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- An 'xc_error' struct is used to pass around error details. Currently contains two members 'code' an enumeration of error types, and 'message' a free text description of the specific problem. - The xc_get_last_error() method returns a const pointer to the internal instance of this struct manged by libxc. By returning a const pointer we can add extra members to the end of the struct at any time without worrying about ABI of callers. This will let us provide more fine-grained info if needed in the future. - The xc_error instance is statically defined inside libxc and marked __thread. This ensures that errors are recorded per-thread, and that when dealing with errors we never need to call malloc - all storage needed is statically allocated. - The xc_clear_last_error() method resets any currently recorded error details - The xc_error_code_to_desc() method converts the integer error code into a generic user facing messsage. eg "Invalid kernel". Together with the 'message' field from xc_error, this provides the user visible feedback. eg "Invalid kernel: Non PAE-kernel on PAE host." - A callback can be registered with xc_set_error_handler to receive notification whenever an error is recorded, rather than querying for error details after the fact with xc_get_last_error - If built with -DDEBUG set, a default error handler will be registered which calls fprintf(stderr), thus maintaining current behaviour of logging errors to stderr during developer builds. - The python binding for libxc is updated to use xc_get_last_error to pull out error details whenever appropriate, instead of returning info based on 'errno' - The xc_set_error method is private to libxc internals, and is used for setting error details - The ERROR and PERROR macros have been updated to call xc_set_error automatically specifying XC_INTERNAL_ERROR as the error code. This gives a generic error report for all current failure points - Some uses of the ERROR macro have been replaced with explicit calls to xc_set_error to enable finer grained error reporting. In particular the code dealing with invalid kernel types uses this to report about PAE/architecture/wordsize mismatches The patch has been tested by calling xm create against a varietry of config files defining invalid kernels of various kinds. It has also been tested with libvirt talking to xend. In both cases the error messages were propagated all the way back up the stack. There is only one place where I need to do further work. The suspend & restore APIs in Xend invoke external helper programs rather than calling libxc directly. This means that error details are essentially lost. Since there is already code in XenD which scans STDERR from these programs I will investigate adapting this to extract actual error messages from these helpers. Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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http://www.xensource.com/xen/about.html
What is Xen?
============
Xen is a Virtual Machine Monitor (VMM) originally developed by the
Systems Research Group of the University of Cambridge Computer
Laboratory, as part of the UK-EPSRC funded XenoServers project. Xen
is freely-distributable Open Source software, released under the GNU
GPL. Since its initial public release, Xen has grown a large
development community, spearheaded by XenSource Inc, a company created
by the original Xen development team to build enterprise products
around Xen.
The 3.0 release offers excellent performance, hardware support and
enterprise-grade features such as x86_32-PAE, x86_64, SMP guests and
live relocation of VMs. This install tree contains source for a Linux
2.6 guest; ports to Linux 2.4, NetBSD, FreeBSD and Solaris will follow
later (and are already available for previous Xen releases).
This file contains some quick-start instructions to install Xen on
your system. For full documentation, see the Xen User Manual. If this
is a pre-built release then you can find the manual at:
dist/install/usr/share/doc/xen/pdf/user.pdf
If you have a source release, then 'make -C docs' will build the
manual at docs/pdf/user.pdf.
Quick-Start Guide - Pre-Built Binary Release
============================================
[NB. Unless noted otherwise, all the following steps should be
performed with root privileges.]
1. Install the binary distribution onto your filesystem:
# sh ./install.sh
Among other things, this will install Xen and Xen-ready Linux
kernel files in /boot, kernel modules and Python packages in /lib,
and various control tools in standard 'bin' directories.
2. Configure your bootloader to boot Xen and an initial Linux virtual
machine. Note that Xen currently only works with GRUB and pxelinux
derived boot loaders: less common alternatives such as LILO are
*not* supported. You can most likely find your GRUB menu file at
/boot/grub/menu.lst: edit this file to include an entry like the
following:
title Xen 3.0 / XenLinux 2.6
kernel /boot/xen-3.0.gz console=vga
module /boot/vmlinuz-2.6-xen root=<root-dev> ro console=tty0
module /boot/initrd-2.6-xen.img
NB: Not all kernel configs need an initial ram disk (initrd), but
if you do specify one you'll need to use the 'module' grub directive
rather than 'initrd'.
The linux command line takes all the usual options, such as
root=<root-dev> to specify your usual root partition (e.g.,
/dev/hda1).
The Xen command line takes a number of optional arguments described
in the manual. The most common is 'dom0_mem=xxxM' which sets the
amount of memory to allocate for use by your initial virtual
machine (known as domain 0). Note that Xen itself reserves about
32MB memory for internal use, which is not available for allocation
to virtual machines.
3. Reboot your system and select the "Xen 3.0 / XenLinux 2.6" menu
option. After booting Xen, Linux will start and your initialisation
scripts should execute in the usual way.
Quick-Start Guide - Source Release
==================================
First, there are a number of prerequisites for building a Xen source
release. Make sure you have all the following installed, either by
visiting the project webpage or installing a pre-built package
provided by your Linux distributor:
* GCC (preferably v3.2.x or v3.3.x; older versions are unsupported)
* GNU Make
* GNU Binutils
* Development install of zlib (e.g., zlib-dev)
* Development install of Python v2.3 or later (e.g., python-dev)
* Development install of curses (e.g., libncurses-dev)
* bridge-utils package (/sbin/brctl)
* iproute package (/sbin/ip)
* hotplug or udev
[NB. Unless noted otherwise, all the following steps should be
performed with root privileges.]
1. Download and untar the source tarball file. This will be a
file named xen-unstable-src.tgz, or xen-$version-src.tgz.
You can also pull the current version from the SCMS
that is being used (Bitkeeper, scheduled to change shortly).
# tar xzf xen-unstable-src.tgz
Assuming you are using the unstable tree, this will
untar into xen-unstable. The rest of the instructions
use the unstable tree as an example, substitute the
version for unstable.
2. cd to xen-unstable (or whatever you sensibly rename it to).
The Linux, netbsd and freebsd kernel source trees are in
the $os-$version-xen-sparse directories.
On Linux:
3. For the very first build, or if you want to destroy existing
.configs and build trees, perform the following steps:
# make world
# make install
This will create and install onto the local machine. It will build
the xen binary (xen.gz), and a linux kernel and modules that can be
used in both dom0 and an unprivileged guest kernel (vmlinuz-2.6.x-xen),
the tools and the documentation.
You can override the destination for make install by setting DESTDIR
to some value.
The make command line defaults to building the kernel vmlinuz-2.6.x-xen.
You can override this default by specifying KERNELS=kernelname. For
example, you can make two kernels - linux-2.6-xen0
and linux-2.6-xenU - which are smaller builds containing only selected
modules, intended primarily for developers that don't like to wait
for a full -xen kernel to build. The -xenU kernel is particularly small,
as it does not contain any physical device drivers, and hence is
only useful for guest domains.
To make these two kernels, simply specify
KERNELS="linux-2.6-xen0 linux-2.6-xenU"
in the make command line.
If you want to build an x86_32 PAE capable xen and kernel to work
on machines with >= 4GB of memory, use XEN_TARGET_X86_PAE=y on the
make command line.
4. To rebuild an existing tree without modifying the config:
# make dist
This will build and install xen, kernels, tools, and
docs into the local dist/ directory.
You can override the destination for make install by setting DISTDIR
to some value.
make install and make dist differ in that make install does the
right things for your local machine (installing the appropriate
version of hotplug or udev scripts, for example), but make dist
includes all versions of those scripts, so that you can copy the dist
directory to another machine and install from that distribution.
5. To rebuild a kernel with a modified config:
# make linux-2.6-xen-config CONFIGMODE=menuconfig (or xconfig)
# make linux-2.6-xen-build
# make linux-2.6-xen-install
Depending on your config, you may need to use 'mkinitrd' to create
an initial ram disk, just like a native system e.g.
# depmod 2.6.16-xen
# mkinitrd -v -f --with=aacraid --with=sd_mod --with=scsi_mod initrd-2.6.16-xen.img 2.6.16-xen