From 0c11190cdc268d88302086a79ec1741540fee907 Mon Sep 17 00:00:00 2001
From: David van Moolenbroek <david@minix3.org>
Date: Fri, 20 Apr 2012 17:23:09 +0200
Subject: [PATCH] MFS: reimplement block clean marking fix

MFS' get_block() must never return a newly acquired block buffer that
is marked dirty from previous use. This patch replaces git-dd59d50,
which assumed a working model where blocks for device NO_DEV would
never be dirty. For at least one scenario, that assumption does not
hold, triggering superblock overwrite warnings. In this patch, blocks
are explicitly marked as clean upon being repurposed. The working
model is now restored to be: the dirty state of a block is relevant
only when its associated device is not set to NO_DEV.
---
 servers/mfs/cache.c | 18 +++++++++---------
 servers/mfs/clean.h |  3 ---
 2 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/servers/mfs/cache.c b/servers/mfs/cache.c
index 9a99eb0c5..1259c5e8c 100644
--- a/servers/mfs/cache.c
+++ b/servers/mfs/cache.c
@@ -145,12 +145,12 @@ struct buf *get_block(
 	 */
 	yieldid = make64(bp->b_dev, bp->b_blocknr);
 	assert(bp->b_bytes == fs_block_size);
-	BP_CLEARDEV(bp);
+	bp->b_dev = NO_DEV;
   }
 
   /* Fill in block's parameters and add it to the hash chain where it goes. */
-  if(dev == NO_DEV) BP_CLEARDEV(bp);
-  else BP_SETDEV(bp, dev);
+  MARKCLEAN(bp);		/* NO_DEV blocks may be marked dirty */
+  bp->b_dev = dev;		/* fill in device number */
   bp->b_blocknr = block;	/* fill in block number */
   bp->b_count++;		/* record that block is being used */
   b = BUFHASH(bp->b_blocknr);
@@ -184,7 +184,7 @@ struct buf *get_block(
 
   if(only_search == PREFETCH) {
 	/* PREFETCH: don't do i/o. */
-	BP_CLEARDEV(bp);
+	bp->b_dev = NO_DEV;
   } else if (only_search == NORMAL) {
 	read_block(bp);
   } else if(only_search == NO_READ) {
@@ -351,7 +351,7 @@ register struct buf *bp;	/* buffer pointer */
 	}
 
 	if (op_failed) {
-		BP_CLEARDEV(bp);	/* invalidate block */
+		bp->b_dev = NO_DEV;	/* invalidate block */
 
 		/* Report read errors to interested parties. */
 		rdwt_err = r;
@@ -371,7 +371,7 @@ void invalidate(
   register struct buf *bp;
 
   for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++)
-	if (bp->b_dev == device) BP_CLEARDEV(bp);
+	if (bp->b_dev == device) bp->b_dev = NO_DEV;
 
   vm_forgetblocks();
 }
@@ -502,13 +502,13 @@ void rw_scattered(
 		if (r < (ssize_t) fs_block_size) {
 			/* Transfer failed. */
 			if (i == 0) {
-				BP_CLEARDEV(bp);	/* Invalidate block */
+				bp->b_dev = NO_DEV;	/* Invalidate block */
 				vm_forgetblocks();
 			}
 			break;
 		}
 		if (rw_flag == READING) {
-			BP_SETDEV(bp, dev);	/* validate block */
+			bp->b_dev = dev;	/* validate block */
 			put_block(bp, PARTIAL_DATA_BLOCK);
 		} else {
 			MARKCLEAN(bp);
@@ -663,7 +663,7 @@ void buf_pool(int new_nr_bufs)
 
   for (bp = &buf[0]; bp < &buf[nr_bufs]; bp++) {
         bp->b_blocknr = NO_BLOCK;
-	BP_CLEARDEV(bp);
+        bp->b_dev = NO_DEV;
         bp->b_next = bp + 1;
         bp->b_prev = bp - 1;
         bp->bp = NULL;
diff --git a/servers/mfs/clean.h b/servers/mfs/clean.h
index d6d112985..626c7acec 100644
--- a/servers/mfs/clean.h
+++ b/servers/mfs/clean.h
@@ -8,7 +8,4 @@
 #define ISDIRTY(b)	((b)->b_dirt == BP_DIRTY)
 #define ISCLEAN(b)	((b)->b_dirt == BP_CLEAN)
 
-#define BP_SETDEV(b, dev) do { assert((dev) != NO_DEV); (b)->b_dev = (dev); } while(0)
-#define BP_CLEARDEV(b) do { (b)->b_dev = NO_DEV; MARKCLEAN(b); } while(0)
-
 #endif