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

diff --git a/tools/xenstat/libxenstat/src/xenstat_linux.c b/tools/xenstat/libxenstat/src/xenstat_linux.c
index d6e2cf3fe03f4fa1ce1e2266db6dc38c38278645..46f8bb76dfecbb683a71122524b150d5e1170d7e 100644 (file)
--- 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));