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Re: [Xen-devel] [PATCH] Introduce dom0-min-space configuration option
On 07/13/2010 08:02 PM, Ian Jackson wrote:
Michal Novotny writes ("[Xen-devel] [PATCH] Introduce dom0-min-space configuration
This is the patch to introduce configuration option called
dom0-min-space since there were some issues with data inflation
because of invalid input data stream for zlib decompression.
The issue occured because of insufficient free space on the dom0 so
this patch checks the free available space for /var/lib/xen
and refuses to start up any guests when the space is below
specified value. Setting up the value to 0 disables the check
which preserves the behaviour before this patch applied and
this is the default value for this option.
Thanks for the patch, but I'm not sure I entirely follow.
What "issues with data inflation because of invalid input data stream
for zlib decompression" were there and how do they relate to lack of
space on /var/lib/xen ?
Ian, the problem is when pygrub extracts the vmlinuz and initrd for PV
guests but there's insufficient space on the dom0, there's no error
message but the error is being raised from Xend itself, libxc to be
precise since there's the zStream inflation code but since the input
data are not valid (i.e. they're just partial, let's say only 50 KiB was
extracted to /var/lib/xen since after those 50 KiBs the dom0 had no
space available) the zStream (zlib decompression) fails with Z_BUF_ERROR
and then it outputs annoying and nothing saying message to standalone
users (non-developers) to doesn't do investigation on their own. This
patch would prevent going into those issues since there would be always
at least specified amount of free space available for PV images to be
extracted to /var/lib/xen .
Is this just for the situation where the dom0 filesystem hasn't enough
space to contain the uncompressed version of the domU kernel and
initrd which are to be loaded ?
Well, this is for compressed version being extracted from the guest
image files. This is being saved to /var/lib/xen and if there's not
enough space to save it the deflation fails with -5 (Z_BUF_ERROR) which
says nothing to standalone users.
Your patch just raises an error. Why does the situation in which the
patch is needed not already raise an appropriate error ? Perhaps it
would be better to arrange that it does.
Well, the reason is that there should be multiple reasons that could
make the decompression (gunzip) fail. Also, having the dom0 with no
space could cause some other (non-Xen) related errors so having this
option could prevent user running into those issues - mainly if the
user's saving images to the default location, i.e. /var/lib/xen/images,
he/she can get running out of free space on dom0 very easily.
Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat
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