Re: [PATCH v3 5/5] utils/qemu-sockets: Introduce inet socket options controlling TCP keep-alive

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

On Tue, Apr 08, 2025 at 01:25:04PM +0200, Juraj Marcin wrote:
> From: Juraj Marcin <jmarcin@redhat.com>
> 
> With the default TCP stack configuration, it could be even 2 hours
> before the connection times out due to the other side not being
> reachable. However, in some cases, the application needs to be aware of
> a connection issue much sooner.
> 
> This is the case, for example, for postcopy live migration. If there is
> no traffic from the migration destination guest (server-side) to the
> migration source guest (client-side), the destination keeps waiting for
> pages indefinitely and does not switch to the postcopy-paused state.
> This can happen, for example, if the destination QEMU instance is
> started with the '-S' command line option and the machine is not started
> yet, or if the machine is idle and produces no new page faults for
> not-yet-migrated pages.
> 
> This patch introduces new inet socket parameters that control count,
> idle period, and interval of TCP keep-alive packets before the
> connection is considered broken. These parameters are available on
> systems where the respective TCP socket options are defined
> (TCP_KEEPCNT, TCP_KEEPIDLE, TCP_KEEPINTVL).
> 
> The default value for all is 0, which means the system configuration is
> used.
> 
> Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
> ---
>  meson.build         |  6 ++++
>  qapi/sockets.json   | 15 ++++++++
>  util/qemu-sockets.c | 88 +++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 109 insertions(+)
> 
> diff --git a/meson.build b/meson.build
> index 41f68d3806..680f47cf42 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2734,6 +2734,12 @@ if linux_io_uring.found()
>    config_host_data.set('HAVE_IO_URING_PREP_WRITEV2',
>                         cc.has_header_symbol('liburing.h', 'io_uring_prep_writev2'))
>  endif
> +config_host_data.set('HAVE_TCP_KEEPCNT',
> +                     cc.has_header_symbol('netinet/tcp.h', 'TCP_KEEPCN'T))
> +config_host_data.set('HAVE_TCP_KEEPIDLE',
> +                     cc.has_header_symbol('netinet/tcp.h', 'TCP_KEEPIDLE'))
> +config_host_data.set('HAVE_TCP_KEEPINTVL',
> +                     cc.has_header_symbol('netinet/tcp.h', 'TCP_KEEPINTVL'))

What platforms are you aware of that do NOT have these
settings available ? I'm wondering if we can just assume
they always exist.

>  
>  # has_member
>  config_host_data.set('HAVE_SIGEV_NOTIFY_THREAD_ID',
> diff --git a/qapi/sockets.json b/qapi/sockets.json
> index 62797cd027..bb9d298635 100644
> --- a/qapi/sockets.json
> +++ b/qapi/sockets.json
> @@ -59,6 +59,18 @@
>  # @keep-alive: enable keep-alive when connecting to/listening on this socket.
>  #     (Since 4.2, not supported for listening sockets until 10.1)
>  #
> +# @keep-alive-count: number of keep-alive packets sent before the connection is
> +#     closed.  Only supported for TCP sockets on systems where TCP_KEEPCNT
> +#     socket option is defined.  (Since 10.1)
> +#
> +# @keep-alive-idle: time in seconds the connection needs to be idle before
> +#     sending a keepalive packet.  Only supported for TCP sockets on systems
> +#     where TCP_KEEPIDLE socket option is defined.  (Since 10.1)
> +#
> +# @keep-alive-interval: time in secods between keep-alive packets.  Only

Trivial typo s/secods/seconds/

> +#     supported for TCP sockets on systems where TCP_KEEPINTVL is defined.
> +#     (Since 10.1)
> +#
>  # @mptcp: enable multi-path TCP.  (Since 6.1)
>  #
>  # Since: 1.3
> @@ -71,6 +83,9 @@
>      '*ipv4': 'bool',
>      '*ipv6': 'bool',
>      '*keep-alive': 'bool',
> +    '*keep-alive-count': { 'type': 'uint32', 'if': 'HAVE_TCP_KEEPCNT' },
> +    '*keep-alive-idle': { 'type': 'uint32', 'if': 'HAVE_TCP_KEEPIDLE' },
> +    '*keep-alive-interval': { 'type': 'uint32', 'if': 'HAVE_TCP_KEEPINTVL' },
>      '*mptcp': { 'type': 'bool', 'if': 'HAVE_IPPROTO_MPTCP' } } }
>  
>  ##

With regards,
Daniel
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