Re: [Qemu-devel] [PATCH v4] qemu-char: don't issue CHR_EVENT_OPEN in a BH

[mdroth]

On Fri, Jun 07, 2013 at 09:50:39AM -0400, Luiz Capitulino wrote:
> On Tue,  4 Jun 2013 16:35:09 -0500
> Michael Roth <address@hidden> wrote:
> 
> > When CHR_EVENT_OPENED was initially added, it was CHR_EVENT_RESET,
> > and it was issued as a bottom-half:
> > 
> > 86e94dea5b740dad65446c857f6959eae43e0ba6
> > 
> > Which we basically used to print out a greeting/prompt for the
> > monitor.
> > 
> > AFAICT the only reason this was ever done in a BH was because in
> > some cases we'd modify the chr_write handler for a new chardev
> > backend *after* the site where we issued the reset (see:
> > 86e94d:qemu_chr_open_stdio())
> > 
> > At some point this event was renamed to CHR_EVENT_OPENED, and we've
> > maintained the use of this BH ever since.
> > 
> > However, due to 9f939df955a4152aad69a19a77e0898631bb2c18, we schedule
> > the BH via g_idle_add(), which is causing events to sometimes be
> > delivered after we've already begun processing data from backends,
> > leading to:
> > 
> >  known bugs:
> > 
> >   QMP:
> >     session negotation resets with OPENED event, in some cases this
> >     is causing new sessions to get sporadically reset
> > 
> >  potential bugs:
> > 
> >   hw/usb/redirect.c:
> >     can_read handler checks for dev->parser != NULL, which may be
> >     true if CLOSED BH has not been executed yet. In the past, OPENED
> >     quiesced outstanding CLOSED events prior to us reading client
> >     data. If it's delayed, our check may allow reads to occur even
> >     though we haven't processed the OPENED event yet, and when we
> >     do finally get the OPENED event, our state may get reset.
> > 
> >   qtest.c:
> >     can begin session before OPENED event is processed, leading to
> >     a spurious reset of the system and irq_levels
> > 
> >   gdbstub.c:
> >     may start a gdb session prior to the machine being paused
> > 
> > To fix these, let's just drop the BH.
> > 
> > Since the initial reasoning for using it still applies to an extent,
> > work around that by deferring the delivery of CHR_EVENT_OPENED until
> > after the chardevs have been fully initialized, toward the end of
> > qmp_chardev_add() (or some cases, qemu_chr_new_from_opts()). This
> > defers delivery long enough that we can be assured a CharDriverState
> > is fully initialized before CHR_EVENT_OPENED is sent.
> > 
> > Also, rather than requiring each chardev to do an explicit open, do it
> > automatically, and allow the small few who don't desire such behavior to
> > suppress the OPENED-on-init behavior by setting a 'explicit_be_open'
> > flag.
> > 
> > We additionally add missing OPENED events for stdio backends on w32,
> > which were previously not being issued, causing us to not recieve the
> > banner and initial prompts for qmp/hmp.
> > 
> > Reported-by: Stefan Priebe <address@hidden>
> > Cc: address@hidden
> > Signed-off-by: Michael Roth <address@hidden>
> 
> I don't know if the QMP queue is the ideal queue for this patch, but
> I'd happily apply it if I get at least one Reviewed-by from the CC'ed
> people.

Anthony actually added his Reviewed-by for v3, but I forgot to roll it
in the commit. If you do take it in through your tree can you add that?

Thanks!

> 
> 
> > ---
> > v3->v4:
> >  * renamed 'suppress_be_open_on_init' to 'explicit_be_open' to match
> >    existing 'explicit_fe_open' flag (Hans)
> >  * added missing 'explicit_be_open' flags for spice vmc/port and
> >    msmouse backends
> > 
> > v2->v3:
> >  * removed artifact in from v1 in backends/baum.c, test build with
> >    BRLAPI=y (Anthony)
> >  * rebased on latest origin/master
> > 
> > v1->v2:
> >  * default to sending OPENED on backend init, add flag to suppress
> >    it (Anthony)
> >  * fix missing OPENED for stdio backends on w32
> >  * fix missing OPENED when qemu_chr_new_from_opts() doesn't use
> >    qmp_chardev_add()
> >  * clean up/update commit message
> > 
> >  backends/baum.c       |    2 --
> >  backends/msmouse.c    |    1 +
> >  include/sysemu/char.h |    2 +-
> >  qemu-char.c           |   38 +++++++++++++++++---------------------
> >  spice-qemu-char.c     |    1 +
> >  ui/console.c          |    1 -
> >  ui/gtk.c              |    1 -
> >  7 files changed, 20 insertions(+), 26 deletions(-)
> > 
> > diff --git a/backends/baum.c b/backends/baum.c
> > index 4cba79f..62aa784 100644
> > --- a/backends/baum.c
> > +++ b/backends/baum.c
> > @@ -611,8 +611,6 @@ CharDriverState *chr_baum_init(void)
> >  
> >      qemu_set_fd_handler(baum->brlapi_fd, baum_chr_read, NULL, baum);
> >  
> > -    qemu_chr_be_generic_open(chr);
> > -
> >      return chr;
> >  
> >  fail:
> > diff --git a/backends/msmouse.c b/backends/msmouse.c
> > index 0ac05a0..c0dbfcd 100644
> > --- a/backends/msmouse.c
> > +++ b/backends/msmouse.c
> > @@ -70,6 +70,7 @@ CharDriverState *qemu_chr_open_msmouse(void)
> >      chr = g_malloc0(sizeof(CharDriverState));
> >      chr->chr_write = msmouse_chr_write;
> >      chr->chr_close = msmouse_chr_close;
> > +    chr->explicit_be_open = true;
> >  
> >      qemu_add_mouse_event_handler(msmouse_event, chr, 0, "QEMU Microsoft 
> > Mouse");
> >  
> > diff --git a/include/sysemu/char.h b/include/sysemu/char.h
> > index 5e42c90..066c216 100644
> > --- a/include/sysemu/char.h
> > +++ b/include/sysemu/char.h
> > @@ -70,12 +70,12 @@ struct CharDriverState {
> >      void (*chr_set_echo)(struct CharDriverState *chr, bool echo);
> >      void (*chr_set_fe_open)(struct CharDriverState *chr, int fe_open);
> >      void *opaque;
> > -    int idle_tag;
> >      char *label;
> >      char *filename;
> >      int be_open;
> >      int fe_open;
> >      int explicit_fe_open;
> > +    int explicit_be_open;
> >      int avail_connections;
> >      QemuOpts *opts;
> >      QTAILQ_ENTRY(CharDriverState) next;
> > diff --git a/qemu-char.c b/qemu-char.c
> > index d04b429..0b6ae95 100644
> > --- a/qemu-char.c
> > +++ b/qemu-char.c
> > @@ -110,19 +110,9 @@ void qemu_chr_be_event(CharDriverState *s, int event)
> >      s->chr_event(s->handler_opaque, event);
> >  }
> >  
> > -static gboolean qemu_chr_be_generic_open_bh(gpointer opaque)
> > -{
> > -    CharDriverState *s = opaque;
> > -    qemu_chr_be_event(s, CHR_EVENT_OPENED);
> > -    s->idle_tag = 0;
> > -    return FALSE;
> > -}
> > -
> >  void qemu_chr_be_generic_open(CharDriverState *s)
> >  {
> > -    if (s->idle_tag == 0) {
> > -        s->idle_tag = g_idle_add(qemu_chr_be_generic_open_bh, s);
> > -    }
> > +    qemu_chr_be_event(s, CHR_EVENT_OPENED);
> >  }
> >  
> >  int qemu_chr_fe_write(CharDriverState *s, const uint8_t *buf, int len)
> > @@ -247,6 +237,7 @@ static CharDriverState *qemu_chr_open_null(void)
> >  
> >      chr = g_malloc0(sizeof(CharDriverState));
> >      chr->chr_write = null_chr_write;
> > +    chr->explicit_be_open = true;
> >      return chr;
> >  }
> >  
> > @@ -504,9 +495,6 @@ static CharDriverState 
> > *qemu_chr_open_mux(CharDriverState *drv)
> >      /* Frontend guest-open / -close notification is not support with muxes 
> > */
> >      chr->chr_set_fe_open = NULL;
> >  
> > -    /* Muxes are always open on creation */
> > -    qemu_chr_be_generic_open(chr);
> > -
> >      return chr;
> >  }
> >  
> > @@ -883,8 +871,6 @@ static CharDriverState *qemu_chr_open_fd(int fd_in, int 
> > fd_out)
> >      chr->chr_update_read_handler = fd_chr_update_read_handler;
> >      chr->chr_close = fd_chr_close;
> >  
> > -    qemu_chr_be_generic_open(chr);
> > -
> >      return chr;
> >  }
> >  
> > @@ -1243,6 +1229,7 @@ static CharDriverState *qemu_chr_open_pty(const char 
> > *id,
> >      chr->chr_update_read_handler = pty_chr_update_read_handler;
> >      chr->chr_close = pty_chr_close;
> >      chr->chr_add_watch = pty_chr_add_watch;
> > +    chr->explicit_be_open = true;
> >  
> >      s->fd = io_channel_from_fd(master_fd);
> >      s->timer_tag = 0;
> > @@ -1595,8 +1582,6 @@ static CharDriverState *qemu_chr_open_pp_fd(int fd)
> >      chr->chr_close = pp_close;
> >      chr->opaque = drv;
> >  
> > -    qemu_chr_be_generic_open(chr);
> > -
> >      return chr;
> >  }
> >  #endif /* __linux__ */
> > @@ -1650,6 +1635,7 @@ static CharDriverState *qemu_chr_open_pp_fd(int fd)
> >      chr->opaque = (void *)(intptr_t)fd;
> >      chr->chr_write = null_chr_write;
> >      chr->chr_ioctl = pp_ioctl;
> > +    chr->explicit_be_open = true;
> >      return chr;
> >  }
> >  #endif
> > @@ -1880,7 +1866,6 @@ static CharDriverState *qemu_chr_open_win_path(const 
> > char *filename)
> >          g_free(chr);
> >          return NULL;
> >      }
> > -    qemu_chr_be_generic_open(chr);
> >      return chr;
> >  }
> >  
> > @@ -1980,7 +1965,6 @@ static CharDriverState 
> > *qemu_chr_open_pipe(ChardevHostdev *opts)
> >          g_free(chr);
> >          return NULL;
> >      }
> > -    qemu_chr_be_generic_open(chr);
> >      return chr;
> >  }
> >  
> > @@ -1994,7 +1978,6 @@ static CharDriverState *qemu_chr_open_win_file(HANDLE 
> > fd_out)
> >      s->hcom = fd_out;
> >      chr->opaque = s;
> >      chr->chr_write = win_chr_write;
> > -    qemu_chr_be_generic_open(chr);
> >      return chr;
> >  }
> >  
> > @@ -2329,6 +2312,8 @@ static CharDriverState *qemu_chr_open_udp_fd(int fd)
> >      chr->chr_write = udp_chr_write;
> >      chr->chr_update_read_handler = udp_chr_update_read_handler;
> >      chr->chr_close = udp_chr_close;
> > +    /* be isn't opened until we get a connection */
> > +    chr->explicit_be_open = true;
> >      return chr;
> >  }
> >  
> > @@ -2731,6 +2716,8 @@ static CharDriverState *qemu_chr_open_socket_fd(int 
> > fd, bool do_nodelay,
> >      chr->get_msgfd = tcp_get_msgfd;
> >      chr->chr_add_client = tcp_chr_add_client;
> >      chr->chr_add_watch = tcp_chr_add_watch;
> > +    /* be isn't opened until we get a connection */
> > +    chr->explicit_be_open = true;
> >  
> >      if (is_listen) {
> >          s->listen_fd = fd;
> > @@ -3325,6 +3312,12 @@ CharDriverState *qemu_chr_new_from_opts(QemuOpts 
> > *opts,
> >      if (!chr->filename)
> >          chr->filename = g_strdup(qemu_opt_get(opts, "backend"));
> >      chr->init = init;
> > +    /* if we didn't create the chardev via qmp_chardev_add, we
> > +     * need to send the OPENED event here
> > +     */
> > +    if (!chr->explicit_be_open) {
> > +        qemu_chr_be_event(chr, CHR_EVENT_OPENED);
> > +    }
> >      QTAILQ_INSERT_TAIL(&chardevs, chr, next);
> >  
> >      if (qemu_opt_get_bool(opts, "mux", 0)) {
> > @@ -3804,6 +3797,9 @@ ChardevReturn *qmp_chardev_add(const char *id, 
> > ChardevBackend *backend,
> >          if (!chr->filename) {
> >              chr->filename = 
> > g_strdup(ChardevBackendKind_lookup[backend->kind]);
> >          }
> > +        if (!chr->explicit_be_open) {
> > +            qemu_chr_be_event(chr, CHR_EVENT_OPENED);
> > +        }
> >          QTAILQ_INSERT_TAIL(&chardevs, chr, next);
> >          return ret;
> >      } else {
> > diff --git a/spice-qemu-char.c b/spice-qemu-char.c
> > index f10970c..6d147a7 100644
> > --- a/spice-qemu-char.c
> > +++ b/spice-qemu-char.c
> > @@ -255,6 +255,7 @@ static CharDriverState *chr_open(const char *subtype)
> >      chr->chr_add_watch = spice_chr_add_watch;
> >      chr->chr_close = spice_chr_close;
> >      chr->chr_set_fe_open = spice_chr_set_fe_open;
> > +    chr->explicit_be_open = true;
> >  
> >      QLIST_INSERT_HEAD(&spice_chars, s, next);
> >  
> > diff --git a/ui/console.c b/ui/console.c
> > index b30853f..54b192d 100644
> > --- a/ui/console.c
> > +++ b/ui/console.c
> > @@ -1746,7 +1746,6 @@ static void text_console_do_init(CharDriverState 
> > *chr, DisplayState *ds)
> >          s->t_attrib = s->t_attrib_default;
> >      }
> >  
> > -    qemu_chr_be_generic_open(chr);
> >      if (chr->init)
> >          chr->init(chr);
> >  }
> > diff --git a/ui/gtk.c b/ui/gtk.c
> > index 3bc2842..ef1bb71 100644
> > --- a/ui/gtk.c
> > +++ b/ui/gtk.c
> > @@ -1216,7 +1216,6 @@ static GSList *gd_vc_init(GtkDisplayState *s, 
> > VirtualConsole *vc, int index, GSL
> >  
> >      gtk_menu_shell_append(GTK_MENU_SHELL(view_menu), vc->menu_item);
> >  
> > -    qemu_chr_be_generic_open(vc->chr);
> >      if (vc->chr->init) {
> >          vc->chr->init(vc->chr);
> >      }
>