diff options
authorAlexander Graf <>2010-04-01 15:36:23 (GMT)
committerYury Usishchev <>2014-12-10 11:51:42 (GMT)
commit3180d55b5e2962b3c8f6f4f43050f25f0c719053 (patch)
parent6b35baeb5e2fd28665180ca97f989d367e99749e (diff)
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.
1 files changed, 16 insertions, 0 deletions
diff --git a/qemu-char.c b/qemu-char.c
index a8b01da..2780d14 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -403,6 +403,9 @@ typedef struct {
IOEventHandler *chr_event[MAX_MUX];
void *ext_opaque[MAX_MUX];
CharDriverState *drv;
+#if defined(TARGET_S390X)
+ QEMUTimer *accept_timer;
int focus;
int mux_cnt;
int term_got_escape;
@@ -562,6 +565,15 @@ static void mux_chr_accept_input(CharDriverState *chr)
&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);
+ }
static int mux_chr_can_read(void *opaque)
@@ -690,6 +702,10 @@ static CharDriverState *qemu_chr_open_mux(CharDriverState *drv)
chr->opaque = d;
d->drv = drv;
d->focus = -1;
+#if defined(TARGET_S390X)
+ d->accept_timer = qemu_new_timer_ns(vm_clock,
+ (QEMUTimerCB*)mux_chr_accept_input, chr);
chr->chr_write = mux_chr_write;
chr->chr_update_read_handler = mux_chr_update_read_handler;
chr->chr_accept_input = mux_chr_accept_input;