[PATCH 9/9] kvm tools, qcow: Flush only dirty L2 tables

[Pekka Enberg <penberg@kernel.org>]

This patch improves qcow_l2_cache_write() to only flush dirty L2 tables.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
 tools/kvm/disk/qcow.c        |   11 ++++++++++-
 tools/kvm/include/kvm/qcow.h |    1 +
 2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/tools/kvm/disk/qcow.c b/tools/kvm/disk/qcow.c
index b71762f..13c8bea 100644
--- a/tools/kvm/disk/qcow.c
+++ b/tools/kvm/disk/qcow.c
@@ -93,9 +93,17 @@ static int qcow_l2_cache_write(struct qcow *q, struct qcow_l2_table *c)
 	struct qcow_header *header = q->header;
 	u64 size;
 
+	if (!c->dirty)
+		return 0;
+
 	size = 1 << header->l2_bits;
 
-	return pwrite_in_full(q->fd, c->table, size * sizeof(u64), c->offset);
+	if (pwrite_in_full(q->fd, c->table, size * sizeof(u64), c->offset) < 0)
+		return -1;
+
+	c->dirty = 0;
+
+	return 0;
 }
 
 static int cache_table(struct qcow *q, struct qcow_l2_table *c)
@@ -447,6 +455,7 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
 	if (!clust_start) {
 		clust_start		= ALIGN(f_sz, clust_sz);
 		l2t->table[l2t_idx]	= cpu_to_be64(clust_start);
+		l2t->dirty		= 1;
 	}
 
 	mutex_unlock(&q->mutex);
diff --git a/tools/kvm/include/kvm/qcow.h b/tools/kvm/include/kvm/qcow.h
index d44c64a..650d3c2 100644
--- a/tools/kvm/include/kvm/qcow.h
+++ b/tools/kvm/include/kvm/qcow.h
@@ -27,6 +27,7 @@ struct qcow_l2_table {
 	u64                     offset;
 	struct rb_node          node;
 	struct list_head        list;
+	u8			dirty;
 	u64                     table[];
 };
 
-- 
1.7.0.4