[XENSTAT] Ignore domains that are being created/destroyed during get_info call.

Currently, xenstat_get_node exits with a failure and returns NULL if a
VM is deleted between the time the list of VMs is obtained and the time
it attempts to collect information about the VMs. This patch modifies xenstat
to ignore domains that transition during the call.

Signed-off-by: Simon Graham <Simon.Graham@stratus.com>

1 files changed, 77 insertions, 22 deletions

diff --git a/tools/xenstat/libxenstat/src/xenstat.c b/tools/xenstat/libxenstat/src/xenstat.c
index 5d1f27f640..37a0e52b53 100644
--- a/tools/xenstat/libxenstat/src/xenstat.c
+++ b/tools/xenstat/libxenstat/src/xenstat.c
@@ -103,7 +103,10 @@ struct xenstat_vbd {
  * Data-collection types
  */
 /* Called to collect the information for the node and all the domains on
- * it. When called, the domain information has already been collected. */
+ * it. When called, the domain information has already been collected. 
+ * Return status is 0 if fatal error occurs, 1 for success. Collectors
+ * may prune a domain from the list if it has been deleted between the
+ * time the list was setup and the time the colector is called */
 typedef int (*xenstat_collect_func)(xenstat_node * node);
 /* Called to free the information collected by the collect function.  The free
  * function will only be called on a xenstat_node if that node includes
@@ -134,6 +137,7 @@ static void xenstat_uninit_networks(xenstat_handle * handle);
 static void xenstat_uninit_xen_version(xenstat_handle * handle);
 static void xenstat_uninit_vbds(xenstat_handle * handle);
 static char *xenstat_get_domain_name(xenstat_handle * handle, unsigned int domain_id);
+static void xenstat_prune_domain(xenstat_node *node, unsigned int entry);
 
 static xenstat_collector collectors[] = {
 	{ XENSTAT_VCPU, xenstat_collect_vcpus,
@@ -208,7 +212,7 @@ xenstat_node *xenstat_get_node(xenstat_handle * handle, unsigned int flags)
 	xenstat_node *node;
 	dom0_physinfo_t physinfo;
 	dom0_getdomaininfo_t domaininfo[DOMAIN_CHUNK_SIZE];
-	unsigned int num_domains, new_domains;
+	unsigned int new_domains;
 	unsigned int i;
 
 	/* Create the node */
@@ -242,15 +246,17 @@ xenstat_node *xenstat_get_node(xenstat_handle * handle, unsigned int flags)
 		return NULL;
 	}
 
-	num_domains = 0;
+	node->num_domains = 0;
 	do {
 		xenstat_domain *domain, *tmp;
 
 		new_domains = xc_domain_getinfolist(handle->xc_handle,
-			num_domains, DOMAIN_CHUNK_SIZE, domaininfo);
+						    node->num_domains, 
+						    DOMAIN_CHUNK_SIZE, 
+						    domaininfo);
 
 		tmp = realloc(node->domains,
-			      (num_domains + new_domains)
+			      (node->num_domains + new_domains)
 			      * sizeof(xenstat_domain));
 		if (tmp == NULL) {
 			free(node->domains);
@@ -259,12 +265,29 @@ xenstat_node *xenstat_get_node(xenstat_handle * handle, unsigned int flags)
 		}
 		node->domains = tmp;
 
-		domain = node->domains + num_domains;
+		domain = node->domains + node->num_domains;
+
+		/* zero out newly allocated memory in case error occurs below */
+		memset(domain, 0, new_domains * sizeof(xenstat_domain));
 
 		for (i = 0; i < new_domains; i++) {
 			/* Fill in domain using domaininfo[i] */
 			domain->id = domaininfo[i].domain;
-			domain->name = xenstat_get_domain_name(handle, domaininfo[i].domain);
+			domain->name = xenstat_get_domain_name(handle, 
+							       domain->id);
+			if (domain->name == NULL) {
+				if (errno == ENOMEM) {
+					/* fatal error */
+					xenstat_free_node(node);
+					return NULL;
+				}
+				else {
+					/* failed to get name -- this means the
+					   domain is being destroyed so simply
+					   ignore this entry */
+					continue;
+				}
+			}
 			domain->state = domaininfo[i].flags;
 			domain->cpu_ns = domaininfo[i].cpu_time;
 			domain->num_vcpus = (domaininfo[i].max_vcpu_id+1);
@@ -284,10 +307,9 @@ xenstat_node *xenstat_get_node(xenstat_handle * handle, unsigned int flags)
 			domain->vbds = NULL;
 
 			domain++;
+			node->num_domains++;
 		}
-		num_domains += new_domains;
 	} while (new_domains == DOMAIN_CHUNK_SIZE);
-	node->num_domains = num_domains;
 
 	/* Run all the extra data collectors requested */
 	node->flags = 0;
@@ -495,10 +517,12 @@ xenstat_vbd *xenstat_domain_vbd(xenstat_domain * domain,
 /* Collect information about VCPUs */
 static int xenstat_collect_vcpus(xenstat_node * node)
 {
-	unsigned int i, vcpu;
+	unsigned int i, vcpu, inc_index;
 
 	/* Fill in VCPU information */
-	for (i = 0; i < node->num_domains; i++) {
+	for (i = 0; i < node->num_domains; i+=inc_index) {
+		inc_index = 1; /* default is to increment to next domain */
+
 		node->domains[i].vcpus = malloc(node->domains[i].num_vcpus
 						* sizeof(xenstat_vcpu));
 		if (node->domains[i].vcpus == NULL)
@@ -509,11 +533,25 @@ static int xenstat_collect_vcpus(xenstat_node * node)
 			dom0_getvcpuinfo_t info;
 
 			if (xc_vcpu_getinfo(node->handle->xc_handle,
-				node->domains[i].id, vcpu, &info) != 0)
-				return 0;
-
-			node->domains[i].vcpus[vcpu].online = info.online;
-			node->domains[i].vcpus[vcpu].ns = info.cpu_time;
+					    node->domains[i].id, vcpu, &info) != 0) {
+				if (errno == ENOMEM) {
+					/* fatal error */ 
+					return 0;
+				}
+				else {
+					/* domain is in transition - remove
+					   from list */
+					xenstat_prune_domain(node, i);
+
+					/* remember not to increment index! */
+					inc_index = 0;
+					break;
+				}
+			}
+			else {
+				node->domains[i].vcpus[vcpu].online = info.online;
+				node->domains[i].vcpus[vcpu].ns = info.cpu_time;
+			}
 		}
 	}
 	return 1;
@@ -884,13 +922,30 @@ unsigned long long xenstat_vbd_wr_reqs(xenstat_vbd * vbd)
 static char *xenstat_get_domain_name(xenstat_handle *handle, unsigned int domain_id)
 {
 	char path[80];
-	char *name;
 
 	snprintf(path, sizeof(path),"/local/domain/%i/name", domain_id);
 	
-	name = xs_read(handle->xshandle, XBT_NULL, path, NULL);
-	if (name == NULL)
-		name = strdup(" ");
-
-	return name;
+	return xs_read(handle->xshandle, XBT_NULL, path, NULL);
 }	
+
+/* Remove specified entry from list of domains */
+static void xenstat_prune_domain(xenstat_node *node, unsigned int entry)
+{
+	/* nothing to do if array is empty or entry is beyond end */
+	if (node->num_domains == 0 || entry >= node->num_domains)
+		return;
+
+	/* decrement count of domains */
+	node->num_domains--;
+
+	/* shift entries following specified entry up by one */
+	if (entry < node->num_domains) {
+		xenstat_domain *domain = &node->domains[entry];
+		memmove(domain,domain+1,node->num_domains-entry);
+	}
+
+	/* zero out original last entry from node -- not
+	   strictly necessary but safer! */
+	memset(&node->domains[node->num_domains], 0, sizeof(xenstat_domain)); 
+}
+