Am 04.05.2010 um 15:44 schrieb Anthony Liguori <anth...@codemonkey.ws>:
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.
There is no polling for the muxer. That's why it never knows when
virtio-console can receive again.
This patch basically adfs timer based polling for that exact case.
Alex
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;
