mirror of
https://github.com/xen-project/xen.git
synced 2026-10-28 02:01:24 +01:00
Ian Jackson
5a533d0ba5
If the application calls libxl with ao_how==0 and also makes calls
like _occurred, libxl will sometimes get stuck.
The bug happens as follows (for example):
Thread A
libxl_do_thing(,ao_how==0)
libxl_do_thing starts, sets up some callbacks
libxl_do_thing exit path calls AO_INPROGRESS
libxl__ao_inprogress goes into event loop
eventloop_iteration sleeps on:
- do_thing's current fd set
- sigchld pipe if applicable
- its poller
Thread B
libxl_something_occurred
the something is to do with do_thing, above
do_thing_next_callback does some more work
do_thing_next_callback becomes interested in fd N
thread B returns to application
Note that nothing wakes up thread A. A is not listening on fd N. So
do_thing_* will not spot when fd N signals. do_thing will not make
further timely progress. If there is no timeout thread A will never
wake up.
The problem here occurs because thread A is waiting on an out of date
osevent set.
There is also the possibility that a thread might block waiting for
libxl osevents but outside libxl, eg if the application used
libxl_osevent_beforepoll. We will deal with that in a moment.
See the big comment in libxl_event.c for a fairly formal correctness
argument.
This depends on libxl__egc_ao_cleanup_1_baton being called everywhere
an egc or ao is disposed of. Firstly egcs: in this patch we rename
libxl__egc_cleanup, which means we catch all the disposal sites.
Secondly aos: these are disposed of by (i) AO_CREATE_FAIL
(ii) ao__inprogress and (iii) an event which completes the ao later.
(i) and (ii) we handle by adding the call to _baton. In the case of
(iii) any such function must be an event-generating function so it has
an egc too, so it will pass on the baton when the egc is disposed.
Reported-by: George Dunlap <george.dunlap@citrix.com>
Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>
Tested-by: George Dunlap <george.dunlap@citrix.com>
---
v2: Call libxl__egc_ao_cleanup_1_baton (renamed from __egc_cleanup) on
all exits from ao_inprogress, even requests for async processing.
Fixes a remaining instance of this bug (!)
This involves disposing of ao->poller somewhat earlier.
v2: New correctness arguments in libxl_event.c comment and
in commit message.
#################################
_ _ _ _ _ _ _ _
| || | / | || | _ _ _ __ ___| |_ __ _| |__ | | ___
| || |_ | | || |_ _____| | | | '_ \/ __| __/ _` | '_ \| |/ _ \
|__ _|| |__ _|_____| |_| | | | \__ \ || (_| | |_) | | __/
|_|(_)_| |_| \__,_|_| |_|___/\__\__,_|_.__/|_|\___|
#################################
http://www.xen.org/
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 xen.org (http://www.xen.org).
This file contains some quick-start instructions to install Xen on
your system. For more information see http:/www.xen.org/ and
http://wiki.xen.org/
Quick-Start Guide
=================
First, this is just a quick-start guide. For more comprehensive
information see the INSTALL file and the Xen wiki at
http://wiki.xenproject.org and in particular
http://wiki.xenproject.org/wiki/Getting_Started.
Second, 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 OS distributor:
* GNU Make v3.80 or later
* C compiler and linker:
- For x86:
- GCC 4.1.2_20070115 or later
- GNU Binutils 2.16.91.0.5 or later
or
- Clang/LLVM 3.5 or later
- For ARM:
- GCC 4.8 or later
- GNU Binutils 2.24 or later
* Development install of zlib (e.g., zlib-dev)
* Development install of Python 2.6 or later (e.g., python-dev)
* Development install of curses (e.g., libncurses-dev)
* Development install of openssl (e.g., openssl-dev)
* Development install of x11 (e.g. xorg-x11-dev)
* Development install of uuid (e.g. uuid-dev)
* Development install of yajl (e.g. libyajl-dev)
* Development install of libaio (e.g. libaio-dev) version 0.3.107 or
greater.
* Development install of GLib v2.0 (e.g. libglib2.0-dev)
* Development install of Pixman (e.g. libpixman-1-dev)
* pkg-config
* bridge-utils package (/sbin/brctl)
* iproute package (/sbin/ip)
* GNU bison and GNU flex
* GNU gettext
* ACPI ASL compiler (iasl)
* Libc multiarch package (e.g. libc6-dev-i386 / glibc-devel.i686).
Required when building on a 64-bit platform to build
32-bit components which are enabled on a default build.
In addition to the above there are a number of optional build
prerequisites. Omitting these will cause the related features to be
disabled at compile time:
* Development install of Ocaml (e.g. ocaml-nox and
ocaml-findlib). Required to build ocaml components which
includes the alternative ocaml xenstored.
* cmake (if building vtpm stub domains)
* pandoc, transfig, pod2{man,html,text} for rendering various pieces of
documentation into alternative formats
* figlet (for generating the traditional Xen start of day banner)
* systemd daemon development files
* Development install of libnl3 (e.g., libnl-3-200,
libnl-3-dev, etc). Required if network buffering is desired
when using Remus with libxl. See docs/README.remus for detailed
information.
* 16-bit x86 assembler, loader and compiler for qemu-traditional / rombios
(dev86 rpm or bin86 & bcc debs)
* Development install of liblzma for rombios
Second, you need to acquire a suitable kernel for use in domain 0. If
possible you should use a kernel provided by your OS distributor. If
no suitable kernel is available from your OS distributor then refer to
http://wiki.xen.org/wiki/XenDom0Kernels for suggestions for
suitable kernels to use.
If you are looking to compile a Dom0 kernel from source, please refer to
http://wiki.xen.org/wiki/XenParavirtOps.
[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 git or mercurial
repositories at http://xenbits.xen.org/
# 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).
3. For the very first build, or if you want to destroy build trees,
perform the following steps:
# ./configure
# make world
# make install
See the documentation in the INSTALL file for more info.
This will create and install onto the local machine. It will build
the xen binary (xen.gz), the tools and the documentation.
You can override the destination for make install by setting DESTDIR
to some value.
4. To rebuild an existing tree without modifying the config:
# make dist
This will build and install xen, 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 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.
xenstore: xenstored and oxenstored
====================================
Xen uses a configuration database called xenstore [0] to maintain configuration
and status information shared between domains. A daemon is implemented as part
of xenstore to act as an interface for access to the database for dom0 and
guests. Two xenstored daemons are supported, one written in C which we refer
to as the xenstored (sometimes referred to as cxenstored), and another written
in Ocaml called oxenstored. Details for xenstore and the different
implementations can be found on the wiki's xenstore reference guide [1] and
the xenstored [2] page. You can choose which xenstore you want to enable as
default on a system through configure:
./configure --with-xenstored=xenstored
./configure --with-xenstored=oxenstored
By default oxenstored will be used if the ocaml development tools are found.
If you enable oxenstored the xenstored will still be built and installed,
the xenstored used can be changed through the configuration file:
/etc/sysconfig/xencommons
or
/etc/default/xencommons
You can change the preferred xenstored you want to use in the configuration
but since we cannot stop the daemon a reboot will be required to make the
change take effect.
[0] http://wiki.xen.org/wiki/XenStore
[1] http://wiki.xen.org/wiki/XenStoreReference
[2] http://wiki.xen.org/wiki/Xenstored
Python Runtime Libraries
========================
Various tools, such as pygrub, have the following runtime dependencies:
* Python 2.6 or later.
URL: http://www.python.org/
Debian: python
Note that the build system expects `python` to be available. If your system
only has `python2` or `python3` but not `python` (as in Linux From Scratch),
you will need to create a symlink for it, or specify PYTHON= when invoking
make, like (note the position of PYTHON= matters):
# make PYTHON=/usr/bin/python3
Intel(R) Trusted Execution Technology Support
=============================================
Intel's technology for safer computing, Intel(R) Trusted Execution Technology
(Intel(R) TXT), defines platform-level enhancements that provide the building
blocks for creating trusted platforms. For more information, see
http://www.intel.com/technology/security/.
Intel(R) TXT support is provided by the Trusted Boot (tboot) module in
conjunction with minimal logic in the Xen hypervisor.
Tboot is an open source, pre- kernel/VMM module that uses Intel(R) TXT to
perform a measured and verified launch of an OS kernel/VMM.
The Trusted Boot module is available from
http://sourceforge.net/projects/tboot. This project hosts the code in a
mercurial repo at http://tboot.sourceforge.net/hg/tboot.hg and contains
tarballs of the source. Instructions in the tboot README describe how
to modify grub.conf to use tboot to launch Xen.