Re: [PATCH v6 05/13] qapi: net: add stream and dgram netdevs

[Markus Armbruster <armbru@redhat.com>]

Laurent Vivier <lvivier@redhat.com> writes:

> Copied from socket netdev file and modified to use SocketAddress
> to be able to introduce new features like unix socket.
>
> "udp" and "mcast" are squashed into dgram netdev, multicast is detected
> according to the IP address type.
> "listen" and "connect" modes are managed by stream netdev. An optional
> parameter "server" defines the mode (server by default)
>
> The two new types need to be parsed the modern way with -netdev, because
> with the traditional way, the "type" field of netdev structure collides with
> the "type" field of SocketAddress and prevents the correct evaluation of the
> command line option. Moreover the traditional way doesn't allow to use
> the same type (SocketAddress) several times with the -netdev option
> (needed to specify "local" and "remote" addresses).
>
> The previous commit paved the way for parsing the modern way, but
> omitted one detail: how to pick modern vs. traditional, in
> netdev_is_modern().
>
> We want to pick based on the value of parameter "type".  But how to
> extract it from the option argument?
>
> Parsing the option argument, either the modern or the traditional way,
> extracts it for us, but only if parsing succeeds.
>
> If parsing fails, there is no good option.  No matter which parser we
> pick, it'll be the wrong one for some arguments, and the error
> reporting will be confusing.
>
> Fortunately, the traditional parser accepts *anything* when called in
> a certain way.  This maximizes our chance to extract the value of
> "type", and in turn minimizes the risk of confusing error reporting.
>
> Signed-off-by: Laurent Vivier <lvivier@redhat.com>
> Reviewed-by: Stefano Brivio <sbrivio@redhat.com>

[...]

> diff --git a/qapi/net.json b/qapi/net.json
> index 9af11e9a3bb2..4c5245321947 100644
> --- a/qapi/net.json
> +++ b/qapi/net.json
> @@ -7,6 +7,7 @@
>  ##
>  
>  { 'include': 'common.json' }
> +{ 'include': 'sockets.json' }
>  
>  ##
>  # @set_link:
> @@ -566,6 +567,57 @@
>      '*isolated':  'bool' },
>    'if': 'CONFIG_VMNET' }
>  
> +##
> +# @NetdevStreamOptions:
> +#
> +# Configuration info for stream socket netdev
> +#
> +# @addr: socket address to listen on (server=true)
> +#        or connect to (server=false)
> +# @server: create server socket (default: true)
> +#
> +# Only SocketAddress types 'inet' and 'fd' are supported.
> +#
> +# Since: 7.1
> +##
> +{ 'struct': 'NetdevStreamOptions',
> +  'data': {
> +    'addr':   'SocketAddress',
> +    '*server': 'bool' } }
> +
> +##
> +# @NetdevDgramOptions:
> +#
> +# Configuration info for datagram socket netdev.
> +#
> +# @remote: remote address
> +# @local: local address
> +#
> +# Only SocketAddress types 'inet' and 'fd' are supported.
> +#
> +# The code checks there is at least one of these options and reports an error
> +# if not. If remote address is present and it's a multicast address, local
> +# address is optional. Otherwise local address is required and remote address
> +# is optional.
> +#
> +# Valid parameters combination table:
> +#
> +#    @remote         @local      |   okay?
> +#    ----------------------------+--------
> +#    absent          absent      |   no
> +#    absent          present     |   yes
> +#    multicast       absent      |   yes
> +#    multicast       present     |   yes
> +#    not multicast   absent      |   no
> +#    not multicast   present     |   yes

You need to use suitable markup for the table.  As is, it comes out like

    remote local | okay? —————————-+——– absent absent | no absent present | yes multicast absent | yes multicast present | yes not multicast absent | no not multicast present | yes

in formatted documentation.

Possibly useful: https://pandemic-overview.readthedocs.io/en/latest/myGuides/reStructuredText-Tables-Examples.html

I created this table in my review of v4 to double-check I got the doc
text.  Keep it only if *you* think it's useful.  Feel free to delete it.

> +#
> +# Since: 7.1
> +##
> +{ 'struct': 'NetdevDgramOptions',
> +  'data': {
> +    '*local':  'SocketAddress',
> +    '*remote': 'SocketAddress' } }
> +
>  ##
>  # @NetClientDriver:
>  #
> @@ -579,8 +631,9 @@
>  #        @vmnet-bridged since 7.1
>  ##
>  { 'enum': 'NetClientDriver',
> -  'data': [ 'none', 'nic', 'user', 'tap', 'l2tpv3', 'socket', 'vde',
> -            'bridge', 'hubport', 'netmap', 'vhost-user', 'vhost-vdpa',
> +  'data': [ 'none', 'nic', 'user', 'tap', 'l2tpv3', 'socket', 'stream',
> +            'dgram', 'vde', 'bridge', 'hubport', 'netmap', 'vhost-user',
> +            'vhost-vdpa',
>              { 'name': 'vmnet-host', 'if': 'CONFIG_VMNET' },
>              { 'name': 'vmnet-shared', 'if': 'CONFIG_VMNET' },
>              { 'name': 'vmnet-bridged', 'if': 'CONFIG_VMNET' }] }
> @@ -610,6 +663,8 @@
>      'tap':      'NetdevTapOptions',
>      'l2tpv3':   'NetdevL2TPv3Options',
>      'socket':   'NetdevSocketOptions',
> +    'stream':   'NetdevStreamOptions',
> +    'dgram':    'NetdevDgramOptions',
>      'vde':      'NetdevVdeOptions',
>      'bridge':   'NetdevBridgeOptions',
>      'hubport':  'NetdevHubPortOptions',
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 377d22fbd82f..215a2615f13f 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -2722,6 +2722,18 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>      "-netdev socket,id=str[,fd=h][,udp=host:port][,localaddr=host:port]\n"
>      "                configure a network backend to connect to another network\n"
>      "                using an UDP tunnel\n"
> +    "-netdev stream,id=str[,server=on|off],addr.type=inet,addr.host=host,addr.port=port\n"
> +    "-netdev stream,id=str[,server=on|off],addr.type=fd,addr.str=h\n"
> +    "                configure a network backend to connect to another network\n"
> +    "                using a socket connection in stream mode.\n"

This part needs to match NetdevStreamOptions above.

Missing here: the optional members of InetSocketAddress: numeric, to,
ipv4, ...  Do we care?

The next part needs to match NetdevDgramOptions above.

> +    "-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=inet,local.host=addr]\n"
> +    "-netdev dgram,id=str,remote.type=inet,remote.host=maddr,remote.port=port[,local.type=fd,local.str=h]\n"
> +    "                configure a network backend to connect to a multicast maddr and port\n"
> +    "                use ``local.host=addr`` to specify the host address to send packets from\n"

I figure this covers table rows

   #    @remote         @local      |   okay?
   #    ----------------------------+--------
   #    multicast       absent      |   yes
   #    multicast       present     |   yes

for remote.type=inet and any local.type.

What about remote.type=fd?

> +    "-netdev dgram,id=str,local.type=inet,local.host=addr,local.port=port[,remote.type=inet,remote.host=addr,remote.port=port]\n"

I figure this covers table rows

    #    absent          present     |   yes
    #    not multicast   present     |   yes

for *.type=inet.

> +    "-netdev dgram,id=str,local.type=fd,local.str=h\n"
> +    "                configure a network backend to connect to another network\n"
> +    "                using an UDP tunnel\n"

I figure this covers table row

   #    absent          present     |   yes

for local.type=fd.

Together, they cover table row

    #    absent          present     |   yes

for any local.type.  Good.

Table row

    #    not multicast   present     |   yes

is only covered for *.type=inet.  Could either of the types be fd?

>  #ifdef CONFIG_VDE
>      "-netdev vde,id=str[,sock=socketpath][,port=n][,group=groupname][,mode=octalmode]\n"
>      "                configure a network backend to connect to port 'n' of a vde switch\n"