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 71e8e034974ce154b9d1e54021be8955ec404c91..b4b5e180c9109963c42685e0625b6abd6f039097 100644 (file)
--- 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);