bcache-utils: rewrite

They take care to avoid redundant reads now.

lib/device/bcache-utils.c

@@ -29,6 +29,16 @@ static void byte_range_to_block_range(struct bcache *cache, uint64_t start, size
 	*be = (start + len + block_size - 1) / block_size;
 }
 
+static uint64_t _min(uint64_t lhs, uint64_t rhs)
+{
+	if (rhs < lhs)
+		return rhs;
+
+	return lhs;
+}
+
+//----------------------------------------------------------------
+
 void bcache_prefetch_bytes(struct bcache *cache, int fd, uint64_t start, size_t len)
 {
 	block_address bb, be;
@@ -40,119 +50,55 @@ void bcache_prefetch_bytes(struct bcache *cache, int fd, uint64_t start, size_t
 	}
 }
 
-static uint64_t _min(uint64_t lhs, uint64_t rhs)
+//----------------------------------------------------------------
-{
-	if (rhs < lhs)
-		return rhs;
 
-	return lhs;
-}
-
-// FIXME: there's common code that can be factored out of these 3
 bool bcache_read_bytes(struct bcache *cache, int fd, uint64_t start, size_t len, void *data)
 {
 	struct block *b;
-	block_address bb, be, i;
+	block_address bb, be;
-	unsigned char *udata = data;
 	uint64_t block_size = bcache_block_sectors(cache) << SECTOR_SHIFT;
-	int errors = 0;
+	uint64_t block_offset = start % block_size;
+
+	bcache_prefetch_bytes(cache, fd, start, len);
 
 	byte_range_to_block_range(cache, start, len, &bb, &be);
-	for (i = bb; i < be; i++)
-		bcache_prefetch(cache, fd, i);
 
-	for (i = bb; i < be; i++) {
+	for (; bb != be; bb++) {
-		if (!bcache_get(cache, fd, i, 0, &b, NULL)) {
+        	if (!bcache_get(cache, fd, bb, 0, &b, NULL))
-			errors++;
+			return false;
-			continue;
-		}
-
-		if (i == bb) {
-			uint64_t block_offset = start % block_size;
-			size_t blen = _min(block_size - block_offset, len);
-			memcpy(udata, ((unsigned char *) b->data) + block_offset, blen);
-			len -= blen;
-			udata += blen;
-		} else {
-			size_t blen = _min(block_size, len);
-			memcpy(udata, b->data, blen);
-			len -= blen;
-			udata += blen;
-		}
 
+		size_t blen = _min(block_size - block_offset, len);
+		memcpy(data, ((unsigned char *) b->data) + block_offset, blen);
 		bcache_put(b);
+
+		block_offset = 0;
+		len -= blen;
+		data = ((unsigned char *) data) + blen;
 	}
 
-	return errors ? false : true;
+	return true;
-}
-
-bool bcache_write_bytes(struct bcache *cache, int fd, uint64_t start, size_t len, void *data)
-{
-	struct block *b;
-	block_address bb, be, i;
-	unsigned char *udata = data;
-	uint64_t block_size = bcache_block_sectors(cache) << SECTOR_SHIFT;
-	int errors = 0;
-
-	byte_range_to_block_range(cache, start, len, &bb, &be);
-	for (i = bb; i < be; i++)
-		bcache_prefetch(cache, fd, i);
-
-	for (i = bb; i < be; i++) {
-		if (!bcache_get(cache, fd, i, GF_DIRTY, &b, NULL)) {
-			errors++;
-			continue;
-		}
-
-		if (i == bb) {
-			uint64_t block_offset = start % block_size;
-			size_t blen = _min(block_size - block_offset, len);
-			memcpy(((unsigned char *) b->data) + block_offset, udata, blen);
-			len -= blen;
-			udata += blen;
-		} else {
-			size_t blen = _min(block_size, len);
-			memcpy(b->data, udata, blen);
-			len -= blen;
-			udata += blen;
-		}
-
-		bcache_put(b);
-	}
-
-	return errors ? false : true;
 }
 
 //----------------------------------------------------------------
 
-static bool _zero_whole_blocks(struct bcache *cache, int fd, block_address bb, block_address be)
+// Writing bytes and zeroing bytes are very similar, so we factor out
-{
+// this common code.
-	struct block *b;
+ 
-
+struct updater;
-	for (; bb != be; bb++) {
+
-		if (!bcache_get(cache, fd, bb, GF_ZERO, &b, NULL))
+typedef bool (*partial_update_fn)(struct updater *u, int fd, block_address bb, uint64_t offset, size_t len);
-        		return false;
+typedef bool (*whole_update_fn)(struct updater *u, int fd, block_address bb, block_address be);
-        	bcache_put(b);
+
-	}
+struct updater {
-
+	struct bcache *cache;
-	return true;
+	partial_update_fn partial_fn;
-}
+	whole_update_fn whole_fn;
-
+	void *data;
-static bool _zero_partial(struct bcache *cache, int fd, block_address bb, uint64_t offset, size_t len)
+};
-{
+
-	struct block *b;
+static bool _update_bytes(struct updater *u, int fd, uint64_t start, size_t len)
-
-	if (!bcache_get(cache, fd, bb, GF_DIRTY, &b, NULL))
-		return false;
-
-	memset(((unsigned char *) b->data) + offset, 0, len);
-	bcache_put(b);
-
-	return true;
-}
-
-bool bcache_zero_bytes(struct bcache *cache, int fd, uint64_t start, size_t len)
 {
+        struct bcache *cache = u->cache;
 	block_address bb, be;
 	uint64_t block_size = bcache_block_sectors(cache) << SECTOR_SHIFT;
 	uint64_t block_offset = start % block_size;
@@ -160,10 +106,15 @@ bool bcache_zero_bytes(struct bcache *cache, int fd, uint64_t start, size_t len)
 
 	byte_range_to_block_range(cache, start, len, &bb, &be);
 
+	// If the last block is partial, we will require a read, so let's 
+	// prefetch it.
+	if ((start + len) % block_size)
+        	bcache_prefetch(cache, fd, (start + len) / block_size);
+
 	// First block may be partial
 	if (block_offset) {
         	size_t blen = _min(block_size - block_offset, len);
-		if (!_zero_partial(cache, fd, bb, block_offset, blen))
+		if (!u->partial_fn(u, fd, bb, block_offset, blen))
         		return false;
 
 		len -= blen;
@@ -175,8 +126,9 @@ bool bcache_zero_bytes(struct bcache *cache, int fd, uint64_t start, size_t len)
 
         // Now we write out a set of whole blocks
         nr_whole = len / block_size;
-        if (!_zero_whole_blocks(cache, fd, bb, bb + nr_whole))
+        if (!u->whole_fn(u, fd, bb, bb + nr_whole))
                 return false;
+
 	bb += nr_whole;
 	len -= nr_whole * block_size;
 
@@ -184,7 +136,94 @@ bool bcache_zero_bytes(struct bcache *cache, int fd, uint64_t start, size_t len)
         	return true;
 
         // Finally we write a partial end block
-        return _zero_partial(cache, fd, bb, 0, len);
+        return u->partial_fn(u, fd, bb, 0, len);
+}
+
+//----------------------------------------------------------------
+
+static bool _write_partial(struct updater *u, int fd, block_address bb,
+                           uint64_t offset, size_t len)
+{
+	struct block *b;
+
+	if (!bcache_get(u->cache, fd, bb, GF_DIRTY, &b, NULL))
+		return false;
+
+	memcpy(((unsigned char *) b->data) + offset, u->data, len);
+	u->data = ((unsigned char *) u->data) + len;
+
+	bcache_put(b);
+	return true;
+}
+
+static bool _write_whole(struct updater *u, int fd, block_address bb, block_address be)
+{
+	struct block *b;
+	uint64_t block_size = bcache_block_sectors(u->cache) << SECTOR_SHIFT;
+
+	for (; bb != be; bb++) {
+        	// We don't need to read the block since we are overwriting
+        	// it completely.
+		if (!bcache_get(u->cache, fd, bb, GF_ZERO, &b, NULL))
+        		return false;
+		memcpy(b->data, u->data, block_size);
+		u->data = ((unsigned char *) u->data) + block_size;
+        	bcache_put(b);
+	}
+
+	return true;
+}
+
+bool bcache_write_bytes(struct bcache *cache, int fd, uint64_t start, size_t len, void *data)
+{
+        struct updater u;
+
+        u.cache = cache;
+        u.partial_fn = _write_partial;
+        u.whole_fn = _write_whole;
+        u.data = data;
+
+	return _update_bytes(&u, fd, start, len);
+}
+
+//----------------------------------------------------------------
+
+static bool _zero_partial(struct updater *u, int fd, block_address bb, uint64_t offset, size_t len)
+{
+	struct block *b;
+
+	if (!bcache_get(u->cache, fd, bb, GF_DIRTY, &b, NULL))
+		return false;
+
+	memset(((unsigned char *) b->data) + offset, 0, len);
+	bcache_put(b);
+
+	return true;
+}
+
+static bool _zero_whole(struct updater *u, int fd, block_address bb, block_address be)
+{
+	struct block *b;
+
+	for (; bb != be; bb++) {
+		if (!bcache_get(u->cache, fd, bb, GF_ZERO, &b, NULL))
+        		return false;
+        	bcache_put(b);
+	}
+
+	return true;
+}
+
+bool bcache_zero_bytes(struct bcache *cache, int fd, uint64_t start, size_t len)
+{
+        struct updater u;
+
+        u.cache = cache;
+        u.partial_fn = _zero_partial;
+        u.whole_fn = _zero_whole;
+        u.data = NULL;
+
+	return _update_bytes(&u, fd, start, len);
 }
 
 //----------------------------------------------------------------