Make pin/unpin explicit

kernel/bio.c

@@ -133,3 +133,19 @@ brelse(struct buf *b)
   
   release(&bcache.lock);
 }
+
+void
+bpin(struct buf *b) {
+  acquire(&bcache.lock);
+  b->refcnt++;
+  release(&bcache.lock);
+}
+
+void
+bunpin(struct buf *b) {
+  acquire(&bcache.lock);
+  b->refcnt--;
+  release(&bcache.lock);
+}
+
+

kernel/defs.h

@@ -14,6 +14,8 @@ void            binit(void);
 struct buf*     bread(uint, uint);
 void            brelse(struct buf*);
 void            bwrite(struct buf*);
+void            bpin(struct buf*);
+void            bunpin(struct buf*);
 
 // console.c
 void            consoleinit(void);

kernel/log.c

@@ -77,7 +77,7 @@ install_trans(void)
     struct buf *dbuf = bread(log.dev, log.lh.block[tail]); // read dst
     memmove(dbuf->data, lbuf->data, BSIZE);  // copy block to dst
     bwrite(dbuf);  // write dst to disk
-    dbuf->refcnt--;  // unpin buffer from cache
+    bunpin(dbuf);
     brelse(lbuf);
     brelse(dbuf);
   }
@@ -229,7 +229,7 @@ log_write(struct buf *b)
   }
   log.lh.block[i] = b->blockno;
   if (i == log.lh.n) {  // Add new block to log?
-    b->refcnt++;  // Pin block in cache
+    bpin(b);
     log.lh.n++;
   }
   release(&log.lock);