block: clarify error message for qmp-eject

If you use HMP's eject but the CDROM tray is locked, you may get a
confusing error message informing you that the "tray isn't open."

As this is the point of eject, we can do a little better and help
clarify that the tray was locked and that it (might) open up later,
so try again.

It's not ideal, but it makes the semantics of the (legacy) eject
command more understandable to end users when they try to use it.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -2281,16 +2281,29 @@ exit:
     block_job_txn_unref(block_job_txn);
 }
 
+static int do_open_tray(const char *device, bool force, Error **errp);
+
 void qmp_eject(const char *device, bool has_force, bool force, Error **errp)
 {
     Error *local_err = NULL;
+    int rc;
 
-    qmp_blockdev_open_tray(device, has_force, force, &local_err);
+    if (!has_force) {
+        force = false;
+    }
+
+    rc = do_open_tray(device, force, &local_err);
     if (local_err) {
         error_propagate(errp, local_err);
         return;
     }
 
+    if (rc == EINPROGRESS) {
+        error_setg(errp, "Device '%s' is locked and force was not specified, "
+                   "wait for tray to open and try again", device);
+        return;
+    }
+
     qmp_x_blockdev_remove_medium(device, errp);
 }
 
@@ -2318,35 +2331,36 @@ void qmp_block_passwd(bool has_device, const char *device,
     aio_context_release(aio_context);
 }
 
-void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
-                            Error **errp)
+/**
+ * returns -errno on fatal error, +errno for non-fatal situations.
+ * errp will always be set when the return code is negative.
+ * May return +ENOSYS if the device has no tray,
+ * or +EINPROGRESS if the tray is locked and the guest has been notified.
+ */
+static int do_open_tray(const char *device, bool force, Error **errp)
 {
     BlockBackend *blk;
     bool locked;
 
-    if (!has_force) {
-        force = false;
-    }
-
     blk = blk_by_name(device);
     if (!blk) {
         error_set(errp, ERROR_CLASS_DEVICE_NOT_FOUND,
                   "Device '%s' not found", device);
-        return;
+        return -ENODEV;
     }
 
     if (!blk_dev_has_removable_media(blk)) {
         error_setg(errp, "Device '%s' is not removable", device);
-        return;
+        return -ENOTSUP;
     }
 
     if (!blk_dev_has_tray(blk)) {
         /* Ignore this command on tray-less devices */
-        return;
+        return ENOSYS;
     }
 
     if (blk_dev_is_tray_open(blk)) {
-        return;
+        return 0;
     }
 
     locked = blk_dev_is_medium_locked(blk);
@@ -2357,6 +2371,21 @@ void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
     if (!locked || force) {
         blk_dev_change_media_cb(blk, false);
     }
+
+    if (locked && !force) {
+        return EINPROGRESS;
+    }
+
+    return 0;
+}
+
+void qmp_blockdev_open_tray(const char *device, bool has_force, bool force,
+                            Error **errp)
+{
+    if (!has_force) {
+        force = false;
+    }
+    do_open_tray(device, force, errp);
 }
 
 void qmp_blockdev_close_tray(const char *device, Error **errp)