Re: [Xen-users] Can't boot from ISO image...

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Hmmm...tap:aio you say....I'm googling it....can you reccomend a link
> to some description and/or explanation of tap:aio?

Not off the top of my head.

Basically, the file:/ syntax uses the loop device, as you know, which has a 
number of drawbacks (including easily running out of loop devices and some 
performance / memory use problems - particularly if you use a file: device on 
an NFS filesystem, which is a really good way of making the OOM killer come 
and attack your processes.)

tap:aio: uses the blocktap driver, which is Xen's userspace driver (with a 
kernelspace portion) for providing access to file-backed VBDs.  The aim of it 
is to give decent performance whilst mitigating the drawbacks of using the 
loopback device.  It also has greater flexibility because blocktap can 
support other VBD formats (e.g. tap:qcow for copy on write disks, although 
I'm not sure what Xen releases that's available in).

I'm not clear what your problem could be, but I'm thinking that tap:aio: may 
help sidestep it, or cast more light on the root cause.

HOWEVER

Regarding your file: problem, I've just had a brainwave.  Do you have SELinux 
enabled?  If so you need to have your ISO under /var/lib/xen/images or it'll 
probably fail to work correctly.  You'll probably find messages about SELinux 
preventing Xend / Xen hotplug scripts from performing the setup operations, 
if you look in /var/log/messages.

Cheers,
Mark

> thanks
>
> M
>
> On Jan 24, 2008 7:38 PM, Mark Williamson <mark.williamson@xxxxxxxxxxxx> 
wrote:
> > Do you really need to pass the ISO as a file:/ disk anyhow?  tap:aio is
> > supposed to be better and maybe it'll solve your problem into the
> > bargain!
> >
> > Cheers,
> > Mark
> >
> > On Thursday 24 January 2008, Lionel Kernux wrote:
> > > Hi,
> > >
> > > I've been trying to boot from a RHEL4 install iso without much luck
> > > (the xen way).
> > > The Host is:
> > > RHEL 5.1
> > > xen-3.0.3-41.el5
> > >
> > > Here is my guest config:
> > >
> > > #  -*- mode: python; -*-
> > > #======================================================================
> > >==== == # Python configuration setup for 'xm create'.
> > > # This script sets the parameters used when a domain is created using
> > > 'xm create'.
> > > # You use a separate script for each domain you want to create, or
> > > # you can set the parameters for the domain on the xm command line.
> > > #======================================================================
> > >==== ==
> > >
> > > import os, re
> > > arch = os.uname()[4]
> > > if re.search('64', arch):
> > >     arch_libdir = 'lib64'
> > > else:
> > >     arch_libdir = 'lib'
> > > kernel = "/usr/lib/xen/boot/hvmloader"
> > > builder='hvm'
> > > memory = 1536
> > > shadow_memory = 8
> > > name = "symbiosis"
> > > pae=1
> > > vif = [ 'type=ioemu, bridge=xenbr0' ]
> > > disk = [
> > > 'file:/var/lib/xen/images/symbiosis.img,ioemu:hda,w','file:/root/RHEL4.
> > >6-x8 6_64-AS-disc1.iso,ioemu:hdc:cdrom,r' ]
> > > device_model = '/usr/' + arch_libdir + '/xen/bin/qemu-dm'
> > > boot="d"
> > > vncunused=0
> > > vncconsole=1
> > > vncpasswd='secret'
> > > stdvga=0
> > > serial='pty'
> > > usb=1
> > > usbdevice='mouse'
> > >
> > > I run "xm create symbiosis" and get:
> > >
> > > Error: Device 5632 (vbd) could not be connected. losetup -r /dev/loop0
> > > /root/RHEL4.6-x86_64-AS-disc1.iso failed
> > >
> > > But, I can manually attach the loop device like so:
> > >
> > > losetup -r /dev/loop# /root/RHEL4.6-x86_64-AS-disc1.iso
> > >
> > > No problem.
> > >
> > > If I do:
> > >
> > > losetup -r /dev/loop5 /root/RHEL4.6-x86_64-AS-disc1.iso
> > >
> > > and then in the config file use this:
> > >
> > > disk = [
> > > 'file:/var/lib/xen/images/symbiosis.img,ioemu:hda,w','phy:/dev/loop5,io
> > >emu: hdc:cdrom,r' ]
> > >
> > > It boots off the ISO.
> > >
> > > Yes, it seems I can fake it out, but I'd like to get it work
> > > properly....
> > >
> > > Any help?
> > >
> > > Thanks
> > >
> > > M
> > >
> > > _______________________________________________
> > > Xen-users mailing list
> > > Xen-users@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-users
> >
> > --
> > Push Me Pull You - Distributed SCM tool
> > (http://www.cl.cam.ac.uk/~maw48/pmpu/)



-- 
Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/)

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