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Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.
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Laine Stump 595e26c086 qemu: drop driver lock while trying to terminate qemu process 
This patch is based on an earlier patch by Eric Blake which was never
committed:

https://www.redhat.com/archives/libvir-list/2011-November/msg00243.html

Aside from rebasing, this patch only drops the driver lock once (prior
to the first time the function sleeps), then leaves it dropped until
it returns (Eric's patch would drop and re-acquire the lock around
each call to sleep).

At the time Eric sent his patch, the response (from Dan Berrange) was
that, while it wasn't a good thing to be holding the driver lock while
sleeping, we really need to rethink locking wrt the driver object,
switching to a finer-grained approach that locks individual items
within the driver object separately to allow for greater concurrency.

This is a good plan, and at the time it made sense to not apply the
patch because there was no known bug related to the driver lock being
held in this function.

However, we now know that the length of the wait in qemuProcessKill is
sometimes too short to allow the qemu process to fully flush its disk
cache before SIGKILL is sent, so we need to lengthen the timeout (in
order to improve the situation with management applications until they
can be updated to use the new VIR_DOMAIN_DESTROY_GRACEFUL flag added
in commit 72f8a7f197). But, if we
lengthen the timeout, we also lengthen the amount of time that all
other threads in libvirtd are essentially blocked from doing anything
(since just about everything needs to acquire the driver lock, if only
for long enough to get a pointer to a domain).

The solution is to modify qemuProcessKill to drop the driver lock
while sleeping, as proposed in Eric's patch. Then we can increase the
timeout with a clear conscience, and thus at least lower the chances
that someone running with existing management software will suffer the
consequence's of qemu's disk cache not being flushed.

In the meantime, we still should work on Dan's proposal to make
locking within the driver object more fine grained.

(NB: although I couldn't find any instance where qemuProcessKill() was
called with no jobs active for the domain (or some other guarantee
that the current thread had at least one refcount on the domain
object), this patch still follows Eric's method of temporarily adding
a ref prior to unlocking the domain object, because I couldn't
convince myself 100% that this was the case.)
2012-02-15 13:57:10 -05:00
.gnulib@e9e8aba12a Update gnulib to fix mingw64 compilation errors 2012-02-01 17:37:45 -07:00
daemon Allow polkit auth for VNC and SSH users 2012-02-07 11:59:35 -05:00
docs Install API XML desc to a standard location 2012-02-14 16:42:02 +00:00
examples maint: consolidate several .gitignore files 2012-02-03 15:27:16 -07:00
gnulib build: update to latest gnulib 2012-01-12 15:47:54 -07:00
include maint: consolidate several .gitignore files 2012-02-03 15:27:16 -07:00
m4 build: silence some compiler warnings from gnulib 2012-01-19 13:14:10 -07:00
po Release of libvirt-0.9.10 2012-02-13 22:31:31 +08:00
python python: make other APIs share common {get, set}PyVirTypedParameter 2012-02-10 17:17:18 -07:00
src qemu: drop driver lock while trying to terminate qemu process 2012-02-15 13:57:10 -05:00
tests Revert "qemu: add ibmvscsi controller model" 2012-02-13 21:37:03 +08:00
tools qemu: make block io tuning smarter 2012-02-13 10:34:25 -07:00
.dir-locals.el maint: let emacs avoid tabs in rng files 2011-08-13 08:56:26 -06:00
.gitignore maint: Add test output files to .gitignore 2012-02-06 18:27:40 +01:00
.gitmodules make .gnulib a submodule 2009-07-08 16:17:51 +02:00
.mailmap maint: prune duplicate listings in AUTHORS 2012-02-03 09:56:45 -07:00
AUTHORS Update myself in AUTHORS 2012-02-06 23:39:18 +08:00
autobuild.sh Disable python explicitly in mingw32 autobuild 2011-12-19 13:44:18 +00:00
autogen.sh build: allow for local gnulib diffs 2011-11-09 09:03:33 -07:00
bootstrap Update gnulib to fix mingw64 compilation errors 2012-02-01 17:37:45 -07:00
bootstrap.conf Replace hashing algorithm with murmurhash 2012-01-26 14:18:53 +00:00
cfg.mk python: use libvirt_util to avoid raw free 2012-02-03 10:41:47 -07:00
ChangeLog-old virterror.c: Fix several spelling mistakes 2012-02-03 11:32:51 -07:00
configure.ac Release of libvirt-0.9.10 2012-02-13 22:31:31 +08:00
COPYING.LIB remove all trailing blank lines 2009-07-16 15:06:42 +02:00
HACKING Document STREQ_NULLABLE and STRNEQ_NULLABLE 2011-10-06 16:50:38 +02:00
libvirt.pc.in Fix typos in API XML file paths 2012-02-15 11:29:38 +00:00
libvirt.spec.in Fix typos in API XML file paths 2012-02-15 11:29:38 +00:00
Makefile.am maint: add missing copyright notices 2011-07-28 15:01:17 -06:00
Makefile.nonreentrant Ban use of all inet_* functions 2010-10-22 11:59:23 +01:00
mingw32-libvirt.spec.in Fix typos in API XML file paths 2012-02-15 11:29:38 +00:00
README Correct typos in the documentation (Atsushi SAKAI) 2008-01-24 10:15:13 +00:00
README-hacking maint: relax git minimum version 2010-02-24 14:29:27 -05:00
TODO Update todo list file to point at bugzilla/website 2010-10-13 16:45:26 +01:00

README 

         LibVirt : simple API for virtualization

  Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.

Daniel Veillard <veillard@redhat.com>