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[Qemu-devel] [PULL 06/15] char/spice: discard write() if backend is disc
From: |
Gerd Hoffmann |
Subject: |
[Qemu-devel] [PULL 06/15] char/spice: discard write() if backend is disconnected |
Date: |
Fri, 22 Feb 2019 08:53:17 +0100 |
From: Marc-André Lureau <address@hidden>
Most chardev backend handle write() as discarded data if underlying
system is disconnected. For unknown historical reasons, the Spice
backend has "reliable" write: it will wait until the client end is
reconnected to do further successful write().
To decide whether it make sense to wait until the client is
reconnected (or queue the writes), let's review Spice chardev usage
and handling of a disconnected client:
* spice vdagent
The agents reopen the virtio port on disconnect. In qemu side,
virtio_serial_close() will also discard pending data.
* usb redirection
A disconnect creates a device disconnection.
* smartcard emulation
Data is discarded in passthru_apdu_from_guest().
(Spice doesn't explicitly open the smartcard char device until
upcoming 0.14.2, commit 69a5cfc74131ec0459f2eb5a231139f5a69a8037)
* spice webdavd
The daemon will restart the service, and reopen the virtio port.
* spice ports (serial console, qemu monitor..)
Depends on the associated device or usage.
- serial, may be throttled or discarded on write, depending on
device
- QMP/HMP monitor have some CLOSED event handling, but want to
flush the write, which will finish when a new client connects.
On disconnect/reconnect, the client starts with fresh sessions. If it
is a seamless migration, the client disconnects after the source
migrated. The handling of source disconnect in qemu is thus irrelevant
for the Spice session migration.
For all these use cases, it is better to discard writes when the
client is disconnected, and require the vm-side device/agent to behave
correctly on CHR_EVENT_CLOSED, to stop reading and writing from
the spice chardev.
Signed-off-by: Marc-André Lureau <address@hidden>
Tested-by: Victor Toso <address@hidden>
Message-id: address@hidden
Signed-off-by: Gerd Hoffmann <address@hidden>
---
chardev/spice.c | 12 ++++++++++++
chardev/trace-events | 1 +
2 files changed, 13 insertions(+)
diff --git a/chardev/spice.c b/chardev/spice.c
index c2baeb5461fa..c68e60115bb1 100644
--- a/chardev/spice.c
+++ b/chardev/spice.c
@@ -208,6 +208,12 @@ static int spice_chr_write(Chardev *chr, const uint8_t
*buf, int len)
int read_bytes;
assert(s->datalen == 0);
+
+ if (!chr->be_open) {
+ trace_spice_chr_discard_write(len);
+ return len;
+ }
+
s->datapos = buf;
s->datalen = len;
spice_server_char_device_wakeup(&s->sin);
@@ -300,6 +306,12 @@ static void qemu_chr_open_spice_vmc(Chardev *chr,
}
*be_opened = false;
+#if SPICE_SERVER_VERSION < 0x000e02
+ /* Spice < 0.14.2 doesn't explicitly open smartcard chardev */
+ if (strcmp(type, "smartcard") == 0) {
+ *be_opened = true;
+ }
+#endif
chr_open(chr, type);
}
diff --git a/chardev/trace-events b/chardev/trace-events
index d0e5f3bbc1a7..b8a759634420 100644
--- a/chardev/trace-events
+++ b/chardev/trace-events
@@ -10,6 +10,7 @@ wct_cmd_other(const char *cmd) "%s"
wct_speed(int speed) "%d"
# chardev/spice.c
+spice_chr_discard_write(int len) "spice chr write discarded %d"
spice_vmc_write(ssize_t out, int len) "spice wrote %zd of requested %d"
spice_vmc_read(int bytes, int len) "spice read %d of requested %d"
spice_vmc_register_interface(void *scd) "spice vmc registered interface %p"
--
2.9.3
- [Qemu-devel] [PULL 02/15] spice: set device address and device display ID in QXL interface, (continued)
- [Qemu-devel] [PULL 02/15] spice: set device address and device display ID in QXL interface, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 03/15] sdl2: drop qemu_input_event_send_key_qcode call, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 14/15] spice: use a default name for the server, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 10/15] char: move SpiceChardev and open_spice_port() to spice.h header, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 07/15] spice: avoid spice runtime assert, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 11/15] char: register spice ports after spice started, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 08/15] spice: merge options lists, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 05/15] char/spice: trigger HUP event, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 01/15] kbd-state: don't block auto-repeat events, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 12/15] build-sys: add gio-2.0 check, Gerd Hoffmann, 2019/02/22
- [Qemu-devel] [PULL 06/15] char/spice: discard write() if backend is disconnected,
Gerd Hoffmann <=
- [Qemu-devel] [PULL 15/15] display: add -display spice-app launching a Spice client, Gerd Hoffmann, 2019/02/22
- Re: [Qemu-devel] [PULL 00/15] Ui 20190222 patches, Peter Maydell, 2019/02/25