    0.12    1.24   90.14
Device:  rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s avgrq-sz avgqu-sz  
await  svctm  %util

[root@localhost kernel]# iostat -x hda1
Linux 2.4.4-ac9 (localhost.localdomain)         07/07/01

avg-cpu:  %user   %nice    %sys   %idle
           8.50    0.12    1.24   90.14
Device:  rrqm/s wrqm/s   r/s   w/s  rsec/s  wsec/s avgrq-sz avgqu-sz  
await  svctm  %util