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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> Reviewed-by: Daniel P. Berrange <berrange@redhat.com> Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>
35 lines
964 B
C
35 lines
964 B
C
/*
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* QEMU Guest Agent channel declarations
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*
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* Copyright IBM Corp. 2012
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*
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* Authors:
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* Michael Roth <mdroth@linux.vnet.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#ifndef QGA_CHANNEL_H
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#define QGA_CHANNEL_H
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typedef struct GAChannel GAChannel;
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typedef enum {
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GA_CHANNEL_VIRTIO_SERIAL,
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GA_CHANNEL_ISA_SERIAL,
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GA_CHANNEL_UNIX_LISTEN,
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GA_CHANNEL_VSOCK_LISTEN,
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} GAChannelMethod;
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typedef gboolean (*GAChannelCallback)(GIOCondition condition, gpointer opaque);
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GAChannel *ga_channel_new(GAChannelMethod method, const gchar *path,
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int listen_fd, GAChannelCallback cb,
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gpointer opaque);
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void ga_channel_free(GAChannel *c);
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GIOStatus ga_channel_read(GAChannel *c, gchar *buf, gsize size, gsize *count);
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GIOStatus ga_channel_write_all(GAChannel *c, const gchar *buf, gsize size);
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#endif
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