snmp plugin: Improve subtree matching.

Some MIBs use subtrees with an unusual OID naming schema. For example,
some network hardware encodes the MAC address in the last six parts of
the OID. Previously, the code only checked the last part of the OID
("sub-id") and assumed this was increasing. This assumption is not true
in such naming schemas and is not required by SNMP. This patch fixes
this behavior by comparing the entire "OID suffix".

This hopefully fixes Github issue #131.

diff --git a/src/snmp.c b/src/snmp.c
index 45d13c7..e265ae0 100644 (file)
--- a/src/snmp.c
+++ b/src/snmp.c
@@ -1,6 +1,6 @@
 /**
  * collectd - src/snmp.c
- * Copyright (C) 2007  Florian octo Forster
+ * Copyright (C) 2007-2012  Florian octo Forster
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -16,7 +16,7 @@
  * 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  *
  * Authors:
- *   Florian octo Forster <octo at verplant.org>
+ *   Florian octo Forster <octo at collectd.org>
  **/
 
 #include "collectd.h"
@@ -79,7 +79,7 @@ typedef struct host_definition_s host_definition_t;
  * gaps in tables. */
 struct csnmp_list_instances_s
 {
-  oid subid;
+  oid_t suffix;
   char instance[DATA_MAX_NAME_LEN];
   struct csnmp_list_instances_s *next;
 };
@@ -87,7 +87,7 @@ typedef struct csnmp_list_instances_s csnmp_list_instances_t;
 
 struct csnmp_table_values_s
 {
-  oid subid;
+  oid_t suffix;
   value_t value;
   struct csnmp_table_values_s *next;
 };
@@ -106,6 +106,54 @@ static int csnmp_read_host (user_data_t *ud);
 /*
  * Private functions
  */
+static void csnmp_oid_init (oid_t *dst, oid const *src, size_t n)
+{
+  assert (n <= STATIC_ARRAY_LEN (dst->oid));
+  memcpy (dst->oid, src, sizeof (*src) * n);
+  dst->oid_len = n;
+}
+
+static int csnmp_oid_compare (oid_t const *left, oid_t const *right)
+{
+  return (snmp_oid_compare (left->oid, left->oid_len,
+        right->oid, right->oid_len));
+}
+
+static int csnmp_oid_suffix (oid_t *dst, oid_t const *src,
+    oid_t const *root)
+{
+  /* Make sure "src" is in "root"s subtree. */
+  if (src->oid_len >= root->oid_len)
+    return (EINVAL);
+  if (snmp_oid_ncompare (root->oid, root->oid_len,
+        src->oid, src->oid_len,
+        /* n = */ root->oid_len) != 0)
+    return (EINVAL);
+
+  memset (dst, 0, sizeof (*dst));
+  dst->oid_len = src->oid_len - root->oid_len;
+  memcpy (dst->oid, &src->oid[root->oid_len],
+      dst->oid_len * sizeof (dst->oid[0]));
+  return (0);
+}
+
+static int csnmp_oid_to_string (char *buffer, size_t buffer_size,
+    oid_t const *o)
+{
+  char oid_str[MAX_OID_LEN][16];
+  char *oid_str_ptr[MAX_OID_LEN];
+  size_t i;
+
+  for (i = 0; i < o->oid_len; i++)
+  {
+    ssnprintf (oid_str[i], sizeof (oid_str[i]), "%lu", (unsigned long) o->oid[i]);
+    oid_str_ptr[i] = oid_str[i];
+  }
+
+  return (strjoin (buffer, buffer_size,
+        oid_str_ptr, o->oid_len, /* separator = */ "."));
+}
+
 static void csnmp_host_close_session (host_definition_t *host) /* {{{ */
 {
   if (host->sess_handle == NULL)
@@ -996,10 +1044,12 @@ static int csnmp_strvbcopy (char *dst, /* {{{ */
 
 static int csnmp_instance_list_add (csnmp_list_instances_t **head,
     csnmp_list_instances_t **tail,
-    const struct snmp_pdu *res)
+    struct snmp_pdu const *res,
+    oid_t const *root)
 {
   csnmp_list_instances_t *il;
   struct variable_list *vb;
+  oid_t vb_name;
 
   /* Set vb on the last variable */
   for (vb = res->variables;
@@ -1009,14 +1059,15 @@ static int csnmp_instance_list_add (csnmp_list_instances_t **head,
   if (vb == NULL)
     return (-1);
 
+  csnmp_oid_init (&vb_name, vb->name, vb->name_length);
+
   il = malloc (sizeof (*il));
   if (il == NULL)
   {
     ERROR ("snmp plugin: malloc failed.");
     return (-1);
   }
-  /* XXX copy entire OID */
-  il->subid = vb->name[vb->name_length - 1];
+  csnmp_oid_suffix (&il->suffix, &vb_name, root);
   il->next = NULL;
 
   /* Get instance name */
@@ -1064,8 +1115,8 @@ static int csnmp_dispatch_table (host_definition_t *host, data_definition_t *dat
   csnmp_table_values_t **value_table_ptr;
 
   int i;
-  oid subid;
-  int have_more;
+  _Bool have_more;
+  oid_t current_suffix;
 
   ds = plugin_get_ds (data->type);
   if (!ds)
@@ -1098,49 +1149,61 @@ static int csnmp_dispatch_table (host_definition_t *host, data_definition_t *dat
 
   vl.interval = host->interval;
 
-  subid = 0;
   have_more = 1;
-
-  while (have_more != 0)
+  memset (&current_suffix, 0, sizeof (current_suffix));
+  while (have_more)
   {
+    _Bool suffix_skipped = 0;
+
+    /* Determine next suffix to handle. */
     if (instance_list != NULL)
     {
-      while ((instance_list_ptr != NULL)
-         && (instance_list_ptr->subid < subid))
-       instance_list_ptr = instance_list_ptr->next;
-
+      instance_list_ptr = instance_list_ptr->next;
       if (instance_list_ptr == NULL)
       {
         have_more = 0;
         continue;
       }
-      else if (instance_list_ptr->subid > subid)
+
+      memcpy (&current_suffix, &instance_list_ptr->suffix, sizeof (current_suffix));
+    }
+    else /* no instance configured */
+    {
+      csnmp_table_values_t *ptr = value_table_ptr[0];
+      ptr = ptr->next;
+      if (ptr == NULL)
       {
-       subid = instance_list_ptr->subid;
+        have_more = 0;
         continue;
       }
-    } /* if (instance_list != NULL) */
 
+      memcpy (&current_suffix, &ptr->suffix, sizeof (current_suffix));
+    }
+
+    /* Update all the value_table_ptr to point at the entry with the same
+     * trailing partial OID */
     for (i = 0; i < data->values_len; i++)
     {
       while ((value_table_ptr[i] != NULL)
-         && (value_table_ptr[i]->subid < subid))
-       value_table_ptr[i] = value_table_ptr[i]->next;
+          && (csnmp_oid_compare (&value_table_ptr[i]->suffix, &current_suffix) < 0))
+        value_table_ptr[i] = value_table_ptr[i]->next;
 
       if (value_table_ptr[i] == NULL)
       {
         have_more = 0;
         break;
       }
-      else if (value_table_ptr[i]->subid > subid)
+      else if (csnmp_oid_compare (&value_table_ptr[i]->suffix, &current_suffix) > 0)
       {
-       subid = value_table_ptr[i]->subid;
+        /* This suffix is missing in the subtree. Indicate this with the
+         * "suffix_skipped" flag and try the next instance / suffix. */
+        suffix_skipped = 1;
         break;
       }
     } /* for (i = 0; i < columns; i++) */
-    /* The subid has been increased - start scanning from the beginning
-     * again.. */
-    if (i < data->values_len)
+
+    /* Matching the values failed. Start from the beginning again. */
+    if (!have_more || suffix_skipped)
       continue;
 
     /* if we reach this line, all value_table_ptr[i] are non-NULL and are set
@@ -1150,10 +1213,12 @@ static int csnmp_dispatch_table (host_definition_t *host, data_definition_t *dat
     for (i = 1; i < data->values_len; i++)
     {
       assert (value_table_ptr[i] != NULL);
-      assert (value_table_ptr[i-1]->subid == value_table_ptr[i]->subid);
+      assert (csnmp_oid_compare (&value_table_ptr[i-1]->suffix,
+            &value_table_ptr[i]->suffix) == 0);
     }
     assert ((instance_list_ptr == NULL)
-       || (instance_list_ptr->subid == value_table_ptr[0]->subid));
+        || (csnmp_oid_compare (&instance_list_ptr->suffix,
+            &value_table_ptr[0]->suffix) == 0));
 #endif
 
     sstrncpy (vl.type, data->type, sizeof (vl.type));
@@ -1162,7 +1227,7 @@ static int csnmp_dispatch_table (host_definition_t *host, data_definition_t *dat
       char temp[DATA_MAX_NAME_LEN];
 
       if (instance_list_ptr == NULL)
-       ssnprintf (temp, sizeof (temp), "%"PRIu32, (uint32_t) subid);
+        csnmp_oid_to_string (temp, sizeof (temp), &current_suffix);
       else
         sstrncpy (temp, instance_list_ptr->instance, sizeof (temp));
 
@@ -1178,9 +1243,7 @@ static int csnmp_dispatch_table (host_definition_t *host, data_definition_t *dat
 
     /* If we get here `vl.type_instance' and all `vl.values' have been set */
     plugin_dispatch_values (&vl);
-
-    subid++;
-  } /* while (have_more != 0) */
+  } /* while (have_more) */
 
   sfree (vl.values);
   sfree (value_table_ptr);
@@ -1344,7 +1407,8 @@ static int csnmp_read_table (host_definition_t *host, data_definition_t *data)
         /* do nothing */;
       assert (vb != NULL);
 
-      /* Copy the OID of the instance value to oid_list[data->values_len] */
+      /* Copy the OID of the instance value to oid_list[data->values_len].
+       * "oid_list" is used for the next GETNEXT request. */
       memcpy (oid_list[data->values_len].oid, vb->name,
           sizeof (oid) * vb->name_length);
       oid_list[data->values_len].oid_len = vb->name_length;
@@ -1358,6 +1422,9 @@ static int csnmp_read_table (host_definition_t *host, data_definition_t *data)
         vb = vb->next_variable, i++)
     {
       csnmp_table_values_t *vt;
+      oid_t vb_name;
+
+      csnmp_oid_init (&vb_name, vb->name, vb->name_length);
 
       /* Check if we left the subtree */
       if (snmp_oid_ncompare (data->values[i].oid,
@@ -1370,8 +1437,10 @@ static int csnmp_read_table (host_definition_t *host, data_definition_t *data)
         continue;
       }
 
+      /* Make sure the OIDs returned by the agent are increasing. Otherwise our
+       * table matching algorithm will get confused. */
       if ((value_list_tail[i] != NULL)
-         && (vb->name[vb->name_length - 1] <= value_list_tail[i]->subid))
+          && (csnmp_oid_compare (&vb_name, &value_list_tail[i]->suffix) <= 0))
       {
         DEBUG ("snmp plugin: host = %s; data = %s; i = %i; "
             "SUBID is not increasing.",
@@ -1379,15 +1448,16 @@ static int csnmp_read_table (host_definition_t *host, data_definition_t *data)
         continue;
       }
 
-      vt = (csnmp_table_values_t *) malloc (sizeof (csnmp_table_values_t));
+      vt = malloc (sizeof (*vt));
       if (vt == NULL)
       {
         ERROR ("snmp plugin: malloc failed.");
         status = -1;
         break;
       }
+      memset (vt, 0, sizeof (*vt));
 
-      vt->subid = vb->name[vb->name_length - 1];
+      csnmp_oid_suffix (&vt->suffix, &vb_name, data->values + i);
       vt->value = csnmp_value_list_to_value (vb, ds->ds[i].type,
           data->scale, data->shift);
       vt->next = NULL;