On 04/20/2010 11:56 AM, Alexander Graf wrote:
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.
I think this is really a kvm issue. I assume it's because s390 idles in
the kernel so you never drop to userspace to repoll the descriptor.
A timer is a hacky solution. You really need to use an io thread to
solve this and then you need to switch away from qemu_set_fd_handler2 to
qemu_set_fd_handler() and make sure that the later breaks select
whenever it's invoked.
Regards,
Anthony Liguori
---
Please consider for stable.
---
qemu-char.c | 10 ++++++++++
1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/qemu-char.c b/qemu-char.c
index 05df971..ce9df3a 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -235,6 +235,7 @@ typedef struct {
IOEventHandler *chr_event[MAX_MUX];
void *ext_opaque[MAX_MUX];
CharDriverState *drv;
+ QEMUTimer *accept_timer;
int focus;
int mux_cnt;
int term_got_escape;
@@ -396,6 +397,13 @@ static void mux_chr_accept_input(CharDriverState *chr)
d->chr_read[m](d->ext_opaque[m],
&d->buffer[m][d->cons[m]++& MUX_BUFFER_MASK], 1);
}
+
+ /* 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(vm_clock)
+ + (int64_t)100000);
+ }
}
static int mux_chr_can_read(void *opaque)
@@ -478,6 +486,8 @@ static CharDriverState *qemu_chr_open_mux(CharDriverState
*drv)
chr->opaque = d;
d->drv = drv;
d->focus = -1;
+ d->accept_timer = qemu_new_timer(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;
