[RFC] gdbstub: propagate Error to gdbserver_start (and other device setups)

diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index d73f424f56..0675b0b646 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -49,12 +49,18 @@  void gdb_unregister_coprocessor_all(CPUState *cpu);
 /**
  * gdbserver_start: start the gdb server
  * @port_or_device: connection spec for gdb
+ * @errp: error handle
  *
  * For CONFIG_USER this is either a tcp port or a path to a fifo. For
  * system emulation you can use a full chardev spec for your gdbserver
  * port.
+ *
+ * The error handle should be either &error_fatal (for start-up) or
+ * &error_warn (for QMP/HMP initiated sessions).
+ *
+ * Returns true when server successfully started.
  */
-int gdbserver_start(const char *port_or_device);
+bool gdbserver_start(const char *port_or_device, Error **errp);
 
 /**
  * gdb_feature_builder_init() - Initialize GDBFeatureBuilder.
diff --git a/gdbstub/system.c b/gdbstub/system.c
index 2d9fdff2fe..8ce79fa88c 100644
--- a/gdbstub/system.c
+++ b/gdbstub/system.c
@@ -330,26 +330,27 @@  static void create_processes(GDBState *s)
     gdb_create_default_process(s);
 }
 
-int gdbserver_start(const char *device)
+bool gdbserver_start(const char *device, Error **errp)
 {
     Chardev *chr = NULL;
     Chardev *mon_chr;
     g_autoptr(GString) cs = g_string_new(device);
 
     if (!first_cpu) {
-        error_report("gdbstub: meaningless to attach gdb to a "
-                     "machine without any CPU.");
-        return -1;
+        error_setg(errp, "gdbstub: meaningless to attach gdb to a "
+                   "machine without any CPU.");
+        return false;
     }
 
     if (!gdb_supports_guest_debug()) {
-        error_report("gdbstub: current accelerator doesn't "
-                     "support guest debugging");
-        return -1;
+        error_setg(errp, "gdbstub: current accelerator doesn't "
+                   "support guest debugging");
+        return false;
     }
 
     if (cs->len == 0) {
-        return -1;
+        error_setg(errp, "gdbstub: missing connection string");
+        return false;
     }
 
     trace_gdbstub_op_start(cs->str);
@@ -374,7 +375,8 @@  int gdbserver_start(const char *device)
          */
         chr = qemu_chr_new_noreplay("gdb", cs->str, true, NULL);
         if (!chr) {
-            return -1;
+            error_setg(errp, "gdbstub: couldn't create chardev");
+            return false;
         }
     }
 
@@ -406,7 +408,7 @@  int gdbserver_start(const char *device)
     gdbserver_system_state.mon_chr = mon_chr;
     gdb_syscall_reset();
 
-    return 0;
+    return true;
 }
 
 static void register_types(void)
diff --git a/gdbstub/user.c b/gdbstub/user.c
index 0b4bfa9c48..fb8f6867ea 100644
--- a/gdbstub/user.c
+++ b/gdbstub/user.c
@@ -13,6 +13,7 @@ 
 #include "qemu/bitops.h"
 #include "qemu/cutils.h"
 #include "qemu/sockets.h"
+#include "qapi/error.h"
 #include "exec/hwaddr.h"
 #include "exec/tb-flush.h"
 #include "exec/gdbstub.h"
@@ -372,15 +373,15 @@  static bool gdb_accept_tcp(int gdb_fd)
     return true;
 }
 
-static int gdbserver_open_port(int port)
+static int gdbserver_open_port(int port, Error **errp)
 {
     struct sockaddr_in sockaddr;
     int fd, ret;
 
     fd = socket(PF_INET, SOCK_STREAM, 0);
     if (fd < 0) {
-        perror("socket");
-        return -1;
+        error_setg(errp, "Failed to bind socket: %s", strerror(errno));
+        return false;
     }
     qemu_set_cloexec(fd);
 
@@ -405,31 +406,32 @@  static int gdbserver_open_port(int port)
     return fd;
 }
 
-int gdbserver_start(const char *port_or_path)
+bool gdbserver_start(const char *port_or_path, Error **errp)
 {
     int port = g_ascii_strtoull(port_or_path, NULL, 10);
     int gdb_fd;
 
     if (port > 0) {
-        gdb_fd = gdbserver_open_port(port);
+        gdb_fd = gdbserver_open_port(port, errp);
     } else {
         gdb_fd = gdbserver_open_socket(port_or_path);
     }
 
     if (gdb_fd < 0) {
-        return -1;
+        return false;
     }
 
     if (port > 0 && gdb_accept_tcp(gdb_fd)) {
-        return 0;
+        return true;
     } else if (gdb_accept_socket(gdb_fd)) {
         gdbserver_user_state.socket_path = g_strdup(port_or_path);
-        return 0;
+        return true;
     }
 
     /* gone wrong */
     close(gdb_fd);
-    return -1;
+    error_setg(errp, "gdbstub: failed to accept connection");
+    return false;
 }
 
 void gdbserver_fork_start(void)
diff --git a/linux-user/main.c b/linux-user/main.c
index b97634a32d..7198fa0986 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -1023,11 +1023,7 @@  int main(int argc, char **argv, char **envp)
     target_cpu_copy_regs(env, regs);
 
     if (gdbstub) {
-        if (gdbserver_start(gdbstub) < 0) {
-            fprintf(stderr, "qemu: could not open gdbserver on %s\n",
-                    gdbstub);
-            exit(EXIT_FAILURE);
-        }
+        gdbserver_start(gdbstub, &error_fatal);
         gdb_handlesig(cpu, 0, NULL, NULL, 0);
     }
 
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index 80b2e5ff9f..0aa22e1ae2 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -285,7 +285,7 @@  void hmp_gdbserver(Monitor *mon, const QDict *qdict)
         device = "tcp::" DEFAULT_GDBSTUB_PORT;
     }
 
-    if (gdbserver_start(device) < 0) {
+    if (!gdbserver_start(device, &error_warn)) {
         monitor_printf(mon, "Could not open gdbserver on device '%s'\n",
                        device);
     } else if (strcmp(device, "none") == 0) {
diff --git a/system/vl.c b/system/vl.c
index 0843b7ab49..1d2ca77b7f 100644
--- a/system/vl.c
+++ b/system/vl.c
@@ -811,29 +811,13 @@  static void configure_msg(QemuOpts *opts)
 /***********************************************************/
 /* USB devices */
 
-static int usb_device_add(const char *devname)
+static bool usb_parse(const char *devname, Error **errp)
 {
-    USBDevice *dev = NULL;
-
-    if (!machine_usb(current_machine)) {
-        return -1;
-    }
-
-    dev = usbdevice_create(devname);
-    if (!dev)
-        return -1;
-
-    return 0;
-}
-
-static int usb_parse(const char *cmdline)
-{
-    int r;
-    r = usb_device_add(cmdline);
-    if (r < 0) {
-        error_report("could not add USB device '%s'", cmdline);
+    if (!usbdevice_create(devname)) {
+        error_setg(errp, "could not add USB device '%s'", devname);
+        return false;
     }
-    return r;
+    return true;
 }
 
 /***********************************************************/
@@ -1307,22 +1291,20 @@  static void add_device_config(int type, const char *cmdline)
     QTAILQ_INSERT_TAIL(&device_configs, conf, next);
 }
 
-static int foreach_device_config(int type, int (*func)(const char *cmdline))
+/*
+ * Run through the special device configs, any error will exit via error_fatal.
+ */
+static void foreach_device_config(int type, bool (*func)(const char *cmdline, Error **errp))
 {
     struct device_config *conf;
-    int rc;
 
     QTAILQ_FOREACH(conf, &device_configs, next) {
         if (conf->type != type)
             continue;
         loc_push_restore(&conf->loc);
-        rc = func(conf->cmdline);
+        func(conf->cmdline, &error_fatal);
         loc_pop(&conf->loc);
-        if (rc) {
-            return rc;
-        }
     }
-    return 0;
 }
 
 static void qemu_disable_default_devices(void)
@@ -1452,7 +1434,7 @@  static void qemu_create_default_devices(void)
     }
 }
 
-static int serial_parse(const char *devname)
+static bool serial_parse(const char *devname, Error **errp)
 {
     int index = num_serial_hds;
 
@@ -1467,13 +1449,13 @@  static int serial_parse(const char *devname)
 
         serial_hds[index] = qemu_chr_new_mux_mon(label, devname, NULL);
         if (!serial_hds[index]) {
-            error_report("could not connect serial device"
-                         " to character backend '%s'", devname);
-            return -1;
+            error_setg(errp, "could not connect serial device"
+                       " to character backend '%s'", devname);
+            return false;
         }
     }
     num_serial_hds++;
-    return 0;
+    return true;
 }
 
 Chardev *serial_hd(int i)
@@ -1485,44 +1467,44 @@  Chardev *serial_hd(int i)
     return NULL;
 }
 
-static int parallel_parse(const char *devname)
+static bool parallel_parse(const char *devname, Error **errp)
 {
     static int index = 0;
     char label[32];
 
     if (strcmp(devname, "none") == 0)
-        return 0;
+        return true;
     if (index == MAX_PARALLEL_PORTS) {
-        error_report("too many parallel ports");
-        exit(1);
+        error_setg(errp, "too many parallel ports");
+        return false;
     }
     snprintf(label, sizeof(label), "parallel%d", index);
     parallel_hds[index] = qemu_chr_new_mux_mon(label, devname, NULL);
     if (!parallel_hds[index]) {
-        error_report("could not connect parallel device"
-                     " to character backend '%s'", devname);
-        return -1;
+        error_setg(errp, "could not connect parallel device"
+                   " to character backend '%s'", devname);
+        return false;
     }
     index++;
-    return 0;
+    return true;
 }
 
-static int debugcon_parse(const char *devname)
+static bool debugcon_parse(const char *devname, Error **errp)
 {
     QemuOpts *opts;
 
     if (!qemu_chr_new_mux_mon("debugcon", devname, NULL)) {
-        error_report("invalid character backend '%s'", devname);
-        exit(1);
+        error_setg(errp, "invalid character backend '%s'", devname);
+        return false;
     }
     opts = qemu_opts_create(qemu_find_opts("device"), "debugcon", 1, NULL);
     if (!opts) {
-        error_report("already have a debugcon device");
-        exit(1);
+        error_setg(errp, "already have a debugcon device");
+        return false;
     }
     qemu_opt_set(opts, "driver", "isa-debugcon", &error_abort);
     qemu_opt_set(opts, "chardev", "debugcon", &error_abort);
-    return 0;
+    return true;
 }
 
 static gint machine_class_cmp(gconstpointer a, gconstpointer b)
@@ -2044,12 +2026,10 @@  static void qemu_create_late_backends(void)
     qemu_opts_foreach(qemu_find_opts("mon"),
                       mon_init_func, NULL, &error_fatal);
 
-    if (foreach_device_config(DEV_SERIAL, serial_parse) < 0)
-        exit(1);
-    if (foreach_device_config(DEV_PARALLEL, parallel_parse) < 0)
-        exit(1);
-    if (foreach_device_config(DEV_DEBUGCON, debugcon_parse) < 0)
-        exit(1);
+    /* failures here will exit via error_fatal */
+    foreach_device_config(DEV_SERIAL, serial_parse);
+    foreach_device_config(DEV_PARALLEL, parallel_parse);
+    foreach_device_config(DEV_DEBUGCON, debugcon_parse);
 
     /* now chardevs have been created we may have semihosting to connect */
     qemu_semihosting_chardev_init();
@@ -2668,10 +2648,9 @@  static void qemu_create_cli_devices(void)
     qemu_opts_foreach(qemu_find_opts("fw_cfg"),
                       parse_fw_cfg, fw_cfg_find(), &error_fatal);
 
-    /* init USB devices */
+    /* init USB devices, failure will exit */
     if (machine_usb(current_machine)) {
-        if (foreach_device_config(DEV_USB, usb_parse) < 0)
-            exit(1);
+        foreach_device_config(DEV_USB, usb_parse);
     }
 
     /* init generic devices */
@@ -2718,10 +2697,9 @@  static bool qemu_machine_creation_done(Error **errp)
         exit(1);
     }
 
-    if (foreach_device_config(DEV_GDB, gdbserver_start) < 0) {
-        error_setg(errp, "could not start gdbserver");
-        return false;
-    }
+    /* failure will exit via error_fatal */
+    foreach_device_config(DEV_GDB, gdbserver_start);
+
     if (!vga_interface_created && !default_vga &&
         vga_interface_type != VGA_NONE) {
         warn_report("A -vga option was passed but this machine "