| Message ID | 20250311132714.166189-1-lvivier@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] docs: Explain how to use passt | expand |
On Tue, Mar 11, 2025 at 02:27:14PM +0100, Laurent Vivier wrote: > Add a chapter to explain how to use passt(1) instead of '-net user'. > passt(1) can be connected to QEMU using UNIX socket or vhost-user. > With vhost-user, migration of the VM is allowed and internal state of > passt(1) is transfered from one side to the other > > Bug: https://gitlab.com/qemu-project/qemu/-/issues/2827 > Signed-off-by: Laurent Vivier <lvivier@redhat.com> Reviewed-by: David Gibson <david@gibson.dropbear.id.au> > --- > docs/system/devices/net.rst | 100 ++++++++++++++++++++++++++++++++++++ > 1 file changed, 100 insertions(+) > > diff --git a/docs/system/devices/net.rst b/docs/system/devices/net.rst > index 2ab516d4b097..a3efbdcabd1a 100644 > --- a/docs/system/devices/net.rst > +++ b/docs/system/devices/net.rst > @@ -77,6 +77,106 @@ When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP > connections can be redirected from the host to the guest. It allows for > example to redirect X11, telnet or SSH connections. > > +Using passt as the user mode network stack > +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > + > +passt_ can be used as a simple replacement for SLIRP (``-net user``). > +passt doesn't require any capability or privilege. passt has > +better performance than ``-net user``, full IPv6 support and better security > +as it's a daemon that is not executed in QEMU context. > + > +passt can be connected to QEMU either by using a socket > +(``-netdev stream``) or using the vhost-user interface (``-netdev vhost-user``). > +See `passt(1)`_ for more details on passt. > + > +.. _passt: https://passt.top/ > +.. _passt(1): https://passt.top/builds/latest/web/passt.1.html > + > +To use socket based passt interface: > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > + > +Start passt as a daemon:: > + > + passt --socket ~/passt.socket > + > +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``, > +...). Then you can connect your QEMU instance to passt: > + > +.. parsed-literal:: > + |qemu_system| [...OPTIONS...] -device virtio-net-pci,netdev=netdev0 -netdev stream,id=netdev0,server=off,addr.type=unix,addr.path=~/passt.socket > + > +Where ``~/passt.socket`` is the UNIX socket created by passt to > +communicate with QEMU. > + > +To use vhost-based interface: > +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > + > +Start passt with ``--vhost-user``:: > + > + passt --vhost-user --socket ~/passt.socket > + > +Then to connect QEMU: > + > +.. parsed-literal:: > + |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 > + > +Where ``$RAMSIZE`` is the memory size of your VM ``-m`` and ``-object memory-backend-memfd,size=`` must match. > + > +Migration of passt: > +^^^^^^^^^^^^^^^^^^^ > + > +When passt is connected to QEMU using the vhost-user interface it can > +be migrated with QEMU and the network connections are not interrupted. > + > +As passt runs with no privileges, it relies on passt-repair to save and > +load the TCP connections state, using the TCP_REPAIR socket option. > +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. > + > +Example of migration of a guest on the same host > +________________________________________________ > + > +Before being able to run passt-repair, the CAP_NET_ADMIN capability must be set > +on the file, run as root:: > + > + setcap cap_net_admin+eip ./passt-repair > + > +Start passt for the source side:: > + > + passt --vhost-user --socket ~/passt_src.socket --repair-path ~/passt-repair_src.socket > + > +Where ``~/passt-repair_src.socket`` is the UNIX socket created by passt to > +communicate with passt-repair. The default value is the ``--socket`` path > +appended with ``.repair``. > + > +Start passt-repair:: > + > + passt-repair ~/passt-repair_src.socket > + > +Start source side QEMU with a monitor to be able to send the migrate command: > + > +.. parsed-literal:: > + |qemu_system| [...OPTIONS...] [...VHOST USER OPTIONS...] -monitor stdio > + > +Start passt for the destination side:: > + > + passt --vhost-user --socket ~/passt_dst.socket --repair-path ~/passt-repair_dst.socket > + > +Start passt-repair:: > + > + passt-repair ~/passt-repair_dst.socket > + > +Start QEMU with the ``-incoming`` parameter: > + > +.. parsed-literal:: > + |qemu_system| [...OPTIONS...] [...VHOST USER OPTIONS...] -incoming tcp:localhost:4444 > + > +Then in the source guest monitor the migration can be started:: > + > + (qemu) migrate tcp:localhost:4444 > + > +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 > +again. > + > Hubs > ~~~~ >
diff --git a/docs/system/devices/net.rst b/docs/system/devices/net.rst index 2ab516d4b097..a3efbdcabd1a 100644 --- a/docs/system/devices/net.rst +++ b/docs/system/devices/net.rst @@ -77,6 +77,106 @@ When using the ``'-netdev user,hostfwd=...'`` option, TCP or UDP connections can be redirected from the host to the guest. It allows for example to redirect X11, telnet or SSH connections. +Using passt as the user mode network stack +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +passt_ can be used as a simple replacement for SLIRP (``-net user``). +passt doesn't require any capability or privilege. passt has +better performance than ``-net user``, full IPv6 support and better security +as it's a daemon that is not executed in QEMU context. + +passt can be connected to QEMU either by using a socket +(``-netdev stream``) or using the vhost-user interface (``-netdev vhost-user``). +See `passt(1)`_ for more details on passt. + +.. _passt: https://passt.top/ +.. _passt(1): https://passt.top/builds/latest/web/passt.1.html + +To use socket based passt interface: +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Start passt as a daemon:: + + passt --socket ~/passt.socket + +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``, +...). Then you can connect your QEMU instance to passt: + +.. parsed-literal:: + |qemu_system| [...OPTIONS...] -device virtio-net-pci,netdev=netdev0 -netdev stream,id=netdev0,server=off,addr.type=unix,addr.path=~/passt.socket + +Where ``~/passt.socket`` is the UNIX socket created by passt to +communicate with QEMU. + +To use vhost-based interface: +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Start passt with ``--vhost-user``:: + + passt --vhost-user --socket ~/passt.socket + +Then to connect QEMU: + +.. parsed-literal:: + |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 + +Where ``$RAMSIZE`` is the memory size of your VM ``-m`` and ``-object memory-backend-memfd,size=`` must match. + +Migration of passt: +^^^^^^^^^^^^^^^^^^^ + +When passt is connected to QEMU using the vhost-user interface it can +be migrated with QEMU and the network connections are not interrupted. + +As passt runs with no privileges, it relies on passt-repair to save and +load the TCP connections state, using the TCP_REPAIR socket option. +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. + +Example of migration of a guest on the same host +________________________________________________ + +Before being able to run passt-repair, the CAP_NET_ADMIN capability must be set +on the file, run as root:: + + setcap cap_net_admin+eip ./passt-repair + +Start passt for the source side:: + + passt --vhost-user --socket ~/passt_src.socket --repair-path ~/passt-repair_src.socket + +Where ``~/passt-repair_src.socket`` is the UNIX socket created by passt to +communicate with passt-repair. The default value is the ``--socket`` path +appended with ``.repair``. + +Start passt-repair:: + + passt-repair ~/passt-repair_src.socket + +Start source side QEMU with a monitor to be able to send the migrate command: + +.. parsed-literal:: + |qemu_system| [...OPTIONS...] [...VHOST USER OPTIONS...] -monitor stdio + +Start passt for the destination side:: + + passt --vhost-user --socket ~/passt_dst.socket --repair-path ~/passt-repair_dst.socket + +Start passt-repair:: + + passt-repair ~/passt-repair_dst.socket + +Start QEMU with the ``-incoming`` parameter: + +.. parsed-literal:: + |qemu_system| [...OPTIONS...] [...VHOST USER OPTIONS...] -incoming tcp:localhost:4444 + +Then in the source guest monitor the migration can be started:: + + (qemu) migrate tcp:localhost:4444 + +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 +again. + Hubs ~~~~
Add a chapter to explain how to use passt(1) instead of '-net user'. passt(1) can be connected to QEMU using UNIX socket or vhost-user. With vhost-user, migration of the VM is allowed and internal state of passt(1) is transfered from one side to the other Bug: https://gitlab.com/qemu-project/qemu/-/issues/2827 Signed-off-by: Laurent Vivier <lvivier@redhat.com> --- docs/system/devices/net.rst | 100 ++++++++++++++++++++++++++++++++++++ 1 file changed, 100 insertions(+)