quorum: Create quorum.c, add QuorumChildRequest and QuorumAIOCB.

Quorum is a block filter mirroring writes to num_children children.
For reads quorum reads each children and does a vote.
If more than vote_threshold versions are identical the quorum is reached and
this winning version is returned to the guest. So quorum prevents bit corruption.
For high availability purpose minority errors are reported via QMP but the guest
does not see them.

This patch creates the driver C source file and introduces the structures that
will be used in asynchronous reads and writes.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/Makefile.objs

@@ -3,6 +3,7 @@ block-obj-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o qcow2-c
 block-obj-y += qed.o qed-gencb.o qed-l2-cache.o qed-table.o qed-cluster.o
 block-obj-y += qed-check.o
 block-obj-$(CONFIG_VHDX) += vhdx.o vhdx-endian.o vhdx-log.o
+block-obj-y += quorum.o
 block-obj-y += parallels.o blkdebug.o blkverify.o
 block-obj-y += snapshot.o qapi.o
 block-obj-$(CONFIG_WIN32) += raw-win32.o win32-aio.o

block/quorum.c

@@ -0,0 +1,53 @@
+/*
+ * Quorum Block filter
+ *
+ * Copyright (C) 2012-2014 Nodalink, EURL.
+ *
+ * Author:
+ *   Benoît Canet <benoit.canet@irqsave.net>
+ *
+ * Based on the design and code of blkverify.c (Copyright (C) 2010 IBM, Corp)
+ * and blkmirror.c (Copyright (C) 2011 Red Hat, Inc).
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "block/block_int.h"
+
+typedef struct QuorumAIOCB QuorumAIOCB;
+
+/* Quorum will create one instance of the following structure per operation it
+ * performs on its children.
+ * So for each read/write operation coming from the upper layer there will be
+ * $children_count QuorumChildRequest.
+ */
+typedef struct QuorumChildRequest {
+    BlockDriverAIOCB *aiocb;
+    QEMUIOVector qiov;
+    uint8_t *buf;
+    int ret;
+    QuorumAIOCB *parent;
+} QuorumChildRequest;
+
+/* Quorum will use the following structure to track progress of each read/write
+ * operation received by the upper layer.
+ * This structure hold pointers to the QuorumChildRequest structures instances
+ * used to do operations on each children and track overall progress.
+ */
+struct QuorumAIOCB {
+    BlockDriverAIOCB common;
+
+    /* Request metadata */
+    uint64_t sector_num;
+    int nb_sectors;
+
+    QEMUIOVector *qiov;         /* calling IOV */
+
+    QuorumChildRequest *qcrs;   /* individual child requests */
+    int count;                  /* number of completed AIOCB */
+    int success_count;          /* number of successfully completed AIOCB */
+
+    bool is_read;
+    int vote_ret;
+};