Re: [Qemu-devel] [PATCH v2] qga: add systemd socket activation support

["Daniel P. Berrange" <berrange@redhat.com>]

On Fri, Jan 06, 2017 at 03:29:30PM +0000, Stefan Hajnoczi wrote:
> AF_UNIX and AF_VSOCK listen sockets can be passed in by systemd on
> startup.  This allows systemd to manage the listen socket until the
> first client connects and between restarts.  Advantages of socket
> activation are that parallel startup of network services becomes
> possible and that unused daemons do not consume memory.
> 
> The key to achieving this is the LISTEN_FDS environment variable, which
> is a stable ABI as shown here:
> https://www.freedesktop.org/wiki/Software/systemd/InterfacePortabilityAndStabilityChart/
> 
> We could link against libsystemd and use sd_listen_fds(3) but it's easy
> to implement the tiny LISTEN_FDS ABI so that qemu-ga does not depend on
> libsystemd.  Some systems may not have systemd installed and wish to
> avoid the dependency.  Other init systems or socket activation servers
> may implement the same ABI without systemd involvement.
> 
> Test as follows:
> 
>   $ cat ~/.config/systemd/user/qga.service
>   [Unit]
>   Description=qga
> 
>   [Service]
>   WorkingDirectory=/tmp
>   ExecStart=/path/to/qemu-ga --logfile=/tmp/qga.log --pidfile=/tmp/qga.pid --statedir=/tmp
> 
>   $ cat ~/.config/systemd/user/qga.socket
>   [Socket]
>   ListenStream=/tmp/qga.sock
> 
>   [Install]
>   WantedBy=default.target
> 
>   $ systemctl --user daemon-reload
>   $ systemctl --user start qga.socket
>   $ nc -U /tmp/qga.sock
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> v2:
>  * Drop libsystemd dependency [danpb]
> 
>  qga/channel.h       |  3 ++-
>  qga/channel-posix.c | 66 ++++++++++++++++++++++++++---------------------
>  qga/channel-win32.c |  2 +-
>  qga/main.c          | 74 +++++++++++++++++++++++++++++++++++++++++++++++++----
>  4 files changed, 109 insertions(+), 36 deletions(-)

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>



Regards,
Daniel
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