hmp: Fail gracefully if chardev is already in use

Trying to attach a HMP monitor to a chardev that is already in use
results in a crash because monitor_init_hmp() passes &error_abort to
qemu_chr_fe_init():

$ ./x86_64-softmmu/qemu-system-x86_64 --chardev stdio,id=foo --mon foo --mon foo
QEMU 4.2.50 monitor - type 'help' for more information
(qemu) Unexpected error in qemu_chr_fe_init() at chardev/char-fe.c:220:
qemu-system-x86_64: --mon foo: Device 'foo' is in use
Abgebrochen (Speicherabzug geschrieben)

Fix this by allowing monitor_init_hmp() to return an error and passing
any error in qemu_chr_fe_init() to its caller instead of aborting.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20200224143008.13362-19-kwolf@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/gdbstub.c b/gdbstub.c
index ce304ff482..22a2d630cd 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -3367,7 +3367,7 @@ int gdbserver_start(const char *device)
         /* Initialize a monitor terminal for gdb */
         mon_chr = qemu_chardev_new(NULL, TYPE_CHARDEV_GDB,
                                    NULL, NULL, &error_abort);
-        monitor_init_hmp(mon_chr, false);
+        monitor_init_hmp(mon_chr, false, &error_abort);
     } else {
         qemu_chr_fe_deinit(&s->chr, true);
         mon_chr = s->mon_chr;