char: Allow devices to use a single multiplexed chardev.

This fixes regression caused by commit
2d6c1ef40f
("char: Prevent multiple devices opening same chardev"):

-nodefaults -nographic -chardev stdio,id=stdio,mux=on,signal=off \
 -mon stdio -device virtio-serial-pci \
 -device virtconsole,chardev=stdio -device isa-serial,chardev=stdio

fails with:

qemu-system-x86_64: -device isa-serial,chardev=stdio: Property 'isa-serial.chardev' can't take value 'stdio', it's in use

Signed-off-by: Kusanagi Kouichi <slash@ac.auone-net.jp>
Signed-off-by: Amit Shah <amit.shah@redhat.com>

hw/qdev-properties.c

@@ -354,10 +354,10 @@ static int parse_chr(DeviceState *dev, Property *prop, const char *str)
     if (*ptr == NULL) {
         return -ENOENT;
     }
-    if ((*ptr)->assigned) {
+    if ((*ptr)->avail_connections < 1) {
         return -EEXIST;
     }
-    (*ptr)->assigned = 1;
+    --(*ptr)->avail_connections;
     return 0;
 }
 

qemu-char.c

@@ -199,7 +199,7 @@ void qemu_chr_add_handlers(CharDriverState *s,
 {
     if (!opaque) {
         /* chr driver being released. */
-        s->assigned = 0;
+        ++s->avail_connections;
     }
     s->chr_can_read = fd_can_read;
     s->chr_read = fd_read;
@@ -2547,7 +2547,10 @@ CharDriverState *qemu_chr_open_opts(QemuOpts *opts,
         snprintf(base->label, len, "%s-base", qemu_opts_id(opts));
         chr = qemu_chr_open_mux(base);
         chr->filename = base->filename;
+        chr->avail_connections = MAX_MUX;
         QTAILQ_INSERT_TAIL(&chardevs, chr, next);
+    } else {
+        chr->avail_connections = 1;
     }
     chr->label = qemu_strdup(qemu_opts_id(opts));
     return chr;

qemu-char.h

@@ -72,7 +72,7 @@ struct CharDriverState {
     char *label;
     char *filename;
     int opened;
-    int assigned; /* chardev assigned to a device */
+    int avail_connections;
     QTAILQ_ENTRY(CharDriverState) next;
 };