chardev/mux: introduce `mux_chr_attach_frontend() call

Move away logic which attaches frontend device to a mux
from `char-fe.c` to actual `char-mux.c` implementation
and make it a separate function.

No logic changes are made.

Signed-off-by: Roman Penyaev <r.peniaev@gmail.com>
Cc: "Marc-André Lureau" <marcandre.lureau@redhat.com>
Cc: qemu-devel@nongnu.org
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20241014152408.427700-6-r.peniaev@gmail.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/chardev/char-mux.c b/chardev/char-mux.c
index b2d7abf2fc..9294f95546 100644
--- a/chardev/char-mux.c
+++ b/chardev/char-mux.c
@@ -301,6 +301,23 @@ static void mux_chr_update_read_handlers(Chardev *chr)
                                   chr->gcontext, true, false);
 }
 
+bool mux_chr_attach_frontend(MuxChardev *d, CharBackend *b,
+                             unsigned int *tag, Error **errp)
+{
+    if (d->mux_cnt >= MAX_MUX) {
+        error_setg(errp,
+                   "too many uses of multiplexed chardev '%s'"
+                   " (maximum is " stringify(MAX_MUX) ")",
+                   d->parent.label);
+        return false;
+    }
+
+    d->backends[d->mux_cnt] = b;
+    *tag = d->mux_cnt++;
+
+    return true;
+}
+
 void mux_set_focus(Chardev *chr, unsigned int focus)
 {
     MuxChardev *d = MUX_CHARDEV(chr);