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@@ -77,6 +77,106 @@ When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP
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connections can be redirected from the host to the guest. It allows for
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connections can be redirected from the host to the guest. It allows for
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example to redirect X11, telnet or SSH connections.
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example to redirect X11, telnet or SSH connections.
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+Using passt as the user mode network stack
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+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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+
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+passt_ can be used as a simple replacement for SLIRP (``-net user``).
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+passt doesn't require any capability or privilege. passt has
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+better performance than ``-net user``, full IPv6 support and better security
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+as it's a daemon that is not executed in QEMU context.
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+
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+passt can be connected to QEMU either by using a socket
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+(``-netdev stream``) or using the vhost-user interface (``-netdev vhost-user``).
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+See `passt(1)`_ for more details on passt.
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+
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+.. _passt: https://passt.top/
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+.. _passt(1): https://passt.top/builds/latest/web/passt.1.html
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+
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+To use socket based passt interface:
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+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+
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+Start passt as a daemon::
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+
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+ passt --socket ~/passt.socket
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+
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+If ``--socket`` is not provided, passt will print the path of the UNIX domain socket QEMU can connect to (``/tmp/passt_1.socket``, ``/tmp/passt_2.socket``,
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+...). Then you can connect your QEMU instance to passt:
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+
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+.. parsed-literal::
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+ |qemu_system| [...OPTIONS...] -device virtio-net-pci,netdev=netdev0 -netdev stream,id=netdev0,server=off,addr.type=unix,addr.path=~/passt.socket
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+
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+Where ``~/passt.socket`` is the UNIX socket created by passt to
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+communicate with QEMU.
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+
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+To use vhost-based interface:
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+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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+
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+Start passt with ``--vhost-user``::
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+
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+ passt --vhost-user --socket ~/passt.socket
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+
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+Then to connect QEMU:
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+
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+.. parsed-literal::
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+ |qemu_system| [...OPTIONS...] -m $RAMSIZE -chardev socket,id=chr0,path=~/passt.socket -netdev vhost-user,id=netdev0,chardev=chr0 -device virtio-net,netdev=netdev0 -object memory-backend-memfd,id=memfd0,share=on,size=$RAMSIZE -numa node,memdev=memfd0
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+
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+Where ``$RAMSIZE`` is the memory size of your VM ``-m`` and ``-object memory-backend-memfd,size=`` must match.
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+
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+Migration of passt:
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+^^^^^^^^^^^^^^^^^^^
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+
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+When passt is connected to QEMU using the vhost-user interface it can
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+be migrated with QEMU and the network connections are not interrupted.
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+
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+As passt runs with no privileges, it relies on passt-repair to save and
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+load the TCP connections state, using the TCP_REPAIR socket option.
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+The passt-repair helper needs to have the CAP_NET_ADMIN capability, or run as root. If passt-repair is not available, TCP connections will not be preserved.
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+
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+Example of migration of a guest on the same host
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+________________________________________________
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+
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+Before being able to run passt-repair, the CAP_NET_ADMIN capability must be set
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+on the file, run as root::
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+
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+ setcap cap_net_admin+eip ./passt-repair
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+
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+Start passt for the source side::
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+
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+ passt --vhost-user --socket ~/passt_src.socket --repair-path ~/passt-repair_src.socket
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+
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+Where ``~/passt-repair_src.socket`` is the UNIX socket created by passt to
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+communicate with passt-repair. The default value is the ``--socket`` path
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+appended with ``.repair``.
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+
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+Start passt-repair::
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+
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+ passt-repair ~/passt-repair_src.socket
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+
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+Start source side QEMU with a monitor to be able to send the migrate command:
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+
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+.. parsed-literal::
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+ |qemu_system| [...OPTIONS...] [...VHOST USER OPTIONS...] -monitor stdio
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+
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+Start passt for the destination side::
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+
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+ passt --vhost-user --socket ~/passt_dst.socket --repair-path ~/passt-repair_dst.socket
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+
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+Start passt-repair::
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+
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+ passt-repair ~/passt-repair_dst.socket
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+
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+Start QEMU with the ``-incoming`` parameter:
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+
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+.. parsed-literal::
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+ |qemu_system| [...OPTIONS...] [...VHOST USER OPTIONS...] -incoming tcp:localhost:4444
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+
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+Then in the source guest monitor the migration can be started::
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+
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+ (qemu) migrate tcp:localhost:4444
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+
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+A separate passt-repair instance must be started for every migration. In the case of a failed migration, passt-repair also needs to be restarted before trying
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+again.
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+
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Hubs
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Hubs
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~~~~
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~~~~
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Stefan Hajnoczi