Xen devel - Jun 2008 - [PATCH]: Fix libxenstat 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 )


Steve Maresca

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

diff -r b320cfe1f10f -r be6917832779
tools/xenstat/libxenstat/src/xenstat_linux.c
--- a/tools/xenstat/libxenstat/src/xenstat_linux.c    Thu Jun 05 13:04:07
2008 +0100
+++ b/tools/xenstat/libxenstat/src/xenstat_linux.c    Mon Jun 09 16:34:11
2008 -0400
@@ -181,6 +181,12 @@ int xenstat_collect_vbds(xenstat_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 *
         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
-            continue;
+        } else {
+            continue;
+        }

         domain = xenstat_node_domain(node, domid);
         if (domain == NULL) {
@@ -224,24 +234,26 @@ int xenstat_collect_vbds(xenstat_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;



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