[src/trunk]: src/sys/arch/xen/xen Add a comment explaing why a flush workqueu...

[bouyer <bouyer%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/04f18f7f8486
branches:  trunk
changeset: 768077:04f18f7f8486
user:      bouyer <bouyer%NetBSD.org@localhost>
date:      Sun Aug 07 17:15:40 2011 +0000

description:
Add a comment explaing why a flush workqueue is handled differently from
read/write workqueue requests.

diffstat:

 sys/arch/xen/xen/xbdback_xenbus.c |  11 ++++++++---
 1 files changed, 8 insertions(+), 3 deletions(-)

diffs (32 lines):

diff -r cad789479c2e -r 04f18f7f8486 sys/arch/xen/xen/xbdback_xenbus.c
--- a/sys/arch/xen/xen/xbdback_xenbus.c Sun Aug 07 17:10:35 2011 +0000
+++ b/sys/arch/xen/xen/xbdback_xenbus.c Sun Aug 07 17:15:40 2011 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: xbdback_xenbus.c,v 1.43 2011/08/07 17:10:35 bouyer Exp $      */
+/*      $NetBSD: xbdback_xenbus.c,v 1.44 2011/08/07 17:15:40 bouyer Exp $      */
 
 /*
  * Copyright (c) 2006 Manuel Bouyer.
@@ -26,7 +26,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: xbdback_xenbus.c,v 1.43 2011/08/07 17:10:35 bouyer Exp $");
+__KERNEL_RCSID(0, "$NetBSD: xbdback_xenbus.c,v 1.44 2011/08/07 17:15:40 bouyer Exp $");
 
 #include <sys/types.h>
 #include <sys/param.h>
@@ -1047,7 +1047,12 @@
        xbd_io->xio_operation = xbdi->xbdi_xen_req.operation;
        xbd_io->xio_flush_id = xbdi->xbdi_xen_req.id;
        workqueue_enqueue(xbdback_workqueue, &xbdi->xbdi_io->xio_work, NULL);
-       /* xbdback_do_io() will advance req pointer and restart processing */
+       /*
+        * xbdback_do_io() will advance req pointer and restart processing.
+        * Note that we could probably set xbdi->xbdi_io to NULL and
+        * let the processing continue, but we really want to wait
+        * for the flush to complete before doing any more work.
+        */
        xbdi->xbdi_cont = xbdback_co_cache_doflush_wait;
        return NULL;
 }