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From: marcandre.lureau@redhat.com
To: qemu-devel@nongnu.org
Cc: Eric Blake <eblake@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>,
Mahmoud Mandour <ma.mandourr@gmail.com>,
Markus Armbruster <armbru@redhat.com>, peter.maydell@linaro.org,
Gerd Hoffmann <kraxel@redhat.com>, Alexandre Iooss <erdnaxe@crans.org>,
=?UTF-8?q?Alex=20Benn=C3=A9e?= <alex.bennee@linaro.org>,
Pierrick Bouvier <pierrick.bouvier@linaro.org>,
=?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= <marcandre.lureau@redhat.com>,
Roman Penyaev <r.peniaev@gmail.com>
Subject: [PULL 2/8] chardev/char-hub: implement backend chardev aggregator
Date: Mon, 3 Feb 2025 16:57:14 +0400
Message-ID: <20250203125721.640451-3-marcandre.lureau@redhat.com>
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From: Roman Penyaev <r.peniaev@gmail.com>
This patch implements a new chardev backend `hub` device, which
aggregates input from multiple backend devices and forwards it to a
single frontend device. Additionally, `hub` device takes the output
from the frontend device and sends it back to all the connected
backend devices. This allows for seamless interaction between
different backend devices and a single frontend interface.
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.
The following is QEMU command line example:
-chardev pty,path=3D/tmp/pty,id=3Dpty0 \
-chardev vc,id=3Dvc0 \
-chardev hub,id=3Dhub0,chardevs.0=3Dpty0,chardevs.1=3Dvc0 \
-device virtconsole,chardev=3Dhub0 \
-vnc 0.0.0.0:0
Which creates 2 backend devices: text virtual console (`vc0`) and a
pseudo TTY (`pty0`) connected to the single virtio hvc console with
the backend aggregator (`hub0`) help. `vc0` renders text to an image,
which can be shared over the VNC protocol. `pty0` is a pseudo TTY
backend which provides biderectional communication to the virtio hvc
console.
'chardevs.N' list syntax is used for the sake of compatibility with
the representation of JSON lists in 'key=3Dval' pairs format of the
util/keyval.c, despite the fact that modern QAPI way of parsing,
namely qobject_input_visitor_new_str(), is not used. Choice of keeping
QAPI list syntax may help to smoothly switch to modern parsing in the
future.
Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Reviewed-by: "Marc-Andr=C3=A9 Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Message-ID: <20250123085327.965501-3-r.peniaev@gmail.com>
---
qapi/char.json | 27 ++++
chardev/chardev-internal.h | 51 ++++++-
include/chardev/char.h | 1 +
chardev/char-hub.c | 301 +++++++++++++++++++++++++++++++++++++
chardev/char.c | 23 ++-
chardev/meson.build | 1 +
6 files changed, 401 insertions(+), 3 deletions(-)
create mode 100644 chardev/char-hub.c
diff --git a/qapi/char.json b/qapi/char.json
index e045354350..f02b66c06b 100644
--- a/qapi/char.json
+++ b/qapi/char.json
@@ -332,6 +332,19 @@
'data': { 'chardev': 'str' },
'base': 'ChardevCommon' }
=20
+##
+# @ChardevHub:
+#
+# Configuration info for hub chardevs.
+#
+# @chardevs: List of chardev IDs, which should be added to this hub
+#
+# Since: 10.0
+##
+{ 'struct': 'ChardevHub',
+ 'data': { 'chardevs': ['str'] },
+ 'base': 'ChardevCommon' }
+
##
# @ChardevStdio:
#
@@ -479,6 +492,8 @@
#
# @mux: (since 1.5)
#
+# @hub: (since 10.0)
+#
# @msmouse: emulated Microsoft serial mouse (since 1.5)
#
# @wctablet: emulated Wacom Penpartner serial tablet (since 2.9)
@@ -521,6 +536,7 @@
'pty',
'null',
'mux',
+ 'hub',
'msmouse',
'wctablet',
{ 'name': 'braille', 'if': 'CONFIG_BRLAPI' },
@@ -595,6 +611,16 @@
{ 'struct': 'ChardevMuxWrapper',
'data': { 'data': 'ChardevMux' } }
=20
+##
+# @ChardevHubWrapper:
+#
+# @data: Configuration info for hub chardevs
+#
+# Since: 10.0
+##
+{ 'struct': 'ChardevHubWrapper',
+ 'data': { 'data': 'ChardevHub' } }
+
##
# @ChardevStdioWrapper:
#
@@ -703,6 +729,7 @@
'pty': 'ChardevPtyWrapper',
'null': 'ChardevCommonWrapper',
'mux': 'ChardevMuxWrapper',
+ 'hub': 'ChardevHubWrapper',
'msmouse': 'ChardevCommonWrapper',
'wctablet': 'ChardevCommonWrapper',
'braille': { 'type': 'ChardevCommonWrapper',
diff --git a/chardev/chardev-internal.h b/chardev/chardev-internal.h
index 853807f3cb..9752dd75f7 100644
--- a/chardev/chardev-internal.h
+++ b/chardev/chardev-internal.h
@@ -29,13 +29,16 @@
#include "chardev/char-fe.h"
#include "qom/object.h"
=20
+#define MAX_HUB 4
#define MAX_MUX 4
#define MUX_BUFFER_SIZE 32 /* Must be a power of 2. */
#define MUX_BUFFER_MASK (MUX_BUFFER_SIZE - 1)
=20
struct MuxChardev {
Chardev parent;
+ /* Linked frontends */
CharBackend *backends[MAX_MUX];
+ /* Linked backend */
CharBackend chr;
unsigned long mux_bitset;
int focus;
@@ -53,11 +56,57 @@ struct MuxChardev {
int64_t timestamps_start;
};
typedef struct MuxChardev MuxChardev;
+typedef struct HubChardev HubChardev;
+typedef struct HubCharBackend HubCharBackend;
+
+/*
+ * Back-pointer on a hub, actual backend and its index in
+ * `hub->backends` array
+ */
+struct HubCharBackend {
+ HubChardev *hub;
+ CharBackend be;
+ unsigned int be_ind;
+};
+
+struct HubChardev {
+ Chardev parent;
+ /* Linked backends */
+ HubCharBackend backends[MAX_HUB];
+ /*
+ * Number of backends attached to this hub. Once attached, a
+ * backend can't be detached, so the counter is only increasing.
+ * To safely remove a backend, hub has to be removed first.
+ */
+ unsigned int be_cnt;
+ /*
+ * Number of CHR_EVEN_OPENED events from all backends. Needed to
+ * send CHR_EVEN_CLOSED only when counter goes to zero.
+ */
+ unsigned int be_event_opened_cnt;
+ /*
+ * Counters of written bytes from a single frontend device
+ * to multiple backend devices.
+ */
+ unsigned int be_written[MAX_HUB];
+ unsigned int be_min_written;
+ /*
+ * Index of a backend device which got EAGAIN on last write,
+ * -1 is invalid index.
+ */
+ int be_eagain_ind;
+};
+typedef struct HubChardev HubChardev;
=20
DECLARE_INSTANCE_CHECKER(MuxChardev, MUX_CHARDEV,
TYPE_CHARDEV_MUX)
-#define CHARDEV_IS_MUX(chr) \
+DECLARE_INSTANCE_CHECKER(HubChardev, HUB_CHARDEV,
+ TYPE_CHARDEV_HUB)
+
+#define CHARDEV_IS_MUX(chr) \
object_dynamic_cast(OBJECT(chr), TYPE_CHARDEV_MUX)
+#define CHARDEV_IS_HUB(chr) \
+ object_dynamic_cast(OBJECT(chr), TYPE_CHARDEV_HUB)
=20
bool mux_chr_attach_frontend(MuxChardev *d, CharBackend *b,
unsigned int *tag, Error **errp);
diff --git a/include/chardev/char.h b/include/chardev/char.h
index 01df55f9e8..429852f8d9 100644
--- a/include/chardev/char.h
+++ b/include/chardev/char.h
@@ -232,6 +232,7 @@ OBJECT_DECLARE_TYPE(Chardev, ChardevClass, CHARDEV)
=20
#define TYPE_CHARDEV_NULL "chardev-null"
#define TYPE_CHARDEV_MUX "chardev-mux"
+#define TYPE_CHARDEV_HUB "chardev-hub"
#define TYPE_CHARDEV_RINGBUF "chardev-ringbuf"
#define TYPE_CHARDEV_PTY "chardev-pty"
#define TYPE_CHARDEV_CONSOLE "chardev-console"
diff --git a/chardev/char-hub.c b/chardev/char-hub.c
new file mode 100644
index 0000000000..3a4aae3289
--- /dev/null
+++ b/chardev/char-hub.c
@@ -0,0 +1,301 @@
+/*
+ * QEMU Character Hub Device
+ *
+ * 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"), t=
o deal
+ * in the Software without restriction, including without limitation the r=
ights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or se=
ll
+ * 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 OT=
HER
+ * 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/option.h"
+#include "chardev/char.h"
+#include "chardev-internal.h"
+
+/*
+ * Character hub device aggregates input from multiple backend devices
+ * and forwards it to a single frontend device. Additionally, hub
+ * device takes the output from the frontend device and sends it back
+ * to all the connected 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.
+ * Called with chr_write_lock held.
+ */
+static int hub_chr_write(Chardev *chr, const uint8_t *buf, int len)
+{
+ HubChardev *d =3D HUB_CHARDEV(chr);
+ int r, i, ret =3D len;
+ unsigned int written;
+
+ /* Invalidate index on every write */
+ d->be_eagain_ind =3D -1;
+
+ for (i =3D 0; i < d->be_cnt; i++) {
+ if (!d->backends[i].be.chr->be_open) {
+ /* Skip closed backend */
+ continue;
+ }
+ written =3D d->be_written[i] - d->be_min_written;
+ if (written) {
+ /* Written in the previous call so take into account */
+ ret =3D MIN(written, ret);
+ continue;
+ }
+ r =3D qemu_chr_fe_write(&d->backends[i].be, buf, len);
+ if (r < 0) {
+ if (errno =3D=3D EAGAIN) {
+ /* Set index and expect to be called soon on watch wake up=
*/
+ d->be_eagain_ind =3D i;
+ }
+ return r;
+ }
+ d->be_written[i] +=3D r;
+ ret =3D MIN(r, ret);
+ }
+ d->be_min_written +=3D ret;
+
+
+ return ret;
+}
+
+static int hub_chr_can_read(void *opaque)
+{
+ HubCharBackend *backend =3D opaque;
+ CharBackend *fe =3D backend->hub->parent.be;
+
+ if (fe && fe->chr_can_read) {
+ return fe->chr_can_read(fe->opaque);
+ }
+
+ return 0;
+}
+
+static void hub_chr_read(void *opaque, const uint8_t *buf, int size)
+{
+ HubCharBackend *backend =3D opaque;
+ CharBackend *fe =3D backend->hub->parent.be;
+
+ if (fe && fe->chr_read) {
+ fe->chr_read(fe->opaque, buf, size);
+ }
+}
+
+static void hub_chr_event(void *opaque, QEMUChrEvent event)
+{
+ HubCharBackend *backend =3D opaque;
+ HubChardev *d =3D backend->hub;
+ CharBackend *fe =3D d->parent.be;
+
+ if (event =3D=3D CHR_EVENT_OPENED) {
+ /*
+ * Catch up with what was already written while this backend
+ * was closed
+ */
+ d->be_written[backend->be_ind] =3D d->be_min_written;
+
+ if (d->be_event_opened_cnt++) {
+ /* Ignore subsequent open events from other backends */
+ return;
+ }
+ } else if (event =3D=3D CHR_EVENT_CLOSED) {
+ if (!d->be_event_opened_cnt) {
+ /* Don't go below zero. Probably assert is better */
+ return;
+ }
+ if (--d->be_event_opened_cnt) {
+ /* Serve only the last one close event */
+ return;
+ }
+ }
+
+ if (fe && fe->chr_event) {
+ fe->chr_event(fe->opaque, event);
+ }
+}
+
+static GSource *hub_chr_add_watch(Chardev *s, GIOCondition cond)
+{
+ HubChardev *d =3D HUB_CHARDEV(s);
+ Chardev *chr;
+ ChardevClass *cc;
+
+ if (d->be_eagain_ind =3D=3D -1) {
+ return NULL;
+ }
+
+ assert(d->be_eagain_ind < d->be_cnt);
+ chr =3D qemu_chr_fe_get_driver(&d->backends[d->be_eagain_ind].be);
+ cc =3D CHARDEV_GET_CLASS(chr);
+ if (!cc->chr_add_watch) {
+ return NULL;
+ }
+
+ return cc->chr_add_watch(chr, cond);
+}
+
+static bool hub_chr_attach_chardev(HubChardev *d, Chardev *chr,
+ Error **errp)
+{
+ bool ret;
+
+ if (d->be_cnt >=3D MAX_HUB) {
+ error_setg(errp, "hub: too many uses of chardevs '%s'"
+ " (maximum is " stringify(MAX_HUB) ")",
+ d->parent.label);
+ return false;
+ }
+ ret =3D qemu_chr_fe_init(&d->backends[d->be_cnt].be, chr, errp);
+ if (ret) {
+ d->backends[d->be_cnt].hub =3D d;
+ d->backends[d->be_cnt].be_ind =3D d->be_cnt;
+ d->be_cnt +=3D 1;
+ }
+
+ return ret;
+}
+
+static void char_hub_finalize(Object *obj)
+{
+ HubChardev *d =3D HUB_CHARDEV(obj);
+ int i;
+
+ for (i =3D 0; i < d->be_cnt; i++) {
+ qemu_chr_fe_deinit(&d->backends[i].be, false);
+ }
+}
+
+static void hub_chr_update_read_handlers(Chardev *chr)
+{
+ HubChardev *d =3D HUB_CHARDEV(chr);
+ int i;
+
+ for (i =3D 0; i < d->be_cnt; i++) {
+ qemu_chr_fe_set_handlers_full(&d->backends[i].be,
+ hub_chr_can_read,
+ hub_chr_read,
+ hub_chr_event,
+ NULL,
+ &d->backends[i],
+ chr->gcontext, true, false);
+ }
+}
+
+static void qemu_chr_open_hub(Chardev *chr,
+ ChardevBackend *backend,
+ bool *be_opened,
+ Error **errp)
+{
+ ChardevHub *hub =3D backend->u.hub.data;
+ HubChardev *d =3D HUB_CHARDEV(chr);
+ strList *list =3D hub->chardevs;
+
+ d->be_eagain_ind =3D -1;
+
+ if (list =3D=3D NULL) {
+ error_setg(errp, "hub: 'chardevs' list is not defined");
+ return;
+ }
+
+ while (list) {
+ Chardev *s;
+
+ s =3D qemu_chr_find(list->value);
+ if (s =3D=3D NULL) {
+ error_setg(errp, "hub: chardev can't be found by id '%s'",
+ list->value);
+ return;
+ }
+ if (CHARDEV_IS_HUB(s) || CHARDEV_IS_MUX(s)) {
+ error_setg(errp, "hub: multiplexers and hub devices can't be "
+ "stacked, check chardev '%s', chardev should not "
+ "be a hub device or have 'mux=3Don' enabled",
+ list->value);
+ return;
+ }
+ if (!hub_chr_attach_chardev(d, s, errp)) {
+ return;
+ }
+ list =3D list->next;
+ }
+
+ /* Closed until an explicit event from backend */
+ *be_opened =3D false;
+}
+
+static void qemu_chr_parse_hub(QemuOpts *opts, ChardevBackend *backend,
+ Error **errp)
+{
+ ChardevHub *hub;
+ strList **tail;
+ int i;
+
+ backend->type =3D CHARDEV_BACKEND_KIND_HUB;
+ hub =3D backend->u.hub.data =3D g_new0(ChardevHub, 1);
+ qemu_chr_parse_common(opts, qapi_ChardevHub_base(hub));
+
+ tail =3D &hub->chardevs;
+
+ for (i =3D 0; i < MAX_HUB; i++) {
+ char optbuf[16];
+ const char *dev;
+
+ snprintf(optbuf, sizeof(optbuf), "chardevs.%u", i);
+ dev =3D qemu_opt_get(opts, optbuf);
+ if (!dev) {
+ break;
+ }
+
+ QAPI_LIST_APPEND(tail, g_strdup(dev));
+ }
+}
+
+static void char_hub_class_init(ObjectClass *oc, void *data)
+{
+ ChardevClass *cc =3D CHARDEV_CLASS(oc);
+
+ cc->parse =3D qemu_chr_parse_hub;
+ cc->open =3D qemu_chr_open_hub;
+ cc->chr_write =3D hub_chr_write;
+ cc->chr_add_watch =3D hub_chr_add_watch;
+ /* We handle events from backends only */
+ cc->chr_be_event =3D NULL;
+ cc->chr_update_read_handler =3D hub_chr_update_read_handlers;
+}
+
+static const TypeInfo char_hub_type_info =3D {
+ .name =3D TYPE_CHARDEV_HUB,
+ .parent =3D TYPE_CHARDEV,
+ .class_init =3D char_hub_class_init,
+ .instance_size =3D sizeof(HubChardev),
+ .instance_finalize =3D char_hub_finalize,
+};
+
+static void register_types(void)
+{
+ type_register_static(&char_hub_type_info);
+}
+
+type_init(register_types);
diff --git a/chardev/char.c b/chardev/char.c
index 7705da5ad0..5a9e9762ad 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -943,7 +943,26 @@ QemuOptsList qemu_chardev_opts =3D {
},{
.name =3D "chardev",
.type =3D QEMU_OPT_STRING,
+ },
+ /*
+ * Multiplexer options. Follows QAPI array syntax.
+ * See MAX_HUB macro to obtain array capacity.
+ */
+ {
+ .name =3D "chardevs.0",
+ .type =3D QEMU_OPT_STRING,
+ },{
+ .name =3D "chardevs.1",
+ .type =3D QEMU_OPT_STRING,
},{
+ .name =3D "chardevs.2",
+ .type =3D QEMU_OPT_STRING,
+ },{
+ .name =3D "chardevs.3",
+ .type =3D QEMU_OPT_STRING,
+ },
+
+ {
.name =3D "append",
.type =3D QEMU_OPT_BOOL,
},{
@@ -1106,8 +1125,8 @@ ChardevReturn *qmp_chardev_change(const char *id, Cha=
rdevBackend *backend,
return NULL;
}
=20
- if (CHARDEV_IS_MUX(chr)) {
- error_setg(errp, "Mux device hotswap not supported yet");
+ if (CHARDEV_IS_MUX(chr) || CHARDEV_IS_HUB(chr)) {
+ error_setg(errp, "For mux or hub device hotswap is not supported y=
et");
return NULL;
}
=20
diff --git a/chardev/meson.build b/chardev/meson.build
index 70070a8279..56ee39ac0b 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.c',
+ 'char-hub.c',
'char-null.c',
'char-pipe.c',
'char-ringbuf.c',
--=20
2.47.0