qemu-char: ask and print error information from qemu-sockets

Before:

    $ qemu-system-x86_64 -monitor tcp:localhost:6000
    (starts despite error)

    $ qemu-system-x86_64 -monitor tcp:foo.bar:12345
    getaddrinfo(foo.bar,12345): Name or service not known
    chardev: opening backend "socket" failed

    $ qemu-system-x86_64 -monitor tcp:localhost:443,server=on
    inet_listen_opts: bind(ipv4,127.0.0.1,443): Permission denied
    inet_listen_opts: FAILED
    chardev: opening backend "socket" failed

After:

    $ x86_64-softmmu/qemu-system-x86_64 -monitor tcp:localhost:6000
    x86_64-softmmu/qemu-system-x86_64: -monitor tcp:localhost:6000: Failed to connect to socket: Connection refused
    chardev: opening backend "socket" failed

    $ x86_64-softmmu/qemu-system-x86_64 -monitor tcp:foo.bar:12345
    qemu-system-x86_64: -monitor tcp:foo.bar:12345: address resolution failed for foo.bar:12345: Name or service not known
    chardev: opening backend "socket" failed

    $ x86_64-softmmu/qemu-system-x86_64 -monitor tcp:localhost:443,server=on
    qemu-system-x86_64: -monitor tcp:localhost:443,server=on: Failed to bind socket: Permission denied
    chardev: opening backend "socket" failed
Reviewed-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

qemu-char.c

@@ -2097,12 +2097,13 @@ static CharDriverState *qemu_chr_open_udp(QemuOpts *opts)
 {
     CharDriverState *chr = NULL;
     NetCharDriver *s = NULL;
+    Error *local_err = NULL;
     int fd = -1;
 
     chr = g_malloc0(sizeof(CharDriverState));
     s = g_malloc0(sizeof(NetCharDriver));
 
-    fd = inet_dgram_opts(opts, NULL);
+    fd = inet_dgram_opts(opts, &local_err);
     if (fd < 0) {
         fprintf(stderr, "inet_dgram_opts failed\n");
         goto return_err;
@@ -2118,6 +2119,10 @@ static CharDriverState *qemu_chr_open_udp(QemuOpts *opts)
     return chr;
 
 return_err:
+    if (local_err) {
+        qerror_report_err(local_err);
+        error_free(local_err);
+    }
     g_free(chr);
     g_free(s);
     if (fd >= 0) {
@@ -2428,6 +2433,7 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
 {
     CharDriverState *chr = NULL;
     TCPCharDriver *s = NULL;
+    Error *local_err = NULL;
     int fd = -1;
     int is_listen;
     int is_waitconnect;
@@ -2448,15 +2454,15 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
 
     if (is_unix) {
         if (is_listen) {
-            fd = unix_listen_opts(opts, NULL);
+            fd = unix_listen_opts(opts, &local_err);
         } else {
-            fd = unix_connect_opts(opts, NULL, NULL, NULL);
+            fd = unix_connect_opts(opts, &local_err, NULL, NULL);
         }
     } else {
         if (is_listen) {
-            fd = inet_listen_opts(opts, 0, NULL);
+            fd = inet_listen_opts(opts, 0, &local_err);
         } else {
-            fd = inet_connect_opts(opts, NULL, NULL, NULL);
+            fd = inet_connect_opts(opts, &local_err, NULL, NULL);
         }
     }
     if (fd < 0) {
@@ -2517,8 +2523,13 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
     return chr;
 
  fail:
-    if (fd >= 0)
+    if (local_err) {
+        qerror_report_err(local_err);
+        error_free(local_err);
+    }
+    if (fd >= 0) {
         closesocket(fd);
+    }
     g_free(s);
     g_free(chr);
     return NULL;