Xen users - Jun 2005 - max_loop device problem

Hi all,

Hope you are all doing well...

I had a problem on creating 9th domain in my system.

I am using Cent-OS 3.4 and xen-2.0.6..   Obviously it''s a loop back 
device mount issue. I have my grub.conf entry as follows

title Xen-2.6
  root (hd0,0)
  kernel /xen.gz dom0_mem=65536
  module /vmlinuz-2.6.11.10-xen0 root=/dev/hda6 ro console=tty0 max_loop=256

ls -l /dev/loop*

brw-rw----    1 root     disk       7,   0 Sep  9  2004 /dev/loop0
brw-rw----    1 root     disk       7,   1 Sep  9  2004 /dev/loop1
brw-rw----    1 root     disk       7,  10 Sep  9  2004 /dev/loop10
brw-rw----    1 root     disk       7,  11 Sep  9  2004 /dev/loop11
brw-rw----    1 root     disk       7,  12 Sep  9  2004 /dev/loop12
brw-rw----    1 root     disk       7,  13 Sep  9  2004 /dev/loop13
brw-rw----    1 root     disk       7,  14 Sep  9  2004 /dev/loop14
brw-rw----    1 root     disk       7,  15 Sep  9  2004 /dev/loop15
brw-rw----    1 root     disk       7,   2 Sep  9  2004 /dev/loop2
brw-rw----    1 root     disk       7,   3 Sep  9  2004 /dev/loop3
brw-rw----    1 root     disk       7,   4 Sep  9  2004 /dev/loop4
brw-rw----    1 root     disk       7,   5 Sep  9  2004 /dev/loop5
brw-rw----    1 root     disk       7,   6 Sep  9  2004 /dev/loop6
brw-rw----    1 root     disk       7,   7 Sep  9  2004 /dev/loop7
brw-rw----    1 root     disk       7,   8 Sep  9  2004 /dev/loop8
brw-r--r--    1 root     root       7,   9 Jun 25 21:00 /dev/loop9

I created a sparse filesystem and tried to mount that on loop back device

[root@guava looptest]# mount -o loop  root_fs loop1/
mount: could not find any free loop device

[root@guava looptest]# mount -o loop=/dev/loop9  root_fs loop1/
ioctl: LOOP_SET_FD: Device or resource busy

Can anybody help me to sort out this issue.... We have another system 
with cent-OS 3.5 with only 3 domains. I tested that server by creating 
10 filesystems  and mounting them on loop back devices and found no 
problem on mounting more that 8. I also tested that with a fedora-core3 
machine and found no problem. So in this situation what is likely to be 
haunting this machine... I need a quick a reply since we are using xen 
in a production environment...

Thanks once again
Sadique

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> title Xen-2.6
>   root (hd0,0)
>   kernel /xen.gz dom0_mem=65536
>   module /vmlinuz-2.6.11.10-xen0 root=/dev/hda6 ro console=tty0
> max_loop=256
That looks OK but I guess 256 might be too high.  IIRC, the loop driver 
handles a maximum of 100 devices, or so.  Try reducing it to something like 
32, 64, etc and see if that helps.

You have compiled loop support statically into the kernel, right?  If
it''s in
a module, you''ll need to pass it as a module parameter instead.
> brw-r--r--    1 root     root       7,   9 Jun 25 21:00 /dev/loop9
Why does this one have different permissions to the other ones?  (not that it 
should matter, but all the same...)
> I created a sparse filesystem and tried to mount that on loop back device
>
> [root@guava looptest]# mount -o loop  root_fs loop1/
> mount: could not find any free loop device
Weird.
> [root@guava looptest]# mount -o loop=/dev/loop9  root_fs loop1/
> ioctl: LOOP_SET_FD: Device or resource busy
Sanity check: Have you tried loop10, etc...?  Do they all give this error?
> haunting this machine... I need a quick a reply since we are using xen
> in a production environment...
If the above don''t help, can you rebuild the kernel and statically
configure a
higher number of loop devs (say, 32), then reboot dom0?

Cheers,
Mark

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