Re: [Xen-devel] [PATCH 0/3] domUloader

[Anthony Liguori <aliguori@xxxxxxxxxx>]

Hi Kurt,

Kurt Garloff wrote:

> domUloader parses the bootentry (passed via --entry=) and the disk
> setup (passed via --disks=). It then sets up loop devices as needed,
> scans for partition tables (the exported disks / loop devs can
> contain partitions) using kpartx (dm) and sets them up, so the kernel
> and initrd can be copied to a temporary location in dom0. 
>  
Just to clarify, this means that domU filesystems are being mounted in 
dom0?  I knew there was some security concerns voiced about this many 
months ago.  I think one of the advantages to using libext2 was that it 
theoritically allowed the filesystem parsing to be done as a 
non-privileged user.
Regards,

Anthony Liguori

> The bootentry may contain a dev: prefix describing the partition
> (from a domU perspective!) where kernel and initrd are located,
> followed by kernel filename and (optional) initrd filenames relative
> to the filesystem on dev:.
> The kernel and initrd filename can also be relative to the domU root
> filesystem. The domUloader than evaluates /etc/fstab found in the
> root filesystem (passed via --root=) to locate kernel and initrd.
> Afterwards everything is cleaned up. (We use the destructors, so
> python reference counting makes sure this also happens when
> exceptions occur.)
>
> Unlike pygrub, it does use any code to understand filesystems or
> partitions; the filesystem support comes from the dom0 kernel,
> whereas kpartx (from multipath-tools) is used for the knowledge
> of partitions and for setting up device-mapper.
>
> More details by calling domUloader.py --help.
>
> An example config could look like this:
> bootentry = hda2:/vmlinuz-xen,/initrd-xen
> bootloader = /path/to/domUloader.py
> disks = ['phy:VG_Xen/LV_dom5,hda,w', 'file:/var/lib/xen/test,sda,w']
> ...
> assuming LV_dom5 has a second partition with a filesystem containing
> vmlinuz-xen and initrd-xen in its root fs (the /boot partition).
>
> or 
> bootentry = /boot/vmlinuz-xen,/boot/initrd-xen
> bootloader = /path/to/domUloader.py
> root = /dev/hda1
> disk = ...
> assuming that the root filesystem has an /etc/fstab that points the
> way to /boot/vmlinuz-xen. (Does not need to be a separate FS.)
>
> The following three mails will contain 
> (1) A patch to xend/XenDomainInfo.py, xend/XenBootloader.py and 
>    xm/create.py, making sure that all the needed info is passed
>    to the bootloader and also stored for reuse on rebooting.
> (2) A patch to make pygrub accept the new parameters passed by
>    XendBootloader.py (but so far pygrub just ignores them ...)
> (3) The domUloader.py script.
>
>
> Patches are against a working copy (8259) on my laptop; if noone
> else will, I can create diffs against mercurial tip.
>
> I hope this is useful to someone and can be integrated into the
> Xen distribution.
>
> Enjoy,
>  
>
> ------------------------------------------------------------------------
>
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>  

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