qemu/0022-Make-char-muxer-more-robust-wrt-sma.patch

From 047016003be1f8b58e063551d6e890f2616e931e 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]
---
 qemu-char.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/qemu-char.c b/qemu-char.c
index 2c9940cea4..b6a9a32bf4 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -531,6 +531,9 @@ static CharDriverState *qemu_chr_open_null(const char *id,
 struct MuxDriver {
     CharBackend *backends[MAX_MUX];
     CharBackend chr;
+#if defined(TARGET_S390X)
+    QEMUTimer *accept_timer;
+#endif
     int focus;
     int mux_cnt;
     int term_got_escape;
@@ -694,6 +697,15 @@ static void mux_chr_accept_input(CharDriverState *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)
@@ -864,6 +876,10 @@ static CharDriverState *qemu_chr_open_mux(const char *id,
 
     chr->opaque = d;
     d->focus = -1;
+#if defined(TARGET_S390X)
+    d->accept_timer = qemu_new_timer_ns(vm_clock,
+                                     (QEMUTimerCB*)mux_chr_accept_input, chr);
+#endif
     chr->chr_free = mux_chr_free;
     chr->chr_write = mux_chr_write;
     chr->chr_accept_input = mux_chr_accept_input;