atapi: Explain why we need a 'media not present' state

After the re-org of the atapi code, it might not be intuitive for a
reader of the code to understand why we're inserting a 'media not
present' state between cd changes.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

diff --git a/hw/ide/atapi.c b/hw/ide/atapi.c
index 86b18d8..58febc0 100644 (file)
--- a/hw/ide/atapi.c
+++ b/hw/ide/atapi.c
@@ -1106,7 +1106,13 @@ void ide_atapi_cmd(IDEState *s)
         ide_atapi_cmd_check_status(s);
         return;
     }
-
+    /*
+     * When a CD gets changed, we have to report an ejected state and
+     * then a loaded state to guests so that they detect tray
+     * open/close and media change events.  Guests that do not use
+     * GET_EVENT_STATUS_NOTIFICATION to detect such tray open/close
+     * states rely on this behavior.
+     */
     if (bdrv_is_inserted(s->bs) && s->cdrom_changed) {
         ide_atapi_cmd_error(s, SENSE_NOT_READY, ASC_MEDIUM_NOT_PRESENT);