Decrypt VFP can read multiple records per fetch chunk.

This entails having a max_chunk parameter, currently hard-wired to
match default fetch_chunksize, but will become configurable.

In a perfect world, max_chunk would be automatically set to the
current value of fetch_chunksize -- setting it larger would be
unsafe. But since we can't read cache_param without violating
the API, we can only warn users not to do that. *sigh*

src/vfp.c

@@ -40,6 +40,9 @@
 
 #define HDR_PREFIX_LEN (SALT_LEN + 4 + 1)
 #define ID_LEN 255
+/* XXX currently hard-wired, will be configurable */
+/* matches default fetch_chunksize */
+#define DEFAULT_MAX_CHUNK (16 * 1024)
 
 #define ERR_DEC(ctx, msg)			\
 	VFP_Error((ctx), "ece decrypt: " msg)
@@ -61,6 +64,7 @@ struct ece {
 	struct ece_crypto	*crypto;
 	EVP_CIPHER_CTX		*ectx;
 	uint8_t			*buf;
+	size_t			fetchsz;
 	uint64_t		seq_lo;
 	uint32_t		seq_hi;
 	uint32_t		rs;
@@ -163,6 +167,10 @@ decrypt_init(struct ece *ece, struct vfp_ctx *ctx)
 	ece->crypto->prenonce_hi = vbe32dec(prenonce);
 	ece->crypto->prenonce_lo = vbe64dec(prenonce + 4);
 
+	/* XXX make max_chunk configurable */
+	ece->fetchsz = (DEFAULT_MAX_CHUNK / ece->rs) * ece->rs;
+	if (ece->fetchsz == 0)
+		ece->fetchsz = ece->rs;
 	memcpy(ece->crypto->cek, cek, AES128_KEYLEN);
 	return (VFP_OK);
 }
@@ -312,7 +320,8 @@ vfp_decrypt_pull(struct vfp_ctx *ctx, struct vfp_entry *ent, void *ptr,
 {
 	struct ece *ece;
 	size_t len;
-	enum vfp_status vp;
+	void *p = ptr;
+	enum vfp_status vp, fetch_vp;
 
 	CHECK_OBJ_NOTNULL(ctx, VFP_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(ent, VFP_ENTRY_MAGIC);
@@ -320,19 +329,30 @@ vfp_decrypt_pull(struct vfp_ctx *ctx, struct vfp_entry *ent, void *ptr,
 	AN(ptr);
 	AN(lenp);
 
-	*lenp = 0;
 	if (ece->rs == 0)
 		if ((vp = decrypt_init(ece, ctx)) != VFP_OK)
 			return (vp);
 	AN(ece->rs);
+	AN(ece->fetchsz);
 	AN(ece->buf);
-	len = ece->rs;
-	vp = suck_bytes(ctx, ece->buf, &len);
-	assert(len <= ece->rs);
-	if (vp == VFP_ERROR)
-		return (vp);
-	vp = decrypt(ece, ctx, ptr, &len, vp);
-	*lenp = len;
+
+	len = ece->fetchsz;
+	fetch_vp = suck_bytes(ctx, ece->buf, &len);
+	if (fetch_vp == VFP_ERROR)
+		return (fetch_vp);
+
+	for (size_t in = len; vp == VFP_OK && in > 0; ece->buf += ece->rs) {
+		len = ece->rs;
+		if (in < len)
+			len = in;
+		vp = VFP_OK;
+		if (in <= ece->rs)
+			vp = fetch_vp;
+		in -= len;
+		vp = decrypt(ece, ctx, p, &len, vp);
+		p += len;
+	}
+	*lenp = p - ptr;
 	return (vp);
 }