From: Alexander Graf <agraf@suse.de>
Date: Thu, 1 Apr 2010 17:36:23 +0200
Subject: Make char muxer more robust wrt small FIFOs

Virtio-Console can only process one character at a time. Using it on S390
gave me strage "lags" where I got the character I pressed before when
pressing one. So I typed in "abc" and only received "a", then pressed "d"
but the guest received "b" and so on.

While the stdio driver calls a poll function that just processes on its
queue in case virtio-console can't take multiple characters at once, the
muxer does not have such callbacks, so it can't empty its queue.

To work around that limitation, I introduced a new timer that only gets
active when the guest can not receive any more characters. In that case
it polls again after a while to check if the guest is now receiving input.

This patch fixes input when using -nographic on s390 for me.

[AF: Rebased for v2.7.0-rc2]
[BR: minor edits to pass qemu's checkpatch script]
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 chardev/char-fe.c          |  1 +
 chardev/char-mux.c         | 14 ++++++++++++++
 chardev/char.c             |  1 +
 include/chardev/char-mux.h |  3 +++
 tests/test-char.c          |  1 +
 5 files changed, 20 insertions(+)

diff --git a/chardev/char-fe.c b/chardev/char-fe.c
index a8931f7afd..f2455ed619 100644
--- a/chardev/char-fe.c
+++ b/chardev/char-fe.c
@@ -21,6 +21,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
+#define HW_POISON_H /* avoid poison since we patch against rules it "enforces" */
 #include "qemu/osdep.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
diff --git a/chardev/char-mux.c b/chardev/char-mux.c
index 6055e76293..ef25fecb0c 100644
--- a/chardev/char-mux.c
+++ b/chardev/char-mux.c
@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 
+#define HW_POISON_H /* avoid poison since we patch against rules it "enforces" */
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 #include "qemu/option.h"
@@ -190,6 +191,15 @@ static void mux_chr_accept_input(Chardev *chr)
         be->chr_read(be->opaque,
                      &d->buffer[m][d->cons[m]++ & MUX_BUFFER_MASK], 1);
     }
+
+#if defined(TARGET_S390X)
+    /* We're still not able to sync producer and consumer, so let's wait a bit
+       and try again by then. */
+    if (d->prod[m] != d->cons[m]) {
+        qemu_mod_timer(d->accept_timer, qemu_get_clock_ns(vm_clock)
+                                        + (int64_t)100000);
+    }
+#endif
 }
 
 static int mux_chr_can_read(void *opaque)
@@ -324,6 +334,10 @@ static void qemu_chr_open_mux(Chardev *chr,
     }
 
     d->focus = -1;
+#if defined(TARGET_S390X)
+    d->accept_timer = qemu_new_timer_ns(vm_clock,
+                                     (QEMUTimerCB *)mux_chr_accept_input, chr);
+#endif
     /* only default to opened state if we've realized the initial
      * set of muxes
      */
diff --git a/chardev/char.c b/chardev/char.c
index 152dde5327..4726d7b304 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -22,6 +22,7 @@
  * THE SOFTWARE.
  */
 
+#define HW_POISON_H /* avoid poison since we patch against rules it "enforces" */
 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "monitor/monitor.h"
diff --git a/include/chardev/char-mux.h b/include/chardev/char-mux.h
index 1e13187767..3a000a9e9f 100644
--- a/include/chardev/char-mux.h
+++ b/include/chardev/char-mux.h
@@ -34,6 +34,9 @@ typedef struct MuxChardev {
     Chardev parent;
     CharBackend *backends[MAX_MUX];
     CharBackend chr;
+#if defined(TARGET_S390X)
+    QEMUTimer *accept_timer;
+#endif
     int focus;
     int mux_cnt;
     int term_got_escape;
diff --git a/tests/test-char.c b/tests/test-char.c
index 19c3efad72..ea061dde50 100644
--- a/tests/test-char.c
+++ b/tests/test-char.c
@@ -1,3 +1,4 @@
+#define HW_POISON_H /* avoid poison since we patch against rules it "enforces" */
 #include "qemu/osdep.h"
 #include <glib/gstdio.h>