We'll need a possibility to postpone connect step to later point in
time to implement backend-transfer migration feature for vhost-user-blk
in further commits. Let's start with new char interface for backends.
.init() takes QAPI parameters and should parse them, called early
.connect() should actually establish a connection, and postponed to
the point of attaching to frontend. Called at later point, either
at time of attaching frontend, either from qemu_chr_wait_connected().
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
chardev/char-fe.c | 4 ++++
chardev/char.c | 40 +++++++++++++++++++++++++++++++++++++---
include/chardev/char.h | 22 +++++++++++++++++++++-
3 files changed, 62 insertions(+), 4 deletions(-)
diff --git a/chardev/char-fe.c b/chardev/char-fe.c
index 158a5f4f55..973fed5bea 100644
--- a/chardev/char-fe.c
+++ b/chardev/char-fe.c
@@ -193,6 +193,10 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
{
unsigned int tag = 0;
+ if (!qemu_chr_connect(s, errp)) {
+ return false;
+ }
+
if (s) {
if (CHARDEV_IS_MUX(s)) {
MuxChardev *d = MUX_CHARDEV(s);
diff --git a/chardev/char.c b/chardev/char.c
index 6498d53daa..01ffe37acf 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -33,6 +33,7 @@
#include "qapi/error.h"
#include "qapi/qapi-commands-char.h"
#include "qapi/qmp/qerror.h"
+#include "qom/object.h"
#include "system/replay.h"
#include "qemu/help_option.h"
#include "qemu/module.h"
@@ -338,10 +339,29 @@ static bool qemu_chr_is_busy(Chardev *s)
}
}
+bool qemu_chr_connect(Chardev *chr, Error **errp)
+{
+ ChardevClass *cc = CHARDEV_GET_CLASS(chr);
+
+ if (chr->connect_postponed) {
+ assert(cc->connect);
+ chr->connect_postponed = false;
+ if (!cc->connect(chr, errp)) {
+ return false;
+ }
+ }
+
+ return true;
+}
+
int qemu_chr_wait_connected(Chardev *chr, Error **errp)
{
ChardevClass *cc = CHARDEV_GET_CLASS(chr);
+ if (!qemu_chr_connect(chr, errp)) {
+ return -1;
+ }
+
if (cc->chr_wait_connected) {
return cc->chr_wait_connected(chr, errp);
}
@@ -1029,7 +1049,7 @@ static Chardev *chardev_new(const char *id, const char *typename,
{
Object *obj;
Chardev *chr = NULL;
- Error *local_err = NULL;
+ ChardevClass *cc;
assert(g_str_has_prefix(typename, "chardev-"));
assert(id);
@@ -1044,8 +1064,22 @@ static Chardev *chardev_new(const char *id, const char *typename,
goto fail;
}
- if (!qemu_char_open(chr, backend, typename + 8, &local_err)) {
- goto fail;
+ cc = CHARDEV_GET_CLASS(chr);
+
+ if (cc->init) {
+ assert(!cc->open);
+ assert(cc->connect);
+
+ if (!cc->init(chr, backend, errp)) {
+ goto fail;
+ }
+ assert(chr->filename);
+
+ chr->connect_postponed = true;
+ } else {
+ if (!qemu_char_open(chr, backend, typename + 8, errp)) {
+ goto fail;
+ }
}
return chr;
diff --git a/include/chardev/char.h b/include/chardev/char.h
index 429852f8d9..ebadaf3482 100644
--- a/include/chardev/char.h
+++ b/include/chardev/char.h
@@ -63,6 +63,7 @@ struct Chardev {
CharBackend *be;
char *label;
char *filename;
+ bool connect_postponed;
int logfd;
int be_open;
/* used to coordinate the chardev-change special-case: */
@@ -225,6 +226,7 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename,
bool permit_mux_mon);
int qemu_chr_write(Chardev *s, const uint8_t *buf, int len, bool write_all);
#define qemu_chr_write_all(s, buf, len) qemu_chr_write(s, buf, len, true)
+bool qemu_chr_connect(Chardev *chr, Error **errp);
int qemu_chr_wait_connected(Chardev *chr, Error **errp);
#define TYPE_CHARDEV "chardev"
@@ -259,10 +261,28 @@ struct ChardevClass {
/* parse command line options and populate QAPI @backend */
void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp);
- /* called after construction, open/starts the backend */
+ /*
+ * Called after construction, create and open/starts the backend,
+ * mutual exclusive with .init. .connect must not be defined when
+ * .open is defined.
+ */
void (*open)(Chardev *chr, ChardevBackend *backend,
bool *be_opened, Error **errp);
+ /*
+ * Called after construction, create the backend, mutual exclusive
+ * with .open, and must be accompanied by .connect.
+ * Must set chr-filename.
+ */
+ bool (*init)(Chardev *chr, ChardevBackend *backend,
+ Error **errp);
+
+ /*
+ * Called after .init(), open/starts the backend, mutual exclusive
+ * with .open. Must send CHR_EVENT_OPENED.
+ */
+ bool (*connect)(Chardev *chr, Error **errp);
+
/* write buf to the backend */
int (*chr_write)(Chardev *s, const uint8_t *buf, int len);
--
2.48.1On Mon, Oct 13, 2025 at 5:40 PM Vladimir Sementsov-Ogievskiy
<vsementsov@yandex-team.ru> wrote:
>
> We'll need a possibility to postpone connect step to later point in
> time to implement backend-transfer migration feature for vhost-user-blk
> in further commits. Let's start with new char interface for backends.
>
> .init() takes QAPI parameters and should parse them, called early
>
> .connect() should actually establish a connection, and postponed to
> the point of attaching to frontend. Called at later point, either
> at time of attaching frontend, either from qemu_chr_wait_connected().
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
> ---
> chardev/char-fe.c | 4 ++++
> chardev/char.c | 40 +++++++++++++++++++++++++++++++++++++---
> include/chardev/char.h | 22 +++++++++++++++++++++-
> 3 files changed, 62 insertions(+), 4 deletions(-)
>
> diff --git a/chardev/char-fe.c b/chardev/char-fe.c
> index 158a5f4f55..973fed5bea 100644
> --- a/chardev/char-fe.c
> +++ b/chardev/char-fe.c
> @@ -193,6 +193,10 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
> {
> unsigned int tag = 0;
>
> + if (!qemu_chr_connect(s, errp)) {
> + return false;
> + }
> +
> if (s) {
> if (CHARDEV_IS_MUX(s)) {
> MuxChardev *d = MUX_CHARDEV(s);
> diff --git a/chardev/char.c b/chardev/char.c
> index 6498d53daa..01ffe37acf 100644
> --- a/chardev/char.c
> +++ b/chardev/char.c
> @@ -33,6 +33,7 @@
> #include "qapi/error.h"
> #include "qapi/qapi-commands-char.h"
> #include "qapi/qmp/qerror.h"
> +#include "qom/object.h"
> #include "system/replay.h"
> #include "qemu/help_option.h"
> #include "qemu/module.h"
> @@ -338,10 +339,29 @@ static bool qemu_chr_is_busy(Chardev *s)
> }
> }
>
> +bool qemu_chr_connect(Chardev *chr, Error **errp)
> +{
> + ChardevClass *cc = CHARDEV_GET_CLASS(chr);
> +
> + if (chr->connect_postponed) {
> + assert(cc->connect);
> + chr->connect_postponed = false;
> + if (!cc->connect(chr, errp)) {
> + return false;
> + }
> + }
> +
> + return true;
> +}
> +
> int qemu_chr_wait_connected(Chardev *chr, Error **errp)
> {
> ChardevClass *cc = CHARDEV_GET_CLASS(chr);
>
> + if (!qemu_chr_connect(chr, errp)) {
> + return -1;
> + }
> +
> if (cc->chr_wait_connected) {
> return cc->chr_wait_connected(chr, errp);
> }
> @@ -1029,7 +1049,7 @@ static Chardev *chardev_new(const char *id, const char *typename,
> {
> Object *obj;
> Chardev *chr = NULL;
> - Error *local_err = NULL;
> + ChardevClass *cc;
>
> assert(g_str_has_prefix(typename, "chardev-"));
> assert(id);
> @@ -1044,8 +1064,22 @@ static Chardev *chardev_new(const char *id, const char *typename,
> goto fail;
> }
>
> - if (!qemu_char_open(chr, backend, typename + 8, &local_err)) {
> - goto fail;
> + cc = CHARDEV_GET_CLASS(chr);
> +
> + if (cc->init) {
> + assert(!cc->open);
> + assert(cc->connect);
> +
> + if (!cc->init(chr, backend, errp)) {
> + goto fail;
> + }
> + assert(chr->filename);
> +
> + chr->connect_postponed = true;
> + } else {
> + if (!qemu_char_open(chr, backend, typename + 8, errp)) {
> + goto fail;
> + }
> }
>
> return chr;
> diff --git a/include/chardev/char.h b/include/chardev/char.h
> index 429852f8d9..ebadaf3482 100644
> --- a/include/chardev/char.h
> +++ b/include/chardev/char.h
> @@ -63,6 +63,7 @@ struct Chardev {
> CharBackend *be;
> char *label;
> char *filename;
> + bool connect_postponed;
> int logfd;
> int be_open;
> /* used to coordinate the chardev-change special-case: */
> @@ -225,6 +226,7 @@ QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename,
> bool permit_mux_mon);
> int qemu_chr_write(Chardev *s, const uint8_t *buf, int len, bool write_all);
> #define qemu_chr_write_all(s, buf, len) qemu_chr_write(s, buf, len, true)
> +bool qemu_chr_connect(Chardev *chr, Error **errp);
> int qemu_chr_wait_connected(Chardev *chr, Error **errp);
>
> #define TYPE_CHARDEV "chardev"
> @@ -259,10 +261,28 @@ struct ChardevClass {
> /* parse command line options and populate QAPI @backend */
> void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp);
>
> - /* called after construction, open/starts the backend */
> + /*
> + * Called after construction, create and open/starts the backend,
> + * mutual exclusive with .init. .connect must not be defined when
> + * .open is defined.
> + */
> void (*open)(Chardev *chr, ChardevBackend *backend,
> bool *be_opened, Error **errp);
>
> + /*
> + * Called after construction, create the backend, mutual exclusive
> + * with .open, and must be accompanied by .connect.
> + * Must set chr-filename.
> + */
> + bool (*init)(Chardev *chr, ChardevBackend *backend,
> + Error **errp);
> +
> + /*
> + * Called after .init(), open/starts the backend, mutual exclusive
> + * with .open. Must send CHR_EVENT_OPENED.
> + */
> + bool (*connect)(Chardev *chr, Error **errp);
> +
> /* write buf to the backend */
> int (*chr_write)(Chardev *s, const uint8_t *buf, int len);
>
> --
> 2.48.1
>
>
--
Marc-André Lureau
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