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[Qemu-devel] [PATCH v2 03/12] char/spice: discard write() if backend is
From: |
Marc-André Lureau |
Subject: |
[Qemu-devel] [PATCH v2 03/12] char/spice: discard write() if backend is disconnected |
Date: |
Thu, 20 Dec 2018 18:15:44 +0400 |
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>
---
chardev/spice.c | 12 ++++++++++++
chardev/trace-events | 1 +
2 files changed, 13 insertions(+)
diff --git a/chardev/spice.c b/chardev/spice.c
index c2baeb5461..c68e60115b 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 d0e5f3bbc1..b8a7596344 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"
--
2.20.1.2.gb21ebb671b
- Re: [Qemu-devel] [PATCH v2 10/12] qapi: document DisplayType enum, (continued)
- [Qemu-devel] [PATCH v2 07/12] char: move SpiceChardev and open_spice_port() to spice.h header, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 11/12] spice: use a default name for the server, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 06/12] spice: do not stop spice if VM is paused, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 04/12] spice: avoid spice runtime assert, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 09/12] build-sys: add gio-2.0 check, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 02/12] char/spice: trigger HUP event, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 08/12] char: register spice ports after spice started, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 12/12] display: add -display spice-app launching a Spice client, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 01/12] configure: bump spice-server required version to 0.12.5, Marc-André Lureau, 2018/12/20
- [Qemu-devel] [PATCH v2 03/12] char/spice: discard write() if backend is disconnected,
Marc-André Lureau <=
- [Qemu-devel] [PATCH v2 05/12] spice: merge options lists, Marc-André Lureau, 2018/12/20
- Re: [Qemu-devel] [PATCH v2 00/12] spice: add -display spice-app, setup and launch a Spice client, Victor Toso, 2018/12/21