Hi
On Mon, Oct 13, 2025 at 5:39 PM Vladimir Sementsov-Ogievskiy
<[email protected]> wrote:
>
> Give vhost-user-blk a possibility (and responsibility) to decide when
> do connect. It will help us to realize vhost-user-blk backend-transfer
> migration feature:
>
> For incoming migration we'll need to postpone connect at least until
> early stage of migrate-incoming command, when we already know all
> migration parameters and can decide, are we going to do incoming
> backend-transfer (and get chardev fd from incoming stream), or we
> finally need to connect.
>
> With this patch, we don't modify vhost-user-blk.c: it already
> do call qemu_chr_fe_wait_connected(), which in turn calls
> qemu_chr_connect().
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
> ---
> chardev/char-fe.c | 21 +++++++++++++++++----
> hw/core/qdev-properties-system.c | 2 +-
> include/chardev/char-fe.h | 2 ++
> 3 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/chardev/char-fe.c b/chardev/char-fe.c
> index 973fed5bea..9e2c658cb9 100644
> --- a/chardev/char-fe.c
> +++ b/chardev/char-fe.c
> @@ -189,12 +189,20 @@ bool qemu_chr_fe_backend_open(CharBackend *be)
> return be->chr && be->chr->be_open;
> }
>
> -bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
> +bool qemu_chr_fe_init_ex(CharBackend *b, Chardev *s, ObjectClass *oc,
> + Error **errp)
> {
> unsigned int tag = 0;
> -
> - if (!qemu_chr_connect(s, errp)) {
> - return false;
> + const char *driver = oc ? object_class_get_name(oc) : NULL;
> +
> + /*
> + * vhost-user-blk wants call qemu_chr_connect by hand,
> + * to support backend-transfer migration feature.
> + */
> + if (!driver || !g_str_has_prefix(driver, "vhost-user-blk")) {
> + if (!qemu_chr_connect(s, errp)) {
> + return false;
> + }
Why not pass a bool "connect" instead?
DEFINE_PROP_CHR() would use "true".
+ Introduce DEFINE_PROP_CHR_NO_CONNECT() that would use "false".
and wire it with a new PropertyInfo and modified callbacks.
> }
>
> if (s) {
> @@ -218,6 +226,11 @@ bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error
> **errp)
> return true;
> }
>
> +bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp)
> +{
> + return qemu_chr_fe_init_ex(b, s, NULL, errp);
> +}
> +
> void qemu_chr_fe_deinit(CharBackend *b, bool del)
> {
> assert(b);
> diff --git a/hw/core/qdev-properties-system.c
> b/hw/core/qdev-properties-system.c
> index 1f810b7ddf..35eed17d4d 100644
> --- a/hw/core/qdev-properties-system.c
> +++ b/hw/core/qdev-properties-system.c
> @@ -297,7 +297,7 @@ static void set_chr(Object *obj, Visitor *v, const char
> *name, void *opaque,
> if (s == NULL) {
> error_setg(errp, "Property '%s.%s' can't find value '%s'",
> object_get_typename(obj), name, str);
> - } else if (!qemu_chr_fe_init(be, s, errp)) {
> + } else if (!qemu_chr_fe_init_ex(be, s, obj->class, errp)) {
> error_prepend(errp, "Property '%s.%s' can't take value '%s': ",
> object_get_typename(obj), name, str);
> }
> diff --git a/include/chardev/char-fe.h b/include/chardev/char-fe.h
> index 8ef05b3dd0..f1c05cc5ed 100644
> --- a/include/chardev/char-fe.h
> +++ b/include/chardev/char-fe.h
> @@ -34,6 +34,8 @@ struct CharBackend {
> * Returns: false on error.
> */
> bool qemu_chr_fe_init(CharBackend *b, Chardev *s, Error **errp);
> +bool qemu_chr_fe_init_ex(CharBackend *b, Chardev *s, ObjectClass *oc,
> + Error **errp);
>
> /**
> * qemu_chr_fe_deinit:
> --
> 2.48.1
>
>
--
Marc-André Lureau
