[src/trunk]: src/sys/kern Clarify comment about early exit from wapbl_flush.

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

details:   https://anonhg.NetBSD.org/src/rev/c8dfb93b8728
branches:  trunk
changeset: 815251:c8dfb93b8728
user:      riastradh <riastradh%NetBSD.org@localhost>
date:      Sat May 07 21:11:51 2016 +0000

description:
Clarify comment about early exit from wapbl_flush.

Note possible bug.  Requires further analysis.

diffstat:

 sys/kern/vfs_wapbl.c |  15 +++++++++++----
 1 files changed, 11 insertions(+), 4 deletions(-)

diffs (36 lines):

diff -r e8e1ea999f3e -r c8dfb93b8728 sys/kern/vfs_wapbl.c
--- a/sys/kern/vfs_wapbl.c      Sat May 07 20:59:46 2016 +0000
+++ b/sys/kern/vfs_wapbl.c      Sat May 07 21:11:51 2016 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_wapbl.c,v 1.74 2016/05/07 20:59:46 riastradh Exp $ */
+/*     $NetBSD: vfs_wapbl.c,v 1.75 2016/05/07 21:11:51 riastradh 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 1.74 2016/05/07 20:59:46 riastradh Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_wapbl.c,v 1.75 2016/05/07 21:11:51 riastradh Exp $");
 
 #include <sys/param.h>
 #include <sys/bitops.h>
@@ -1580,8 +1580,15 @@
            wl->wl_dealloccnt);
 
        /*
-        * Now that we are fully locked and flushed,
-        * do another check for nothing to do.
+        * Now that we are exclusively locked and the file system has
+        * issued any deferred block writes for this transaction, check
+        * whether there are any blocks to write to the log.  If not,
+        * skip waiting for space or writing any log entries.
+        *
+        * XXX Shouldn't this also check wl_dealloccnt and
+        * wl_inohashcnt?  Perhaps wl_dealloccnt doesn't matter if the
+        * file system didn't produce any blocks as a consequence of
+        * it, but the same does not seem to be so of wl_inohashcnt.
         */
        if (wl->wl_bufcount == 0) {
                goto wait_out;