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.

diff --git a/servers/mfs/cache.c b/servers/mfs/cache.c
index 9a99eb0c51d067d81fb2b39d04e316dd80cdb6a2..1259c5e8c59c628383cc9710c7adff4ccbe67a6a 100644 (file)
--- 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 d6d112985b0aa4d900c85d4cbcbd68aebde1dc6f..626c7aceca61dba8ce8083c3931eb4fb3abc0653 100644 (file)
--- 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