libminixfs: fix buf leak

. mfs: add asserts to catch similar problems in the future

Change-Id: I939230b8d63f100ac071696425b35496b2169bc4

lib/libminixfs/cache.c

@@ -619,6 +619,23 @@ void lmfs_rw_scattered(
   static iovec_t iovec[NR_IOREQS];
   u64_t pos;
   int iov_per_block;
+  int start_in_use = bufs_in_use, start_bufqsize = bufqsize;
+
+  assert(bufqsize >= 0);
+  if(bufqsize == 0) return;
+
+  /* for READING, check all buffers on the list are obtained and held
+   * (count > 0)
+   */
+  if (rw_flag == READING) {
+	for(i = 0; i < bufqsize; i++) {
+		assert(bufq[i] != NULL);
+		assert(bufq[i]->lmfs_count > 0);
+  	}
+
+  	/* therefore they are all 'in use' and must be at least this many */
+	  assert(start_in_use >= start_bufqsize);
+  }
 
   assert(dev != NO_DEV);
   assert(!(fs_block_size % PAGE_SIZE));
@@ -700,8 +717,10 @@ void lmfs_rw_scattered(
 		}
 		r -= fs_block_size;
 	}
-	bufq += nblocks;
+
-	bufqsize -= nblocks;
+	bufq += i;
+	bufqsize -= i;
+
 	if (rw_flag == READING) {
 		/* Don't bother reading more than the device is willing to
 		 * give at this time.  Don't forget to release those extras.
@@ -720,6 +739,13 @@ void lmfs_rw_scattered(
 		break;
 	}
   }
+
+  if(rw_flag == READING) {
+  	assert(start_in_use >= start_bufqsize);
+
+	/* READING callers assume all bufs are released. */
+	assert(start_in_use - start_bufqsize == bufs_in_use);
+  }
 }
 
 /*===========================================================================*

servers/mfs/read.c

@@ -297,7 +297,7 @@ int *completed;			/* number of bytes copied */
   }
 
   /* In all cases, bp now points to a valid buffer. */
-  assert(bp);
+  assert(bp != NULL);
   
   if (rw_flag == WRITING && chunk != block_size && !block_spec &&
       (off_t) ex64lo(position) >= rip->i_size && off == 0) {
@@ -477,6 +477,7 @@ unsigned bytes_ahead;		/* bytes beyond position for immediate use */
   static unsigned int readqsize = 0;
   static struct buf **read_q;
   u64_t position_running;
+  int inuse_before = lmfs_bufs_in_use();
 
   if(readqsize != nr_bufs) {
 	if(readqsize > 0) {
@@ -512,6 +513,7 @@ unsigned bytes_ahead;		/* bytes beyond position for immediate use */
 	  bp = lmfs_get_block_ino(dev, block, PREFETCH, rip->i_num, position);
 
   assert(bp != NULL);
+  assert(bp->lmfs_count > 0);
   if (lmfs_dev(bp) != NO_DEV) return(bp);
 
   /* The best guess for the number of blocks to prefetch:  A lot.
@@ -567,6 +569,7 @@ unsigned bytes_ahead;		/* bytes beyond position for immediate use */
   /* Acquire block buffers. */
   for (;;) {
   	block_t thisblock;
+	assert(bp->lmfs_count > 0);
 	read_q[read_q_size++] = bp;
 
 	if (--blocks_ahead == 0) break;
@@ -583,6 +586,8 @@ unsigned bytes_ahead;		/* bytes beyond position for immediate use */
 	} else {
 		bp = get_block(dev, block, PREFETCH);
 	}
+	assert(bp);
+	assert(bp->lmfs_count > 0);
 	if (lmfs_dev(bp) != NO_DEV) {
 		/* Oops, block already in the cache, get out. */
 		put_block(bp, FULL_DATA_BLOCK);
@@ -591,6 +596,8 @@ unsigned bytes_ahead;		/* bytes beyond position for immediate use */
   }
   lmfs_rw_scattered(dev, read_q, read_q_size, READING);
 
+  assert(inuse_before == lmfs_bufs_in_use());
+
   if(block_spec)
 	  return get_block(dev, baseblock, NORMAL);
   return(lmfs_get_block_ino(dev, baseblock, NORMAL, rip->i_num, position));