[PATCH 3/3] xen-blkback: make statistics data persistent across disconnect/connect

[Juergen Gross <jgross@suse.com>]

Today the statistics data is living in struct xen_blkif_ring only.

This means that a disconnect/connect cycle will reset the data, as the
rings are freed and re-allocated in this case.

Add a struct xen_blkif_stat in struct xen_blkif and sum up the per-ring
data there when freeing the rings, and add those values to the printed
statistics data.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 drivers/block/xen-blkback/common.h |  2 ++
 drivers/block/xen-blkback/xenbus.c | 19 ++++++++++++++++---
 2 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
index f8385c4b9d30..c35ec207b31d 100644
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -327,6 +327,8 @@ struct xen_blkif {
 	unsigned int		nr_rings;
 
 	unsigned long		buffer_squeeze_end;
+
+	struct xen_blkif_stat	st;
 };
 
 struct seg_buf {
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index b3ef483a92fd..f0d4cec4432a 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -346,6 +346,18 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 	 */
 	write_lock(&blkif->rings_lock);
 
+	for (r = 0; r < blkif->nr_rings; r++) {
+		struct xen_blkif_ring *ring = &blkif->rings[r];
+
+		blkif->st.rd_req += ring->st.rd_req;
+		blkif->st.wr_req += ring->st.wr_req;
+		blkif->st.oo_req += ring->st.oo_req;
+		blkif->st.f_req += ring->st.f_req;
+		blkif->st.ds_req += ring->st.ds_req;
+		blkif->st.rd_sect += ring->st.rd_sect;
+		blkif->st.wr_sect += ring->st.wr_sect;
+	}
+
 	rings = blkif->rings;
 	blkif->rings = NULL;
 	blkif->nr_rings = 0;
@@ -399,13 +411,14 @@ void xen_blkif_interface_fini(void)
 		struct backend_info *be = dev_get_drvdata(&dev->dev);	\
 		struct xen_blkif *blkif = be->blkif;			\
 		unsigned int i;						\
-		unsigned long long result = 0;				\
+		unsigned long long result;				\
 									\
 		read_lock(&blkif->rings_lock);				\
-		if (!blkif->rings)				\
+		result = blkif->st.name;				\
+		if (!blkif->rings)					\
 			goto out;					\
 									\
-		for (i = 0; i < blkif->nr_rings; i++) {		\
+		for (i = 0; i < blkif->nr_rings; i++) {			\
 			struct xen_blkif_ring *ring = &blkif->rings[i];	\
 									\
 			result += ring->st.name;			\
-- 
2.56.0