From: David van Moolenbroek <david@minix3.org>
Date: Sun, 29 Mar 2015 12:30:45 +0000 (+0000)
Subject: libminixfs: do not flush blocks that are in use
X-Git-Url: http://zhaoyanbai.com/repos/%22http:/www.isc.org/icons/zpipe.c?a=commitdiff_plain;h=b8f6d4a649d44c98668d0080b8824a48816ae4b0;p=minix.git

libminixfs: do not flush blocks that are in use

This removes an implicit requirement for the way the libminixfs API is
to be used, namely that a block is to be marked as dirty only once its
contents have been fully updated, within a single get_block/put_block
window.  The requirement may not be appropriate for all file systems.

Change-Id: I6a129d51b1a5e9aec1572039dc7c1c82dd795db5
---

diff --git a/minix/lib/libminixfs/cache.c b/minix/lib/libminixfs/cache.c
index 71e8e0349..b4b5e180c 100644
--- a/minix/lib/libminixfs/cache.c
+++ b/minix/lib/libminixfs/cache.c
@@ -732,7 +732,7 @@ void lmfs_flushdev(dev_t dev)
 /* Flush all dirty blocks for one device. */
 
   register struct buf *bp;
-  static struct buf **dirty;	/* static so it isn't on stack */
+  static struct buf **dirty;
   static unsigned int dirtylistsize = 0;
   int ndirty;
 
@@ -747,9 +747,13 @@ void lmfs_flushdev(dev_t dev)
   }
 
   for (bp = &buf[0], ndirty = 0; bp < &buf[nr_bufs]; bp++) {
-       if (!lmfs_isclean(bp) && bp->lmfs_dev == dev) {
-               dirty[ndirty++] = bp;
-       }
+	/* Do not flush dirty blocks that are in use (lmfs_count>0): the file
+	 * system may mark the block as dirty before changing its contents, in
+	 * which case the new contents could end up being lost.
+	 */
+	if (!lmfs_isclean(bp) && bp->lmfs_dev == dev && bp->lmfs_count == 0) {
+		dirty[ndirty++] = bp;
+	}
   }
 
   lmfs_rw_scattered(dev, dirty, ndirty, WRITING);