Re: [PATCH v3 08/10] qmp: teach 'getfd' to import sockets on win32

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

On Tue, Feb 07, 2023 at 06:25:33PM +0400, marcandre.lureau@redhat.com wrote:
> From: Marc-André Lureau <marcandre.lureau@redhat.com>
> 
> A process with enough capabilities can duplicate a socket to QEMU.
> Modify 'getfd' to import it and add it to the monitor fd list, so it can
> be later used by other commands.
> 
> Note that we actually store the SOCKET in the FD list, appropriate care
> must now be taken to use the correct socket functions (similar approach
> is taken by our io/ code and in glib, this is internal and shouldn't
> affect the QEMU/QMP users)
> 
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
>  qapi/misc.json     | 16 ++++++++--
>  monitor/fds.c      | 79 ++++++++++++++++++++++++++++++++++++----------
>  monitor/hmp-cmds.c |  6 +++-
>  3 files changed, 81 insertions(+), 20 deletions(-)
> 
> diff --git a/qapi/misc.json b/qapi/misc.json
> index 27ef5a2b20..cd36d8befb 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -249,10 +249,18 @@
>  ##
>  # @getfd:
>  #
> -# Receive a file descriptor via SCM rights and assign it a name
> +# On UNIX, receive a file descriptor via SCM rights and assign it a name.
> +#
> +# On Windows, (where ancillary socket fd-passing isn't an option yet), add a
> +# socket that was duplicated to QEMU process with WSADuplicateSocketW() via
> +# WSASocket() & WSAPROTOCOL_INFOW structure and assign it a name. A SOCKET is
> +# considered as a kind of "file descriptor" in QMP context, for historical
> +# reasons and simplicity. QEMU takes care to use socket functions appropriately.
>  #
>  # @fdname: file descriptor name
>  #
> +# @wsa-info: a WSAPROTOCOL_INFOW structure (encoded in base64). Since 8.0.

This is a clever trick, but it also feels pretty gross from
POV of QMP design normal practice, which would be to define
a struct in QAPI to represent the WSAPROTOCOL_INFOW contents.

The main downside would be that its more verbose to convert
between the windows and QAPI structs.


> @@ -270,7 +278,11 @@
>  # <- { "return": {} }
>  #
>  ##
> -{ 'command': 'getfd', 'data': {'fdname': 'str'} }
> +{ 'command': 'getfd', 'data': {
> +    'fdname': 'str',
> +    '*wsa-info': {'type': 'str', 'if': 'CONFIG_WIN32'}
> +  }
> +}

snip

> +void qmp_getfd(const char *fdname,
> +#ifdef WIN32
> +               const char *wsa_info,
> +#endif
> +               Error **errp)
> +{
> +    Monitor *cur_mon = monitor_cur();
> +    int fd;
> +
> +#ifdef WIN32
> +    if (wsa_info) {
> +        g_autofree WSAPROTOCOL_INFOW *info = NULL;
> +        gsize len;
> +        SOCKET sk;
> +
> +        info = (void *)g_base64_decode(wsa_info, &len);
> +        if (len != sizeof(*info)) {
> +            error_setg(errp, "Invalid WSAPROTOCOL_INFOW value");
> +            return;
> +        }


With regards,
Daniel
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