From dafee8907bcaa3ee580ebef4f76e7d62c14cd5c3 Mon Sep 17 00:00:00 2001
From: Alexander Graf <agraf@suse.de>
Date: Thu, 1 Apr 2010 17:36:23 +0200
Subject: [PATCH] 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]
---
 chardev/char-mux.c | 13 +++++++++++++
 chardev/char-mux.h |  3 +++
 2 files changed, 16 insertions(+)

diff --git a/chardev/char-mux.c b/chardev/char-mux.c
index 5547a36a0a..7b80dc8ad7 100644
--- a/chardev/char-mux.c
+++ b/chardev/char-mux.c
@@ -179,6 +179,15 @@ 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)
@@ -308,6 +317,10 @@ 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-mux.h b/chardev/char-mux.h
index 9a2fffce91..d5f419c8a9 100644
--- a/chardev/char-mux.h
+++ b/chardev/char-mux.h
@@ -35,6 +35,9 @@ 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;