libxenstat: Fix statistics for blktap disks on linux

Overview: update xenstat vbd statistics parsing from
/sys/devices/xen-backend to process blktap disks

Reason:
        -blktap devices (now referenced as tap rather than vbd in
        /sys) have statistics counters
        (e.g.,  rd_req, wr_req, oo_req) prepended by tap_
        -xenstat behavior did not previously account for this
        behavior, which resulted in 0 disks
        visible and similarly impacted disk statistics

To reproduce these conditions, make a domain with tap:aio backed disks
on 3.2.x, run xentop, and press B to view VBD stats (nothing will
appear for the domain using tap:aio)

Signed-off-by: steve.maresca@gmail.com

1 files changed, 19 insertions, 7 deletions

diff --git a/tools/xenstat/libxenstat/src/xenstat_linux.c b/tools/xenstat/libxenstat/src/xenstat_linux.c
index d6e2cf3fe0..46f8bb76df 100644
--- a/tools/xenstat/libxenstat/src/xenstat_linux.c
+++ b/tools/xenstat/libxenstat/src/xenstat_linux.c
@@ -181,6 +181,12 @@ int xenstat_collect_vbds(xenstat_node * node)
 	struct dirent *dp;
 	struct priv_data *priv = get_priv_data(node->handle);
 
+	char *sys_prefix = "statistics/";
+
+	/* 23 = "statistics/" + "xxxx_xx_req" */
+	char ooreq[23], rdreq[23], wrreq[23]; 
+	char *stat_prefix = NULL;
+
 	if (priv == NULL) {
 		perror("Allocation error");
 		return 0;
@@ -208,12 +214,16 @@ int xenstat_collect_vbds(xenstat_node * node)
 		if (ret != 3)
 			continue;
 
-		if (strcmp(buf,"vbd") == 0)
+
+		if (strcmp(buf,"vbd") == 0){
+			stat_prefix = "";
 			vbd.back_type = 1;
-		else if (strcmp(buf,"tap") == 0)
+		} else if (strcmp(buf,"tap") == 0){
+			stat_prefix = "tap_";
 			vbd.back_type = 2;
-		else
+		} else {
 			continue;
+		}
 
 		domain = xenstat_node_domain(node, domid);
 		if (domain == NULL) {
@@ -224,25 +234,27 @@ int xenstat_collect_vbds(xenstat_node * node)
 			continue;
 		}
 
-		if((read_attributes_vbd(dp->d_name, "statistics/oo_req", buf, 256)<=0)
+		snprintf(ooreq, sizeof(ooreq), "%s%soo_req", sys_prefix, stat_prefix);
+		if((read_attributes_vbd(dp->d_name, ooreq, buf, 256)<=0)
 		   || ((ret = sscanf(buf, "%llu", &vbd.oo_reqs)) != 1))
 		{
 			continue;
 		}
 
-		if((read_attributes_vbd(dp->d_name, "statistics/rd_req", buf, 256)<=0)
+		snprintf(rdreq,  sizeof(rdreq),"%s%srd_req", sys_prefix, stat_prefix);
+		if((read_attributes_vbd(dp->d_name, rdreq, buf, 256)<=0)
 		   || ((ret = sscanf(buf, "%llu", &vbd.rd_reqs)) != 1))
 		{
 			continue;
 		}
 
-		if((read_attributes_vbd(dp->d_name, "statistics/wr_req", buf, 256)<=0)
+		snprintf(wrreq,  sizeof(wrreq),"%s%swr_req", sys_prefix, stat_prefix);
+		if((read_attributes_vbd(dp->d_name, wrreq, buf, 256)<=0)
 		   || ((ret = sscanf(buf, "%llu", &vbd.wr_reqs)) != 1))
 		{
 			continue;
 		}
 
-
 		if (domain->vbds == NULL) {
 			domain->num_vbds = 1;
 			domain->vbds = malloc(sizeof(xenstat_vbd));