[src/trunk]: src/sys/kern comments

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

details:   https://anonhg.NetBSD.org/src/rev/03b067f7bec2
branches:  trunk
changeset: 772661:03b067f7bec2
user:      yamt <yamt%NetBSD.org@localhost>
date:      Wed Jan 11 00:11:32 2012 +0000

description:
comments

diffstat:

 sys/kern/vfs_wapbl.c |  17 ++++++++++++++---
 1 files changed, 14 insertions(+), 3 deletions(-)

diffs (52 lines):

diff -r 9d4cb3cf999f -r 03b067f7bec2 sys/kern/vfs_wapbl.c
--- a/sys/kern/vfs_wapbl.c      Tue Jan 10 23:39:11 2012 +0000
+++ b/sys/kern/vfs_wapbl.c      Wed Jan 11 00:11:32 2012 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_wapbl.c,v 1.48 2011/12/02 12:38:59 yamt Exp $      */
+/*     $NetBSD: vfs_wapbl.c,v 1.49 2012/01/11 00:11:32 yamt Exp $      */
 
 /*-
  * Copyright (c) 2003, 2008, 2009 The NetBSD Foundation, Inc.
@@ -36,7 +36,7 @@
 #define WAPBL_INTERNAL
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_wapbl.c,v 1.48 2011/12/02 12:38:59 yamt Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_wapbl.c,v 1.49 2012/01/11 00:11:32 yamt Exp $");
 
 #include <sys/param.h>
 #include <sys/bitops.h>
@@ -1956,7 +1956,12 @@
        int error;
        daddr_t pbn;
 
-       /* XXX Calc checksum here, instead we do this for now */
+       /*
+        * flush disk cache to ensure that blocks we've written are actually
+        * written to the stable storage before the commit header.
+        *
+        * XXX Calc checksum here, instead we do this for now
+        */
        wapbl_cache_sync(wl, "1");
 
        wc->wc_head = head;
@@ -1972,6 +1977,8 @@
            (intmax_t)head, (intmax_t)tail));
 
        /*
+        * write the commit header.
+        *
         * XXX if generation will rollover, then first zero
         * over second commit header before trying to write both headers.
         */
@@ -1984,6 +1991,10 @@
        if (error)
                return error;
 
+       /*
+        * flush disk cache to ensure that the commit header is actually
+        * written before meta data blocks.
+        */
        wapbl_cache_sync(wl, "2");
 
        /*