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

[Markus Armbruster <armbru@redhat.com>]

Marc-André Lureau <marcandre.lureau@gmail.com> writes:

> Hi
>
> On Mon, Feb 20, 2023 at 12:26 PM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Marc-André Lureau <marcandre.lureau@gmail.com> writes:
>>
>> > Hi Markus
>> >
>> > On Fri, Feb 17, 2023 at 1:49 PM Markus Armbruster <armbru@redhat.com> wrote:
>> >>
>> >> marcandre.lureau@redhat.com writes:
>> >>
>> >> > 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.
>> >>
>> >> The Windows part explains things in terms of the C socket API.  Less
>> >> than ideal for the QEMU QMP Reference Manual, isn't it?  I don't know
>> >> nearly enough about this stuff to suggest concrete improvements...
>> >
>> > We don't have to, after all we don't explain how to use sendmsg/cmsg
>> > stuff to pass FDs.
>> >
>> > I will drop the part about "A SOCKET is considered as a kind of "file
>> > descriptor" in QMP context", after we get "[PATCH 0/4] win32: do not
>> > mix SOCKET and fd space"
>> > (https://patchew.org/QEMU/20230212204942.1905959-1-marcandre.lureau@redhat.com/)
>> > merged.
>>
>> Would it make sense to rebase this series on top of that one, so we
>> can have simpler documentation from the start?
>
> Sure, if only I had more reviews/acks...

I'll try to have a look.

>> >> What does this command do under Windows before this patch?  Fail always?
>> >
>> > Without ancillary data support on Windows, you can't make it work.
>>
>> Yes, but how does it fail?  Hmm, you actually answer that below.

[...]

>> >> >  # Returns: Nothing on success
>> >> >  #
>> >> >  # Since: 0.14
>> >> > @@ -270,7 +278,11 @@
>> >> >  # <- { "return": {} }
>> >> >  #
>> >> >  ##
>> >> > -{ 'command': 'getfd', 'data': {'fdname': 'str'} }
>> >> > +{ 'command': 'getfd', 'data': {
>> >> > +    'fdname': 'str',
>> >> > +    '*wsa-info': {'type': 'str', 'if': 'CONFIG_WIN32'}
>> >> > +  }
>> >> > +}
>> >>
>> >> What happens when QEMU runs on a Windows host and the client doesn't
>> >> pass @wsa-info?
>> >
>> > It attempts to get the fd from the last recv, but it will fail on
>> > Windows, this is not available.
>>
>> So it fails exactly like it fails on a POSIX host when you execute getfd
>> without passing along a file descriptor with SCM_RIGHTS.  Correct?
>
> Correct, I get something like:
> Error { class: GenericError, desc: "No file descriptor supplied via
> SCM_RIGHTS", id: None }

Works for me, thanks!