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Michal Privoznik f3ab818984 rpc: Temporarily stop accept()-ing new clients on EMFILE 
This commit is related to 5de203f879 which I pushed a few days
ago. While that commit prioritized closing clients socket over
the rest of I/O process, this one goes one step further and
temporarily suspends processing new connection requests.

A brief recapitulation of the problem:

1) assume that libvirt is at the top of RLIMIT_NOFILE (that is no
   new FDs can be opened).

2) we have a client trying to connect to a UNIX/TCP socket

Because of 2) our event loop sees POLLIN on the socket and thus
calls virNetServerServiceAccept(). But since no new FDs can be
opened (because of 1)) the request is not handled and we will get
the same event on next iteration. The poll() will exit
immediately because there is an event on the socket.  Thus we end
up in an endless loop.

To break the loop and stop burning CPU cycles we can stop
listening for events on the socket and set up a timer tho enable
listening again after some time (I chose 5 seconds because of no
obvious reason).

There's another area where we play with temporarily suspending
accept() of new clients - when a client disconnects and we check
max_clients against number of current clients. Problem here is
that max_clients can be orders of magnitude larger than
RLIMIT_NOFILE but more importantly, what this code considers
client disconnect is not equal to closing client's FD.
A client disconnecting means that the corresponding client
structure is removed from the internal list of clients. Closing
of the client's FD is done from event loop - asynchronously.

To avoid this part stepping on the toes of my fix, let's make the
code NOP if socket timer (as described above) is active.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
 		2021-10-20 16:25:22 +02:00
.ctags.d maint: Add support for .ctags.d 2019-05-31 17:54:28 +02:00
.github/workflows Switch to new GitHub repo-lockdown configuration 2021-10-20 14:27:20 +01:00
.gitlab/issue_templates gitlab: Add disclaimer to the 'feature' issue template 2021-07-30 15:26:45 +02:00
build-aux virsh: Add wrapper for virStreamFree 2021-10-06 09:27:43 +02:00
ci ci: switch all non-released distros to be non-gating 2021-10-20 12:57:56 +01:00
docs virsh: Add QMP command wrapping for 'qemu-monitor-command' 2021-10-18 16:04:17 +02:00
examples qemu: Wire up MEMORY_DEVICE_SIZE_CHANGE event 2021-10-01 11:04:47 +02:00
include docs: describe flag VIR_STORAGE_POOL_CREATE_NORMAL to correct the HTML doc 2021-10-04 12:03:43 +00:00
po tools: add virt-host-validate-ch for ch driver 2021-10-12 17:28:35 +02:00
scripts scripts: include function versions in API definition 2021-09-23 16:30:18 +01:00
src rpc: Temporarily stop accept()-ing new clients on EMFILE 2021-10-20 16:25:22 +02:00
tests qemu: remove use of implicit boolean syntax for guest features 2021-10-20 13:19:49 +01:00
tools virsh: Add QMP command wrapping for 'qemu-monitor-command' 2021-10-18 16:04:17 +02:00
.color_coded.in gnulib: delete all gnulib integration 2020-02-07 15:03:54 +00:00
.ctags ctags: Generate tags for headers, i.e. function prototypes 2018-09-18 14:21:33 +02:00
.dir-locals.el build: avoid tabs that failed syntax-check 2012-09-06 09:43:46 -06:00
.editorconfig Add .editorconfig 2019-09-06 12:47:46 +02:00
.gitignore gitignore: Ignore __pycache__ directory 2021-03-22 12:05:11 +01:00
.gitlab-ci.yml gitlab: remove obsolete job rules for TEMPORARILY_DISABLED variable 2021-09-20 14:15:38 +01:00
.gitmodules gnulib: delete all gnulib integration 2020-02-07 15:03:54 +00:00
.gitpublish gitpublish: add a subject prefix 2020-01-16 13:04:11 +00:00
.mailmap mailmap: consolidate my email addresses 2020-10-06 12:05:09 +02:00
.ycm_extra_conf.py.in gnulib: delete all gnulib integration 2020-02-07 15:03:54 +00:00
AUTHORS.rst.in AUTHORS: Add myself to the list of commiters 2021-07-14 14:51:19 +02:00
CONTRIBUTING.rst meson: adjust our documentation to mention meson instead of autoconf 2020-08-03 09:27:09 +02:00
COPYING maint: follow recommended practice for using LGPL 2013-05-20 14:15:21 -06:00
COPYING.LESSER maint: Remove control characters from LGPL license file 2015-09-25 09:16:24 +02:00
NEWS.rst NEWS: Mention conversion of '-device' to JSON starting with QEMU-6.2 2021-10-18 14:00:59 +02:00
README.rst README: drop Travis CI badge 2020-08-03 15:08:28 +02:00
config.h meson: Declare GLIB_VERSION_* macros at configure 2021-05-03 12:08:26 +02:00
configmake.h.in meson: generate configmake.h 2020-08-03 09:26:48 +02:00
gitdm.config gitdm: add 'ibm' file 2019-10-18 17:32:52 +02:00
libvirt-admin.pc.in Add libvirt-admin library 2015-06-16 13:46:20 +02:00
libvirt-lxc.pc.in Add pkg-config files for libvirt-qemu & libvirt-lxc 2014-06-23 16:17:27 +01:00
libvirt-qemu.pc.in Add pkg-config files for libvirt-qemu & libvirt-lxc 2014-06-23 16:17:27 +01:00
libvirt.pc.in Add pkg-config files for libvirt-qemu & libvirt-lxc 2014-06-23 16:17:27 +01:00
libvirt.spec.in spec: change the ownership of cache directory 2021-10-12 16:54:49 +02:00
meson.build Post-release version bump to 7.9.0 2021-10-01 10:38:45 +02:00
meson_options.txt remote: switch to auto-spawn modular daemons by default 2021-06-18 17:13:15 +01:00
mingw-libvirt.spec.in rpm: fix mingw obsoletes lines 2021-08-02 13:47:20 +01:00
run.in run: set abs_builddir variables 2021-08-12 10:33:55 +02:00

README.rst 

.. image:: https://gitlab.com/libvirt/libvirt/badges/master/pipeline.svg
     :target: https://gitlab.com/libvirt/libvirt/pipelines
     :alt: GitLab CI Build Status
.. image:: https://bestpractices.coreinfrastructure.org/projects/355/badge
     :target: https://bestpractices.coreinfrastructure.org/projects/355
     :alt: CII Best Practices
.. image:: https://translate.fedoraproject.org/widgets/libvirt/-/libvirt/svg-badge.svg
     :target: https://translate.fedoraproject.org/engage/libvirt/
     :alt: Translation status

==============================
Libvirt API for virtualization
==============================

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.

For some of these hypervisors, it provides a stateful management
daemon which runs on the virtualization host allowing access to the
API both by non-privileged local users and remote users.

Layered packages provide bindings of the libvirt C API into other
languages including Python, Perl, PHP, Go, Java, OCaml, as well as
mappings into object systems such as GObject, CIM and SNMP.

Further information about the libvirt project can be found on the
website:

https://libvirt.org


License
=======

The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.0 (or later). See the files ``COPYING.LESSER``
and ``COPYING`` for full license terms & conditions.


Installation
============

Instructions on building and installing libvirt can be found on the website:

https://libvirt.org/compiling.html

Contributing
============

The libvirt project welcomes contributions in many ways. For most components
the best way to contribute is to send patches to the primary development
mailing list. Further guidance on this can be found on the website:

https://libvirt.org/contribute.html


Contact
=======

The libvirt project has two primary mailing lists:

* libvirt-users@redhat.com (**for user discussions**)
* libvir-list@redhat.com (**for development only**)

Further details on contacting the project are available on the website:

https://libvirt.org/contact.html