Re: [PATCH V1 22/32] char: qio_channel_socket_accept reuse fd

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Juan Quintela" <quintela@redhat.com>,
	qemu-devel@nongnu.org, "Markus Armbruster" <armbru@redhat.com>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Steve Sistare" <steven.sistare@oracle.com>,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Alex Bennée" <alex.bennee@linaro.org>
Subject: Re: [PATCH V1 22/32] char: qio_channel_socket_accept reuse fd
Date: Tue, 15 Sep 2020 18:53:59 +0100	[thread overview]
Message-ID: <20200915175359.GM1502912@redhat.com> (raw)
In-Reply-To: <20200915173334.GD2922@work-vm>

On Tue, Sep 15, 2020 at 06:33:34PM +0100, Dr. David Alan Gilbert wrote:
> * Steve Sistare (steven.sistare@oracle.com) wrote:
> > From: Mark Kanda <mark.kanda@oracle.com>
> > 
> > Add an fd argument to qio_channel_socket_accept.  If not -1, the channel
> > uses that fd instead of accepting a new socket connection.  All callers
> > pass -1 in this patch, so no functional change.
> 
> Doesn't some of this just come from the fact you're insisting on reusing
> the command line?   We should be able to open a chardev on an fd
> shouldn't we?

Even ignoring that question, this patch looks pointless to me. The callers
have to be modified to pass in the FD to use instead of accepting a new
connection. Given that, you migt as well just modify the callers to use
the FD immediately if valid and never call qio_channel_socket_accept at all.

ie

   if (reuse_fd)
      fd = reuse_fd;
   else
      fd = qio_channel_socket_accept(ioc...)

> 
> Dave
> 
> > Signed-off-by: Mark Kanda <mark.kanda@oracle.com>
> > Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
> > ---
> >  include/io/channel-socket.h    |  3 ++-
> >  io/channel-socket.c            | 12 +++++++++---
> >  io/net-listener.c              |  4 ++--
> >  scsi/qemu-pr-helper.c          |  2 +-
> >  tests/qtest/tpm-emu.c          |  2 +-
> >  tests/test-char.c              |  2 +-
> >  tests/test-io-channel-socket.c |  4 ++--
> >  7 files changed, 18 insertions(+), 11 deletions(-)
> > 
> > diff --git a/include/io/channel-socket.h b/include/io/channel-socket.h
> > index 777ff59..0ffc560 100644
> > --- a/include/io/channel-socket.h
> > +++ b/include/io/channel-socket.h
> > @@ -248,6 +248,7 @@ qio_channel_socket_get_remote_address(QIOChannelSocket *ioc,
> >  /**
> >   * qio_channel_socket_accept:
> >   * @ioc: the socket channel object
> > + * @reuse_fd: fd to reuse; -1 otherwise
> >   * @errp: pointer to a NULL-initialized error object
> >   *
> >   * If the socket represents a server, then this accepts
> > @@ -258,7 +259,7 @@ qio_channel_socket_get_remote_address(QIOChannelSocket *ioc,
> >   */
> >  QIOChannelSocket *
> >  qio_channel_socket_accept(QIOChannelSocket *ioc,
> > -                          Error **errp);
> > +                          int reuse_fd, Error **errp);
> >  
> >  
> >  #endif /* QIO_CHANNEL_SOCKET_H */
> > diff --git a/io/channel-socket.c b/io/channel-socket.c
> > index e1b4667..dde12bf 100644
> > --- a/io/channel-socket.c
> > +++ b/io/channel-socket.c
> > @@ -352,7 +352,7 @@ void qio_channel_socket_dgram_async(QIOChannelSocket *ioc,
> >  
> >  QIOChannelSocket *
> >  qio_channel_socket_accept(QIOChannelSocket *ioc,
> > -                          Error **errp)
> > +                          int reuse_fd, Error **errp)
> >  {
> >      QIOChannelSocket *cioc;
> >  
> > @@ -362,8 +362,14 @@ qio_channel_socket_accept(QIOChannelSocket *ioc,
> >  
> >   retry:
> >      trace_qio_channel_socket_accept(ioc);
> > -    cioc->fd = qemu_accept(ioc->fd, (struct sockaddr *)&cioc->remoteAddr,
> > -                           &cioc->remoteAddrLen);
> > +
> > +    if (reuse_fd != -1) {
> > +        cioc->fd = reuse_fd;
> > +    } else {
> > +        cioc->fd = qemu_accept(ioc->fd, (struct sockaddr *)&cioc->remoteAddr,
> > +                               &cioc->remoteAddrLen);
> > +    }
> > +
> >      if (cioc->fd < 0) {
> >          if (errno == EINTR) {
> >              goto retry;
> > diff --git a/io/net-listener.c b/io/net-listener.c
> > index 5d8a226..bbdea1e 100644
> > --- a/io/net-listener.c
> > +++ b/io/net-listener.c
> > @@ -45,7 +45,7 @@ static gboolean qio_net_listener_channel_func(QIOChannel *ioc,
> >      QIOChannelSocket *sioc;
> >  
> >      sioc = qio_channel_socket_accept(QIO_CHANNEL_SOCKET(ioc),
> > -                                     NULL);
> > +                                     -1, NULL);
> >      if (!sioc) {
> >          return TRUE;
> >      }
> > @@ -194,7 +194,7 @@ static gboolean qio_net_listener_wait_client_func(QIOChannel *ioc,
> >      QIOChannelSocket *sioc;
> >  
> >      sioc = qio_channel_socket_accept(QIO_CHANNEL_SOCKET(ioc),
> > -                                     NULL);
> > +                                     -1, NULL);
> >      if (!sioc) {
> >          return TRUE;
> >      }
> > diff --git a/scsi/qemu-pr-helper.c b/scsi/qemu-pr-helper.c
> > index 57ad830..0e6d683 100644
> > --- a/scsi/qemu-pr-helper.c
> > +++ b/scsi/qemu-pr-helper.c
> > @@ -800,7 +800,7 @@ static gboolean accept_client(QIOChannel *ioc, GIOCondition cond, gpointer opaqu
> >      PRHelperClient *prh;
> >  
> >      cioc = qio_channel_socket_accept(QIO_CHANNEL_SOCKET(ioc),
> > -                                     NULL);
> > +                                     -1, NULL);
> >      if (!cioc) {
> >          return TRUE;
> >      }
> > diff --git a/tests/qtest/tpm-emu.c b/tests/qtest/tpm-emu.c
> > index 2e8eb7b..19e5dab 100644
> > --- a/tests/qtest/tpm-emu.c
> > +++ b/tests/qtest/tpm-emu.c
> > @@ -83,7 +83,7 @@ void *tpm_emu_ctrl_thread(void *data)
> >      g_cond_signal(&s->data_cond);
> >  
> >      qio_channel_wait(QIO_CHANNEL(lioc), G_IO_IN);
> > -    ioc = QIO_CHANNEL(qio_channel_socket_accept(lioc, &error_abort));
> > +    ioc = QIO_CHANNEL(qio_channel_socket_accept(lioc, -1, &error_abort));
> >      g_assert(ioc);
> >  
> >      {
> > diff --git a/tests/test-char.c b/tests/test-char.c
> > index 614bdac..1bb6ae0 100644
> > --- a/tests/test-char.c
> > +++ b/tests/test-char.c
> > @@ -884,7 +884,7 @@ char_socket_client_server_thread(gpointer data)
> >      QIOChannelSocket *cioc;
> >  
> >  retry:
> > -    cioc = qio_channel_socket_accept(ioc, &error_abort);
> > +    cioc = qio_channel_socket_accept(ioc, -1, &error_abort);
> >      g_assert_nonnull(cioc);
> >  
> >      if (char_socket_ping_pong(QIO_CHANNEL(cioc), NULL) != 0) {
> > diff --git a/tests/test-io-channel-socket.c b/tests/test-io-channel-socket.c
> > index d43083a..0d410cf 100644
> > --- a/tests/test-io-channel-socket.c
> > +++ b/tests/test-io-channel-socket.c
> > @@ -75,7 +75,7 @@ static void test_io_channel_setup_sync(SocketAddress *listen_addr,
> >      qio_channel_set_delay(*src, false);
> >  
> >      qio_channel_wait(QIO_CHANNEL(lioc), G_IO_IN);
> > -    *dst = QIO_CHANNEL(qio_channel_socket_accept(lioc, &error_abort));
> > +    *dst = QIO_CHANNEL(qio_channel_socket_accept(lioc, -1, &error_abort));
> >      g_assert(*dst);
> >  
> >      test_io_channel_set_socket_bufs(*src, *dst);
> > @@ -143,7 +143,7 @@ static void test_io_channel_setup_async(SocketAddress *listen_addr,
> >      g_assert(!data.err);
> >  
> >      qio_channel_wait(QIO_CHANNEL(lioc), G_IO_IN);
> > -    *dst = QIO_CHANNEL(qio_channel_socket_accept(lioc, &error_abort));
> > +    *dst = QIO_CHANNEL(qio_channel_socket_accept(lioc, -1, &error_abort));
> >      g_assert(*dst);
> >  
> >      qio_channel_set_delay(*src, false);
> > -- 
> > 1.8.3.1
> > 
> -- 
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Regards,
Daniel
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