Re: [libvirt PATCH 0/3] Support for restarting passt backend

["Michal Prívozník" <mprivozn@redhat.com>]

On 2/22/23 01:35, Laine Stump wrote:
> If the passt process that implements the backend of a QEMU emulated
> network device terminates, QEMU itself is incapable of restarting a
> new process so that the networking can begin... working again.
> 
> However, what QEMU can and does do is:
> 
> 1) send the NETDEV_STREAM_DISCONNECTED event to libvirt when it sees
>    that the socket has been closed (this event has been in QEMU for as
>    long as support for "-netdev stream", which is used for connecting
>    to passt)
> 
> 2) as of QEMU 8.0.0, the qemu commandline for -netdev stream accepts
>    the "reconnect" option, which tells QEMU to attempt reconnecting to
>    the same socket it previously used, repeating the attempt every "n"
>    seconds (the only argument to reconnect) until it is successful.
> 
> If libvirt adds the reconnect option to the qemu commandline, and then
> responds to a NETDEV_STREAM_DISCONNECTED event by re-running the same
> passt command that it ran when the device was originally connected,
> then a guest will be able to recover in the (very unlikely, according
> to Stefano!) event that the original passt process unexpectedly exits,
> or is killed by some external entity.
> 
> Patch 2/3 handles (2) above, while patch 3/3 handles (1). (patch 1/3
> is a short guest appearance by pkrempa. Thanks pkrempa!).
> 
> This resolves https://bugzilla.redhat.com/2172098
> 
> Along with Stefano's series fixing up selinux issues related to
> running the passt process, they make the passt backend very usable.
> 
> Laine Stump (2):
>   qemu: add reconnect=5 to passt qemu commandline options when available
>   qemu: respond to NETDEV_STREAM_DISCONNECTED event
> 
> Peter Krempa (1):
>   qemu: capabilities: Introduce QEMU_CAPS_NETDEV_STREAM_RECONNECT
> 
>  src/qemu/qemu_capabilities.c                  |  4 +
>  src/qemu/qemu_capabilities.h                  |  3 +
>  src/qemu/qemu_domain.c                        |  1 +
>  src/qemu/qemu_domain.h                        |  1 +
>  src/qemu/qemu_driver.c                        | 82 +++++++++++++++++++
>  src/qemu/qemu_monitor.c                       | 11 +++
>  src/qemu/qemu_monitor.h                       |  6 ++
>  src/qemu/qemu_monitor_json.c                  | 16 ++++
>  src/qemu/qemu_passt.c                         | 11 +++
>  src/qemu/qemu_process.c                       | 18 ++++
>  .../caps_8.0.0.x86_64.xml                     |  1 +
>  .../net-user-passt.x86_64-7.2.0.args          | 37 +++++++++
>  .../net-user-passt.x86_64-latest.args         |  2 +-
>  tests/qemuxml2argvtest.c                      |  1 +
>  14 files changed, 193 insertions(+), 1 deletion(-)
>  create mode 100644 tests/qemuxml2argvdata/net-user-passt.x86_64-7.2.0.args
> 

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>

Michal