This patch implements multiplexing capability of several backend
devices, which opens up an opportunity to use a single frontend
device on the guest, which can be manipulated from several
backend devices.
The idea of the change is trivial: keep list of backend devices
(up to 4), init them on demand and forward data buffer back and
forth.
Patch implements another multiplexer type `mux-be`. The following
is QEMU command line example:
-chardev mux-be,id=mux0 \
-chardev socket,path=/tmp/sock,server=on,wait=off,id=sock0,mux-be-id=mux0 \
-chardev vc,id=vc0,mux-be-id=mux0 \
-device virtconsole,chardev=mux0 \
-vnc 0.0.0.0:0
Which creates 2 backend devices: text virtual console (`vc0`) and a
socket (`sock0`) connected to the single virtio hvc console with the
backend multiplexer (`mux0`) help. `vc0` renders text to an image,
which can be shared over the VNC protocol. `sock0` is a socket
backend which provides biderectional communication to the virtio hvc
console.
Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
---
chardev/char-fe.c | 9 ++
chardev/char-mux-be.c | 290 +++++++++++++++++++++++++++++++++++++
chardev/char.c | 56 +++++--
chardev/chardev-internal.h | 34 ++++-
chardev/meson.build | 1 +
include/chardev/char.h | 1 +
qapi/char.json | 25 ++++
7 files changed, 403 insertions(+), 13 deletions(-)
create mode 100644 chardev/char-mux-be.c
diff --git a/chardev/char-fe.c b/chardev/char-fe.c
index a2b5bff39fd9..2f794674563b 100644
--- a/chardev/char-fe.c
+++ b/chardev/char-fe.c
@@ -200,6 +200,12 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
if (!mux_fe_chr_attach_frontend(d, b, &tag, errp)) {
return false;
}
+ } else if (CHARDEV_IS_MUX_BE(s)) {
+ MuxBeChardev *d = MUX_BE_CHARDEV(s);
+
+ if (!mux_be_chr_attach_frontend(d, b, errp)) {
+ return false;
+ }
} else if (s->be) {
error_setg(errp, "chardev '%s' is already in use", s->label);
return false;
@@ -226,6 +232,9 @@ void qemu_chr_fe_deinit(CharBackend *b, bool del)
if (CHARDEV_IS_MUX_FE(b->chr)) {
MuxFeChardev *d = MUX_FE_CHARDEV(b->chr);
mux_fe_chr_detach_frontend(d, b->tag);
+ } else if (CHARDEV_IS_MUX_BE(b->chr)) {
+ MuxBeChardev *d = MUX_BE_CHARDEV(b->chr);
+ mux_be_chr_detach_frontend(d);
}
if (del) {
Object *obj = OBJECT(b->chr);
diff --git a/chardev/char-mux-be.c b/chardev/char-mux-be.c
new file mode 100644
index 000000000000..64a4f2c00034
--- /dev/null
+++ b/chardev/char-mux-be.c
@@ -0,0 +1,290 @@
+/*
+ * QEMU Character Backend Multiplexer
+ *
+ * Author: Roman Penyaev <r.peniaev@gmail.com>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qemu/module.h"
+#include "qemu/option.h"
+#include "qemu/cutils.h"
+#include "chardev/char.h"
+#include "sysemu/block-backend.h"
+#include "qapi/qapi-commands-control.h"
+#include "qapi/clone-visitor.h"
+#include "qapi/qapi-builtin-visit.h"
+#include "chardev-internal.h"
+
+/*
+ * MUX-BE driver for multiplexing 1 frontend device with N backend devices
+ */
+
+/*
+ * Write to all backends. Different backend devices accept data with
+ * various rate, so it is quite possible that one device returns less,
+ * then others. In this case we return minimum to the caller,
+ * expecting caller will repeat operation soon. When repeat happens
+ * send to the devices which consume data faster must be avoided
+ * for obvious reasons not to send data, which was already sent.
+ */
+static int mux_be_chr_write_to_all(MuxBeChardev *d, const uint8_t *buf, int len)
+{
+ int r, i, ret = len;
+ unsigned int written;
+
+ for (i = 0; i < d->be_cnt; i++) {
+ written = d->be_written[i] - d->be_min_written;
+ if (written) {
+ /* Written in the previous call so take into account */
+ ret = MIN(written, ret);
+ continue;
+ }
+ r = qemu_chr_fe_write(&d->backends[i], buf, len);
+ if (r < 0 && errno == EAGAIN) {
+ /*
+ * Fail immediately if write would block. Expect to be called
+ * soon on watch wake up.
+ */
+ return r;
+ } else if (r < 0) {
+ /*
+ * Ignore all other errors and pretend the entire buffer is
+ * written to avoid this chardev being watched. This device
+ * becomes disabled until the following write succeeds, but
+ * writing continues to others.
+ */
+ r = len;
+ }
+ d->be_written[i] += r;
+ ret = MIN(r, ret);
+ }
+ d->be_min_written += ret;
+
+ return ret;
+}
+
+/* Called with chr_write_lock held. */
+static int mux_be_chr_write(Chardev *chr, const uint8_t *buf, int len)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(chr);
+ return mux_be_chr_write_to_all(d, buf, len);
+}
+
+static void mux_be_chr_send_event(MuxBeChardev *d, QEMUChrEvent event)
+{
+ CharBackend *fe = d->frontend;
+
+ if (fe && fe->chr_event) {
+ fe->chr_event(fe->opaque, event);
+ }
+}
+
+static void mux_be_chr_be_event(Chardev *chr, QEMUChrEvent event)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(chr);
+
+ mux_be_chr_send_event(d, event);
+}
+
+static int mux_be_chr_can_read(void *opaque)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(opaque);
+ CharBackend *fe = d->frontend;
+
+ if (fe && fe->chr_can_read) {
+ return fe->chr_can_read(fe->opaque);
+ }
+
+ return 0;
+}
+
+static void mux_be_chr_read(void *opaque, const uint8_t *buf, int size)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(opaque);
+ CharBackend *fe = d->frontend;
+
+ if (fe && fe->chr_read) {
+ fe->chr_read(fe->opaque, buf, size);
+ }
+}
+
+void mux_be_chr_send_all_event(MuxBeChardev *d, QEMUChrEvent event)
+{
+ mux_be_chr_send_event(d, event);
+}
+
+static void mux_be_chr_event(void *opaque, QEMUChrEvent event)
+{
+ mux_chr_send_all_event(CHARDEV(opaque), event);
+}
+
+static GSource *mux_be_chr_add_watch(Chardev *s, GIOCondition cond)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(s);
+ Chardev *chr;
+ ChardevClass *cc;
+ unsigned int written;
+ int i;
+
+ for (i = 0; i < d->be_cnt; i++) {
+ written = d->be_written[i] - d->be_min_written;
+ if (written) {
+ /* We skip the device with already written buffer */
+ continue;
+ }
+
+ /*
+ * The first device that has no data written to it must be
+ * the device that recently returned EAGAIN and should be
+ * watched.
+ */
+
+ chr = qemu_chr_fe_get_driver(&d->backends[i]);
+ cc = CHARDEV_GET_CLASS(chr);
+
+ if (!cc->chr_add_watch) {
+ return NULL;
+ }
+
+ return cc->chr_add_watch(chr, cond);
+ }
+
+ return NULL;
+}
+
+bool mux_be_chr_attach_chardev(MuxBeChardev *d, Chardev *chr, Error **errp)
+{
+ bool ret;
+
+ if (d->be_cnt >= MAX_MUX) {
+ error_setg(errp, "too many uses of multiplexed chardev '%s'"
+ " (maximum is " stringify(MAX_MUX) ")",
+ d->parent.label);
+ return false;
+ }
+ ret = qemu_chr_fe_init(&d->backends[d->be_cnt], chr, errp);
+ if (ret) {
+ /* Catch up with what was already written */
+ d->be_written[d->be_cnt] = d->be_min_written;
+ d->be_cnt += 1;
+ }
+
+ return ret;
+}
+
+static void char_mux_be_finalize(Object *obj)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(obj);
+ CharBackend *fe = d->frontend;
+ int i;
+
+ if (fe) {
+ fe->chr = NULL;
+ }
+ for (i = 0; i < d->be_cnt; i++) {
+ qemu_chr_fe_deinit(&d->backends[i], false);
+ }
+}
+
+static void mux_be_chr_update_read_handlers(Chardev *chr)
+{
+ MuxBeChardev *d = MUX_BE_CHARDEV(chr);
+ int i;
+
+ for (i = 0; i < d->be_cnt; i++) {
+ /* Fix up the real driver with mux routines */
+ qemu_chr_fe_set_handlers_full(&d->backends[i],
+ mux_be_chr_can_read,
+ mux_be_chr_read,
+ mux_be_chr_event,
+ NULL,
+ chr,
+ chr->gcontext, true, false);
+ }
+}
+
+bool mux_be_chr_attach_frontend(MuxBeChardev *d, CharBackend *b, Error **errp)
+{
+ if (d->frontend) {
+ error_setg(errp,
+ "multiplexed chardev '%s' is already used "
+ "for multiplexing", d->parent.label);
+ return false;
+ }
+ d->frontend = b;
+
+ return true;
+}
+
+void mux_be_chr_detach_frontend(MuxBeChardev *d)
+{
+ d->frontend = NULL;
+}
+
+static void qemu_chr_open_mux_be(Chardev *chr,
+ ChardevBackend *backend,
+ bool *be_opened,
+ Error **errp)
+{
+ /*
+ * Only default to opened state if we've realized the initial
+ * set of muxes
+ */
+ *be_opened = mux_is_opened();
+}
+
+static void qemu_chr_parse_mux_be(QemuOpts *opts, ChardevBackend *backend,
+ Error **errp)
+{
+ ChardevMuxBe *mux;
+
+ backend->type = CHARDEV_BACKEND_KIND_MUX_BE;
+ mux = backend->u.mux_be.data = g_new0(ChardevMuxBe, 1);
+ qemu_chr_parse_common(opts, qapi_ChardevMuxBe_base(mux));
+}
+
+static void char_mux_be_class_init(ObjectClass *oc, void *data)
+{
+ ChardevClass *cc = CHARDEV_CLASS(oc);
+
+ cc->parse = qemu_chr_parse_mux_be;
+ cc->open = qemu_chr_open_mux_be;
+ cc->chr_write = mux_be_chr_write;
+ cc->chr_add_watch = mux_be_chr_add_watch;
+ cc->chr_be_event = mux_be_chr_be_event;
+ cc->chr_update_read_handler = mux_be_chr_update_read_handlers;
+}
+
+static const TypeInfo char_mux_be_type_info = {
+ .name = TYPE_CHARDEV_MUX_BE,
+ .parent = TYPE_CHARDEV,
+ .class_init = char_mux_be_class_init,
+ .instance_size = sizeof(MuxBeChardev),
+ .instance_finalize = char_mux_be_finalize,
+};
+
+static void register_types(void)
+{
+ type_register_static(&char_mux_be_type_info);
+}
+
+type_init(register_types);
diff --git a/chardev/char.c b/chardev/char.c
index cffe60860589..58fa8ac70a1e 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -341,6 +341,9 @@ static bool qemu_chr_is_busy(Chardev *s)
if (CHARDEV_IS_MUX_FE(s)) {
MuxFeChardev *d = MUX_FE_CHARDEV(s);
return d->mux_bitset != 0;
+ } else if (CHARDEV_IS_MUX_BE(s)) {
+ MuxBeChardev *d = MUX_BE_CHARDEV(s);
+ return d->frontend != NULL;
} else {
return s->be != NULL;
}
@@ -648,7 +651,8 @@ static Chardev *__qemu_chr_new_from_opts(QemuOpts *opts, GMainContext *context,
ChardevBackend *backend = NULL;
const char *name = qemu_opt_get(opts, "backend");
const char *id = qemu_opts_id(opts);
- char *bid = NULL;
+ const char *mux_be_id = NULL;
+ char *mux_fe_id = NULL;
if (name && is_help_option(name)) {
GString *str = g_string_new("");
@@ -676,10 +680,16 @@ static Chardev *__qemu_chr_new_from_opts(QemuOpts *opts, GMainContext *context,
}
if (qemu_opt_get_bool(opts, "mux", 0)) {
- bid = g_strdup_printf("%s-base", id);
+ mux_fe_id = g_strdup_printf("%s-base", id);
+ }
+ mux_be_id = qemu_opt_get(opts, "mux-be-id");
+ if (mux_be_id && mux_fe_id) {
+ error_setg(errp, "chardev: mux and mux-be can't be used for the same "
+ "device");
+ goto out;
}
- chr = qemu_chardev_new(bid ? bid : id,
+ chr = qemu_chardev_new(mux_fe_id ? mux_fe_id : id,
object_class_get_name(OBJECT_CLASS(cc)),
backend, context, errp);
if (chr == NULL) {
@@ -687,25 +697,40 @@ static Chardev *__qemu_chr_new_from_opts(QemuOpts *opts, GMainContext *context,
}
base = chr;
- if (bid) {
+ if (mux_fe_id) {
Chardev *mux;
qapi_free_ChardevBackend(backend);
backend = g_new0(ChardevBackend, 1);
backend->type = CHARDEV_BACKEND_KIND_MUX;
backend->u.mux.data = g_new0(ChardevMux, 1);
- backend->u.mux.data->chardev = g_strdup(bid);
+ backend->u.mux.data->chardev = g_strdup(mux_fe_id);
mux = qemu_chardev_new(id, TYPE_CHARDEV_MUX_FE, backend, context, errp);
if (mux == NULL) {
- object_unparent(OBJECT(chr));
- chr = NULL;
- goto out;
+ goto unparent_and_out;
}
chr = mux;
+ } else if (mux_be_id) {
+ Chardev *s;
+
+ s = qemu_chr_find(mux_be_id);
+ if (!s) {
+ error_setg(errp, "chardev: mux-be device can't be found by id '%s'",
+ mux_be_id);
+ goto unparent_and_out;
+ }
+ if (!CHARDEV_IS_MUX_BE(s)) {
+ error_setg(errp, "chardev: device '%s' is not a multiplexer device"
+ " of 'mux-be' type", mux_be_id);
+ goto unparent_and_out;
+ }
+ if (!mux_be_chr_attach_chardev(MUX_BE_CHARDEV(s), chr, errp)) {
+ goto unparent_and_out;
+ }
}
out:
qapi_free_ChardevBackend(backend);
- g_free(bid);
+ g_free(mux_fe_id);
if (replay && base) {
/* RR should be set on the base device, not the mux */
@@ -713,6 +738,11 @@ out:
}
return chr;
+
+unparent_and_out:
+ object_unparent(OBJECT(chr));
+ chr = NULL;
+ goto out;
}
Chardev *qemu_chr_new_from_opts(QemuOpts *opts, GMainContext *context,
@@ -1114,7 +1144,7 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
return NULL;
}
- if (CHARDEV_IS_MUX_FE(chr)) {
+ if (CHARDEV_IS_MUX_FE(chr) || CHARDEV_IS_MUX_BE(chr)) {
error_setg(errp, "Mux device hotswap not supported yet");
return NULL;
}
@@ -1302,7 +1332,7 @@ static int chardev_options_parsed_cb(Object *child, void *opaque)
{
Chardev *chr = (Chardev *)child;
- if (!chr->be_open && CHARDEV_IS_MUX_FE(chr)) {
+ if (!chr->be_open && (CHARDEV_IS_MUX_FE(chr) || CHARDEV_IS_MUX_BE(chr))) {
open_muxes(chr);
}
@@ -1329,8 +1359,10 @@ void mux_chr_send_all_event(Chardev *chr, QEMUChrEvent event)
if (CHARDEV_IS_MUX_FE(chr)) {
MuxFeChardev *d = MUX_FE_CHARDEV(chr);
-
mux_fe_chr_send_all_event(d, event);
+ } else if (CHARDEV_IS_MUX_BE(chr)) {
+ MuxBeChardev *d = MUX_BE_CHARDEV(chr);
+ mux_be_chr_send_all_event(d, event);
}
}
diff --git a/chardev/chardev-internal.h b/chardev/chardev-internal.h
index 94c8d07ac235..8ea1258f8ff4 100644
--- a/chardev/chardev-internal.h
+++ b/chardev/chardev-internal.h
@@ -35,7 +35,9 @@
struct MuxFeChardev {
Chardev parent;
+ /* Linked frontends */
CharBackend *backends[MAX_MUX];
+ /* Linked backend */
CharBackend chr;
unsigned long mux_bitset;
int focus;
@@ -54,10 +56,36 @@ struct MuxFeChardev {
};
typedef struct MuxFeChardev MuxFeChardev;
+struct MuxBeChardev {
+ Chardev parent;
+ /* Linked frontend */
+ CharBackend *frontend;
+ /* Linked backends */
+ CharBackend backends[MAX_MUX];
+ /*
+ * Number of backends attached to this mux. Once attached, a
+ * backend can't be detached, so the counter is only increasing.
+ * To safely remove a backend, mux has to be removed first.
+ */
+ unsigned int be_cnt;
+ /*
+ * Counters of written bytes from a single frontend device
+ * to multiple backend devices.
+ */
+ unsigned int be_written[MAX_MUX];
+ unsigned int be_min_written;
+};
+typedef struct MuxBeChardev MuxBeChardev;
+
DECLARE_INSTANCE_CHECKER(MuxFeChardev, MUX_FE_CHARDEV,
TYPE_CHARDEV_MUX_FE)
-#define CHARDEV_IS_MUX_FE(chr) \
+DECLARE_INSTANCE_CHECKER(MuxBeChardev, MUX_BE_CHARDEV,
+ TYPE_CHARDEV_MUX_BE)
+
+#define CHARDEV_IS_MUX_FE(chr) \
object_dynamic_cast(OBJECT(chr), TYPE_CHARDEV_MUX_FE)
+#define CHARDEV_IS_MUX_BE(chr) \
+ object_dynamic_cast(OBJECT(chr), TYPE_CHARDEV_MUX_BE)
void mux_chr_send_all_event(Chardev *chr, QEMUChrEvent event);
@@ -67,6 +95,10 @@ void mux_fe_chr_send_all_event(MuxFeChardev *d, QEMUChrEvent event);
bool mux_fe_chr_attach_frontend(MuxFeChardev *d, CharBackend *b,
unsigned int *tag, Error **errp);
bool mux_fe_chr_detach_frontend(MuxFeChardev *d, unsigned int tag);
+void mux_be_chr_send_all_event(MuxBeChardev *d, QEMUChrEvent event);
+bool mux_be_chr_attach_chardev(MuxBeChardev *d, Chardev *chr, Error **errp);
+bool mux_be_chr_attach_frontend(MuxBeChardev *d, CharBackend *b, Error **errp);
+void mux_be_chr_detach_frontend(MuxBeChardev *d);
Object *get_chardevs_root(void);
diff --git a/chardev/meson.build b/chardev/meson.build
index 778444a00ca6..3a9f5565372b 100644
--- a/chardev/meson.build
+++ b/chardev/meson.build
@@ -3,6 +3,7 @@ chardev_ss.add(files(
'char-file.c',
'char-io.c',
'char-mux-fe.c',
+ 'char-mux-be.c',
'char-null.c',
'char-pipe.c',
'char-ringbuf.c',
diff --git a/include/chardev/char.h b/include/chardev/char.h
index 0bec974f9d73..c58c11c4eeaf 100644
--- a/include/chardev/char.h
+++ b/include/chardev/char.h
@@ -232,6 +232,7 @@ OBJECT_DECLARE_TYPE(Chardev, ChardevClass, CHARDEV)
#define TYPE_CHARDEV_NULL "chardev-null"
#define TYPE_CHARDEV_MUX_FE "chardev-mux"
+#define TYPE_CHARDEV_MUX_BE "chardev-mux-be"
#define TYPE_CHARDEV_RINGBUF "chardev-ringbuf"
#define TYPE_CHARDEV_PTY "chardev-pty"
#define TYPE_CHARDEV_CONSOLE "chardev-console"
diff --git a/qapi/char.json b/qapi/char.json
index fb0dedb24383..cdec8f9cf4e2 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -336,6 +336,17 @@
'data': { 'chardev': 'str' },
'base': 'ChardevCommon' }
+##
+# @ChardevMuxBe:
+#
+# Configuration info for mux-be chardevs.
+#
+# Since: 9.2
+##
+{ 'struct': 'ChardevMuxBe',
+ 'data': { },
+ 'base': 'ChardevCommon' }
+
##
# @ChardevStdio:
#
@@ -483,6 +494,8 @@
#
# @mux: (since 1.5)
#
+# @mux-be: (since 9.2)
+#
# @msmouse: emulated Microsoft serial mouse (since 1.5)
#
# @wctablet: emulated Wacom Penpartner serial tablet (since 2.9)
@@ -525,6 +538,7 @@
'pty',
'null',
'mux',
+ 'mux-be',
'msmouse',
'wctablet',
{ 'name': 'braille', 'if': 'CONFIG_BRLAPI' },
@@ -599,6 +613,16 @@
{ 'struct': 'ChardevMuxWrapper',
'data': { 'data': 'ChardevMux' } }
+##
+# @ChardevMuxBeWrapper:
+#
+# @data: Configuration info for mux-be chardevs
+#
+# Since: 9.2
+##
+{ 'struct': 'ChardevMuxBeWrapper',
+ 'data': { 'data': 'ChardevMuxBe' } }
+
##
# @ChardevStdioWrapper:
#
@@ -707,6 +731,7 @@
'pty': 'ChardevPtyWrapper',
'null': 'ChardevCommonWrapper',
'mux': 'ChardevMuxWrapper',
+ 'mux-be': 'ChardevMuxBeWrapper',
'msmouse': 'ChardevCommonWrapper',
'wctablet': 'ChardevCommonWrapper',
'braille': { 'type': 'ChardevCommonWrapper',
--
2.34.1
Hi On Wed, Oct 16, 2024 at 2:29 PM Roman Penyaev <r.peniaev@gmail.com> wrote: > This patch implements multiplexing capability of several backend > devices, which opens up an opportunity to use a single frontend > device on the guest, which can be manipulated from several > backend devices. > > The idea of the change is trivial: keep list of backend devices > (up to 4), init them on demand and forward data buffer back and > forth. > > Patch implements another multiplexer type `mux-be`. The following > is QEMU command line example: > > -chardev mux-be,id=mux0 \ > -chardev > socket,path=/tmp/sock,server=on,wait=off,id=sock0,mux-be-id=mux0 \ > -chardev vc,id=vc0,mux-be-id=mux0 \ > I am not sure about adding "mux-be-id" to all chardev. It avoids the issue of expressing a list of ids in mux-be though (while it may have potential loop!) Markus, do you have a suggestion to take an array of chardev ids as a CLI option? It looks like we could require QAPIfy -chardev from Kevin here.. thanks -device virtconsole,chardev=mux0 \ > -vnc 0.0.0.0:0 > > Which creates 2 backend devices: text virtual console (`vc0`) and a > socket (`sock0`) connected to the single virtio hvc console with the > backend multiplexer (`mux0`) help. `vc0` renders text to an image, > which can be shared over the VNC protocol. `sock0` is a socket > backend which provides biderectional communication to the virtio hvc > console. > > Signed-off-by: Roman Penyaev <r.peniaev@gmail.com> > Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com> > Cc: qemu-devel@nongnu.org > --- > chardev/char-fe.c | 9 ++ > chardev/char-mux-be.c | 290 +++++++++++++++++++++++++++++++++++++ > chardev/char.c | 56 +++++-- > chardev/chardev-internal.h | 34 ++++- > chardev/meson.build | 1 + > include/chardev/char.h | 1 + > qapi/char.json | 25 ++++ > 7 files changed, 403 insertions(+), 13 deletions(-) > create mode 100644 chardev/char-mux-be.c > > diff --git a/chardev/char-fe.c b/chardev/char-fe.c > index a2b5bff39fd9..2f794674563b 100644 > --- a/chardev/char-fe.c > +++ b/chardev/char-fe.c > @@ -200,6 +200,12 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, > Error **errp) > if (!mux_fe_chr_attach_frontend(d, b, &tag, errp)) { > return false; > } > + } else if (CHARDEV_IS_MUX_BE(s)) { > + MuxBeChardev *d = MUX_BE_CHARDEV(s); > + > + if (!mux_be_chr_attach_frontend(d, b, errp)) { > + return false; > + } > } else if (s->be) { > error_setg(errp, "chardev '%s' is already in use", s->label); > return false; > @@ -226,6 +232,9 @@ void qemu_chr_fe_deinit(CharBackend *b, bool del) > if (CHARDEV_IS_MUX_FE(b->chr)) { > MuxFeChardev *d = MUX_FE_CHARDEV(b->chr); > mux_fe_chr_detach_frontend(d, b->tag); > + } else if (CHARDEV_IS_MUX_BE(b->chr)) { > + MuxBeChardev *d = MUX_BE_CHARDEV(b->chr); > + mux_be_chr_detach_frontend(d); > } > if (del) { > Object *obj = OBJECT(b->chr); > diff --git a/chardev/char-mux-be.c b/chardev/char-mux-be.c > new file mode 100644 > index 000000000000..64a4f2c00034 > --- /dev/null > +++ b/chardev/char-mux-be.c > @@ -0,0 +1,290 @@ > +/* > + * QEMU Character Backend Multiplexer > + * > + * Author: Roman Penyaev <r.peniaev@gmail.com> > + * > + * Permission is hereby granted, free of charge, to any person obtaining > a copy > + * of this software and associated documentation files (the "Software"), > to deal > + * in the Software without restriction, including without limitation the > rights > + * to use, copy, modify, merge, publish, distribute, sublicense, and/or > sell > + * copies of the Software, and to permit persons to whom the Software is > + * furnished to do so, subject to the following conditions: > + * > + * The above copyright notice and this permission notice shall be > included in > + * all copies or substantial portions of the Software. > + * > + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, > EXPRESS OR > + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF > MERCHANTABILITY, > + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL > + * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR > OTHER > + * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, > ARISING FROM, > + * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS > IN > + * THE SOFTWARE. > + */ > + > +#include "qemu/osdep.h" > +#include "qapi/error.h" > +#include "qemu/module.h" > +#include "qemu/option.h" > +#include "qemu/cutils.h" > +#include "chardev/char.h" > +#include "sysemu/block-backend.h" > +#include "qapi/qapi-commands-control.h" > +#include "qapi/clone-visitor.h" > +#include "qapi/qapi-builtin-visit.h" > +#include "chardev-internal.h" > + > +/* > + * MUX-BE driver for multiplexing 1 frontend device with N backend devices > + */ > + > +/* > + * Write to all backends. Different backend devices accept data with > + * various rate, so it is quite possible that one device returns less, > + * then others. In this case we return minimum to the caller, > + * expecting caller will repeat operation soon. When repeat happens > + * send to the devices which consume data faster must be avoided > + * for obvious reasons not to send data, which was already sent. > + */ > +static int mux_be_chr_write_to_all(MuxBeChardev *d, const uint8_t *buf, > int len) > +{ > + int r, i, ret = len; > + unsigned int written; > + > + for (i = 0; i < d->be_cnt; i++) { > + written = d->be_written[i] - d->be_min_written; > + if (written) { > + /* Written in the previous call so take into account */ > + ret = MIN(written, ret); > + continue; > + } > + r = qemu_chr_fe_write(&d->backends[i], buf, len); > + if (r < 0 && errno == EAGAIN) { > + /* > + * Fail immediately if write would block. Expect to be called > + * soon on watch wake up. > + */ > + return r; > + } else if (r < 0) { > + /* > + * Ignore all other errors and pretend the entire buffer is > + * written to avoid this chardev being watched. This device > + * becomes disabled until the following write succeeds, but > + * writing continues to others. > + */ > + r = len; > + } > + d->be_written[i] += r; > + ret = MIN(r, ret); > + } > + d->be_min_written += ret; > + > + return ret; > +} > + > +/* Called with chr_write_lock held. */ > +static int mux_be_chr_write(Chardev *chr, const uint8_t *buf, int len) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(chr); > + return mux_be_chr_write_to_all(d, buf, len); > +} > + > +static void mux_be_chr_send_event(MuxBeChardev *d, QEMUChrEvent event) > +{ > + CharBackend *fe = d->frontend; > + > + if (fe && fe->chr_event) { > + fe->chr_event(fe->opaque, event); > + } > +} > + > +static void mux_be_chr_be_event(Chardev *chr, QEMUChrEvent event) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(chr); > + > + mux_be_chr_send_event(d, event); > +} > + > +static int mux_be_chr_can_read(void *opaque) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(opaque); > + CharBackend *fe = d->frontend; > + > + if (fe && fe->chr_can_read) { > + return fe->chr_can_read(fe->opaque); > + } > + > + return 0; > +} > + > +static void mux_be_chr_read(void *opaque, const uint8_t *buf, int size) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(opaque); > + CharBackend *fe = d->frontend; > + > + if (fe && fe->chr_read) { > + fe->chr_read(fe->opaque, buf, size); > + } > +} > + > +void mux_be_chr_send_all_event(MuxBeChardev *d, QEMUChrEvent event) > +{ > + mux_be_chr_send_event(d, event); > +} > + > +static void mux_be_chr_event(void *opaque, QEMUChrEvent event) > +{ > + mux_chr_send_all_event(CHARDEV(opaque), event); > +} > + > +static GSource *mux_be_chr_add_watch(Chardev *s, GIOCondition cond) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(s); > + Chardev *chr; > + ChardevClass *cc; > + unsigned int written; > + int i; > + > + for (i = 0; i < d->be_cnt; i++) { > + written = d->be_written[i] - d->be_min_written; > + if (written) { > + /* We skip the device with already written buffer */ > + continue; > + } > + > + /* > + * The first device that has no data written to it must be > + * the device that recently returned EAGAIN and should be > + * watched. > + */ > + > + chr = qemu_chr_fe_get_driver(&d->backends[i]); > + cc = CHARDEV_GET_CLASS(chr); > + > + if (!cc->chr_add_watch) { > + return NULL; > + } > + > + return cc->chr_add_watch(chr, cond); > + } > + > + return NULL; > +} > + > +bool mux_be_chr_attach_chardev(MuxBeChardev *d, Chardev *chr, Error > **errp) > +{ > + bool ret; > + > + if (d->be_cnt >= MAX_MUX) { > + error_setg(errp, "too many uses of multiplexed chardev '%s'" > + " (maximum is " stringify(MAX_MUX) ")", > + d->parent.label); > + return false; > + } > + ret = qemu_chr_fe_init(&d->backends[d->be_cnt], chr, errp); > + if (ret) { > + /* Catch up with what was already written */ > + d->be_written[d->be_cnt] = d->be_min_written; > + d->be_cnt += 1; > + } > + > + return ret; > +} > + > +static void char_mux_be_finalize(Object *obj) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(obj); > + CharBackend *fe = d->frontend; > + int i; > + > + if (fe) { > + fe->chr = NULL; > + } > + for (i = 0; i < d->be_cnt; i++) { > + qemu_chr_fe_deinit(&d->backends[i], false); > + } > +} > + > +static void mux_be_chr_update_read_handlers(Chardev *chr) > +{ > + MuxBeChardev *d = MUX_BE_CHARDEV(chr); > + int i; > + > + for (i = 0; i < d->be_cnt; i++) { > + /* Fix up the real driver with mux routines */ > + qemu_chr_fe_set_handlers_full(&d->backends[i], > + mux_be_chr_can_read, > + mux_be_chr_read, > + mux_be_chr_event, > + NULL, > + chr, > + chr->gcontext, true, false); > + } > +} > + > +bool mux_be_chr_attach_frontend(MuxBeChardev *d, CharBackend *b, Error > **errp) > +{ > + if (d->frontend) { > + error_setg(errp, > + "multiplexed chardev '%s' is already used " > + "for multiplexing", d->parent.label); > + return false; > + } > + d->frontend = b; > + > + return true; > +} > + > +void mux_be_chr_detach_frontend(MuxBeChardev *d) > +{ > + d->frontend = NULL; > +} > + > +static void qemu_chr_open_mux_be(Chardev *chr, > + ChardevBackend *backend, > + bool *be_opened, > + Error **errp) > +{ > + /* > + * Only default to opened state if we've realized the initial > + * set of muxes > + */ > + *be_opened = mux_is_opened(); > +} > + > +static void qemu_chr_parse_mux_be(QemuOpts *opts, ChardevBackend *backend, > + Error **errp) > +{ > + ChardevMuxBe *mux; > + > + backend->type = CHARDEV_BACKEND_KIND_MUX_BE; > + mux = backend->u.mux_be.data = g_new0(ChardevMuxBe, 1); > + qemu_chr_parse_common(opts, qapi_ChardevMuxBe_base(mux)); > +} > + > +static void char_mux_be_class_init(ObjectClass *oc, void *data) > +{ > + ChardevClass *cc = CHARDEV_CLASS(oc); > + > + cc->parse = qemu_chr_parse_mux_be; > + cc->open = qemu_chr_open_mux_be; > + cc->chr_write = mux_be_chr_write; > + cc->chr_add_watch = mux_be_chr_add_watch; > + cc->chr_be_event = mux_be_chr_be_event; > + cc->chr_update_read_handler = mux_be_chr_update_read_handlers; > +} > + > +static const TypeInfo char_mux_be_type_info = { > + .name = TYPE_CHARDEV_MUX_BE, > + .parent = TYPE_CHARDEV, > + .class_init = char_mux_be_class_init, > + .instance_size = sizeof(MuxBeChardev), > + .instance_finalize = char_mux_be_finalize, > +}; > + > +static void register_types(void) > +{ > + type_register_static(&char_mux_be_type_info); > +} > + > +type_init(register_types); > diff --git a/chardev/char.c b/chardev/char.c > index cffe60860589..58fa8ac70a1e 100644 > --- a/chardev/char.c > +++ b/chardev/char.c > @@ -341,6 +341,9 @@ static bool qemu_chr_is_busy(Chardev *s) > if (CHARDEV_IS_MUX_FE(s)) { > MuxFeChardev *d = MUX_FE_CHARDEV(s); > return d->mux_bitset != 0; > + } else if (CHARDEV_IS_MUX_BE(s)) { > + MuxBeChardev *d = MUX_BE_CHARDEV(s); > + return d->frontend != NULL; > } else { > return s->be != NULL; > } > @@ -648,7 +651,8 @@ static Chardev *__qemu_chr_new_from_opts(QemuOpts > *opts, GMainContext *context, > ChardevBackend *backend = NULL; > const char *name = qemu_opt_get(opts, "backend"); > const char *id = qemu_opts_id(opts); > - char *bid = NULL; > + const char *mux_be_id = NULL; > + char *mux_fe_id = NULL; > > if (name && is_help_option(name)) { > GString *str = g_string_new(""); > @@ -676,10 +680,16 @@ static Chardev *__qemu_chr_new_from_opts(QemuOpts > *opts, GMainContext *context, > } > > if (qemu_opt_get_bool(opts, "mux", 0)) { > - bid = g_strdup_printf("%s-base", id); > + mux_fe_id = g_strdup_printf("%s-base", id); > + } > + mux_be_id = qemu_opt_get(opts, "mux-be-id"); > + if (mux_be_id && mux_fe_id) { > + error_setg(errp, "chardev: mux and mux-be can't be used for the > same " > + "device"); > + goto out; > } > > - chr = qemu_chardev_new(bid ? bid : id, > + chr = qemu_chardev_new(mux_fe_id ? mux_fe_id : id, > object_class_get_name(OBJECT_CLASS(cc)), > backend, context, errp); > if (chr == NULL) { > @@ -687,25 +697,40 @@ static Chardev *__qemu_chr_new_from_opts(QemuOpts > *opts, GMainContext *context, > } > > base = chr; > - if (bid) { > + if (mux_fe_id) { > Chardev *mux; > qapi_free_ChardevBackend(backend); > backend = g_new0(ChardevBackend, 1); > backend->type = CHARDEV_BACKEND_KIND_MUX; > backend->u.mux.data = g_new0(ChardevMux, 1); > - backend->u.mux.data->chardev = g_strdup(bid); > + backend->u.mux.data->chardev = g_strdup(mux_fe_id); > mux = qemu_chardev_new(id, TYPE_CHARDEV_MUX_FE, backend, context, > errp); > if (mux == NULL) { > - object_unparent(OBJECT(chr)); > - chr = NULL; > - goto out; > + goto unparent_and_out; > } > chr = mux; > + } else if (mux_be_id) { > + Chardev *s; > + > + s = qemu_chr_find(mux_be_id); > + if (!s) { > + error_setg(errp, "chardev: mux-be device can't be found by id > '%s'", > + mux_be_id); > + goto unparent_and_out; > + } > + if (!CHARDEV_IS_MUX_BE(s)) { > + error_setg(errp, "chardev: device '%s' is not a multiplexer > device" > + " of 'mux-be' type", mux_be_id); > + goto unparent_and_out; > + } > + if (!mux_be_chr_attach_chardev(MUX_BE_CHARDEV(s), chr, errp)) { > + goto unparent_and_out; > + } > } > > out: > qapi_free_ChardevBackend(backend); > - g_free(bid); > + g_free(mux_fe_id); > > if (replay && base) { > /* RR should be set on the base device, not the mux */ > @@ -713,6 +738,11 @@ out: > } > > return chr; > + > +unparent_and_out: > + object_unparent(OBJECT(chr)); > + chr = NULL; > + goto out; > } > > Chardev *qemu_chr_new_from_opts(QemuOpts *opts, GMainContext *context, > @@ -1114,7 +1144,7 @@ ChardevReturn *qmp_chardev_change(const char *id, > ChardevBackend *backend, > return NULL; > } > > - if (CHARDEV_IS_MUX_FE(chr)) { > + if (CHARDEV_IS_MUX_FE(chr) || CHARDEV_IS_MUX_BE(chr)) { > error_setg(errp, "Mux device hotswap not supported yet"); > return NULL; > } > @@ -1302,7 +1332,7 @@ static int chardev_options_parsed_cb(Object *child, > void *opaque) > { > Chardev *chr = (Chardev *)child; > > - if (!chr->be_open && CHARDEV_IS_MUX_FE(chr)) { > + if (!chr->be_open && (CHARDEV_IS_MUX_FE(chr) || > CHARDEV_IS_MUX_BE(chr))) { > open_muxes(chr); > } > > @@ -1329,8 +1359,10 @@ void mux_chr_send_all_event(Chardev *chr, > QEMUChrEvent event) > > if (CHARDEV_IS_MUX_FE(chr)) { > MuxFeChardev *d = MUX_FE_CHARDEV(chr); > - > mux_fe_chr_send_all_event(d, event); > + } else if (CHARDEV_IS_MUX_BE(chr)) { > + MuxBeChardev *d = MUX_BE_CHARDEV(chr); > + mux_be_chr_send_all_event(d, event); > } > } > > diff --git a/chardev/chardev-internal.h b/chardev/chardev-internal.h > index 94c8d07ac235..8ea1258f8ff4 100644 > --- a/chardev/chardev-internal.h > +++ b/chardev/chardev-internal.h > @@ -35,7 +35,9 @@ > > struct MuxFeChardev { > Chardev parent; > + /* Linked frontends */ > CharBackend *backends[MAX_MUX]; > + /* Linked backend */ > CharBackend chr; > Maybe a patch to rename those fields would help. > > unsigned long mux_bitset; > int focus; > @@ -54,10 +56,36 @@ struct MuxFeChardev { > }; > typedef struct MuxFeChardev MuxFeChardev; > > +struct MuxBeChardev { > + Chardev parent; > + /* Linked frontend */ > + CharBackend *frontend; > + /* Linked backends */ > + CharBackend backends[MAX_MUX]; > + /* > + * Number of backends attached to this mux. Once attached, a > + * backend can't be detached, so the counter is only increasing. > + * To safely remove a backend, mux has to be removed first. > + */ > + unsigned int be_cnt; > + /* > + * Counters of written bytes from a single frontend device > + * to multiple backend devices. > + */ > + unsigned int be_written[MAX_MUX]; > + unsigned int be_min_written; > +}; > +typedef struct MuxBeChardev MuxBeChardev; > + > DECLARE_INSTANCE_CHECKER(MuxFeChardev, MUX_FE_CHARDEV, > TYPE_CHARDEV_MUX_FE) > -#define CHARDEV_IS_MUX_FE(chr) \ > +DECLARE_INSTANCE_CHECKER(MuxBeChardev, MUX_BE_CHARDEV, > + TYPE_CHARDEV_MUX_BE) > + > +#define CHARDEV_IS_MUX_FE(chr) \ > object_dynamic_cast(OBJECT(chr), TYPE_CHARDEV_MUX_FE) > +#define CHARDEV_IS_MUX_BE(chr) \ > + object_dynamic_cast(OBJECT(chr), TYPE_CHARDEV_MUX_BE) > > void mux_chr_send_all_event(Chardev *chr, QEMUChrEvent event); > > @@ -67,6 +95,10 @@ void mux_fe_chr_send_all_event(MuxFeChardev *d, > QEMUChrEvent event); > bool mux_fe_chr_attach_frontend(MuxFeChardev *d, CharBackend *b, > unsigned int *tag, Error **errp); > bool mux_fe_chr_detach_frontend(MuxFeChardev *d, unsigned int tag); > +void mux_be_chr_send_all_event(MuxBeChardev *d, QEMUChrEvent event); > +bool mux_be_chr_attach_chardev(MuxBeChardev *d, Chardev *chr, Error > **errp); > +bool mux_be_chr_attach_frontend(MuxBeChardev *d, CharBackend *b, Error > **errp); > +void mux_be_chr_detach_frontend(MuxBeChardev *d); > > Object *get_chardevs_root(void); > > diff --git a/chardev/meson.build b/chardev/meson.build > index 778444a00ca6..3a9f5565372b 100644 > --- a/chardev/meson.build > +++ b/chardev/meson.build > @@ -3,6 +3,7 @@ chardev_ss.add(files( > 'char-file.c', > 'char-io.c', > 'char-mux-fe.c', > + 'char-mux-be.c', > 'char-null.c', > 'char-pipe.c', > 'char-ringbuf.c', > diff --git a/include/chardev/char.h b/include/chardev/char.h > index 0bec974f9d73..c58c11c4eeaf 100644 > --- a/include/chardev/char.h > +++ b/include/chardev/char.h > @@ -232,6 +232,7 @@ OBJECT_DECLARE_TYPE(Chardev, ChardevClass, CHARDEV) > > #define TYPE_CHARDEV_NULL "chardev-null" > #define TYPE_CHARDEV_MUX_FE "chardev-mux" > +#define TYPE_CHARDEV_MUX_BE "chardev-mux-be" > #define TYPE_CHARDEV_RINGBUF "chardev-ringbuf" > #define TYPE_CHARDEV_PTY "chardev-pty" > #define TYPE_CHARDEV_CONSOLE "chardev-console" > diff --git a/qapi/char.json b/qapi/char.json > index fb0dedb24383..cdec8f9cf4e2 100644 > --- a/qapi/char.json > +++ b/qapi/char.json > @@ -336,6 +336,17 @@ > 'data': { 'chardev': 'str' }, > 'base': 'ChardevCommon' } > > +## > +# @ChardevMuxBe: > +# > +# Configuration info for mux-be chardevs. > +# > +# Since: 9.2 > +## > +{ 'struct': 'ChardevMuxBe', > + 'data': { }, > + 'base': 'ChardevCommon' } > + > ## > # @ChardevStdio: > # > @@ -483,6 +494,8 @@ > # > # @mux: (since 1.5) > # > +# @mux-be: (since 9.2) > +# > # @msmouse: emulated Microsoft serial mouse (since 1.5) > # > # @wctablet: emulated Wacom Penpartner serial tablet (since 2.9) > @@ -525,6 +538,7 @@ > 'pty', > 'null', > 'mux', > + 'mux-be', > 'msmouse', > 'wctablet', > { 'name': 'braille', 'if': 'CONFIG_BRLAPI' }, > @@ -599,6 +613,16 @@ > { 'struct': 'ChardevMuxWrapper', > 'data': { 'data': 'ChardevMux' } } > > +## > +# @ChardevMuxBeWrapper: > +# > +# @data: Configuration info for mux-be chardevs > +# > +# Since: 9.2 > +## > +{ 'struct': 'ChardevMuxBeWrapper', > + 'data': { 'data': 'ChardevMuxBe' } } > + > ## > # @ChardevStdioWrapper: > # > @@ -707,6 +731,7 @@ > 'pty': 'ChardevPtyWrapper', > 'null': 'ChardevCommonWrapper', > 'mux': 'ChardevMuxWrapper', > + 'mux-be': 'ChardevMuxBeWrapper', > 'msmouse': 'ChardevCommonWrapper', > 'wctablet': 'ChardevCommonWrapper', > 'braille': { 'type': 'ChardevCommonWrapper', > -- > 2.34.1 > > > -- Marc-André Lureau
Hi, On Wed, Oct 16, 2024 at 1:14 PM Marc-André Lureau <marcandre.lureau@gmail.com> wrote: > > Hi > > On Wed, Oct 16, 2024 at 2:29 PM Roman Penyaev <r.peniaev@gmail.com> wrote: >> >> This patch implements multiplexing capability of several backend >> devices, which opens up an opportunity to use a single frontend >> device on the guest, which can be manipulated from several >> backend devices. >> >> The idea of the change is trivial: keep list of backend devices >> (up to 4), init them on demand and forward data buffer back and >> forth. >> >> Patch implements another multiplexer type `mux-be`. The following >> is QEMU command line example: >> >> -chardev mux-be,id=mux0 \ >> -chardev socket,path=/tmp/sock,server=on,wait=off,id=sock0,mux-be-id=mux0 \ >> -chardev vc,id=vc0,mux-be-id=mux0 \ > > > I am not sure about adding "mux-be-id" to all chardev. It avoids the issue of expressing a list of ids in mux-be though (while it may have potential loop!) Loop is a good point, but actually can be easily fixed by forbidding the use of stacked muxes and a reference on itself. Do you think that would be enough? -- Roman
Hi On Wed, Oct 16, 2024 at 3:13 PM Marc-André Lureau < marcandre.lureau@gmail.com> wrote: > Hi > > On Wed, Oct 16, 2024 at 2:29 PM Roman Penyaev <r.peniaev@gmail.com> wrote: > >> This patch implements multiplexing capability of several backend >> devices, which opens up an opportunity to use a single frontend >> device on the guest, which can be manipulated from several >> backend devices. >> >> The idea of the change is trivial: keep list of backend devices >> (up to 4), init them on demand and forward data buffer back and >> forth. >> >> Patch implements another multiplexer type `mux-be`. The following >> is QEMU command line example: >> >> -chardev mux-be,id=mux0 \ >> -chardev >> socket,path=/tmp/sock,server=on,wait=off,id=sock0,mux-be-id=mux0 \ >> -chardev vc,id=vc0,mux-be-id=mux0 \ >> > > I am not sure about adding "mux-be-id" to all chardev. It avoids the issue > of expressing a list of ids in mux-be though (while it may have potential > loop!) > > (well, the loop can be expressed with an array list as well, and deepen.. I don't think we have enough sanity check around that, especially at run time). -- Marc-André Lureau
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