Sun Cluster Data Services Developer's Guide for Solaris OS

The `Validate` Method

The Validate method of a resource type implementation is called by the RGM in two scenarios: 1) when a new resource of the resource type is being created, and 2) when a property of the resource or resource group is being updated. These two scenarios can be distinguished by the presence of the command line option -c (creation) or -u (update) passed to the Validate method of the resource.

The Validate method is called on each node of a set of nodes, where the set of nodes is defined by the value of the resource type property INIT_NODES. If INIT_NODES is set to RG_PRIMARIES, Validate is called on each node that can host (be a primary of) the resource group containing the resource. If INIT_NODES is set to RT_INSTALLED_NODES, Validate is called on each node where the resource type software is installed, typically all nodes in the cluster. The default value of INIT_NODES is RG_PRIMARIES (see rt_reg(4). At the point the Validate method is called, the RGM has not yet created the resource (in the case of creation callback) or has not yet applied the updated value(s) of the properties being updated (in the case of update callback). The purpose of the Validate callback method of a resource type implementation is to check that the proposed resource settings (as specified by the proposed property settings on the resource) are acceptable to the resource type.

Note –

If you are using local file systems managed by HAStoragePlus, you use the scds_hasp_check to check the state of the HAStoragePlus resource, This information is obtained from the state (online or otherwise) of all SUNW.HAStoragePlus(5) resources that the resource depends upon using Resource_dependencies or Resource_dependencies_weak system properties defined for the resource. .See scds_hasp_check(3HA) for a complete list of status codes returned from the scds_hasp_check call.

The DSDL function scds_initialize() takes care of these situations in the following manner:

In the case of resource creation, it parses the proposed resource properties, as passed on the command line. The proposed values of resource properties are thus available to the resource type developer as if the the resource were already created in the system.
In the case of resource or resource group update, the proposed values of the properties being updated by the administrator are read in from the command line, and the remaining properties (whose values are not being updated) are read in from Sun Cluster using the Resource Management API. A resource type developer using the DSDL need not concern himself with all these housekeeping tasks. The validation of a resource can be done as if all the properties of the resource were available to the developer.

Suppose the function that implements the validation of a resource's properties is called svc_validate() which uses the scds_get_name() family of functions to look at the property it is interested in validating. Assuming that an acceptable resource setting is represented by a 0 return code from this function, the Validate method of the resource type can thus be represented by the following code fragment:

int
main(int argc, char *argv[])
{
   scds_handle_t handle;
   int rc;

   if (scds_initialize(&handle, argc, argv)!= SCHA_ERR_NOERR) {
   return (1);   /* Initialization Error */
   }
   rc = svc_validate(handle);
   scds_close(&handle);
   return (rc);
}

The the validation function should also log the reason for the failure of the validation of resource. Leaving out that detail (see the next chapter for a more realistic treatment of a validation function), a simple example svc_validate() function can then be implemented as:

int
svc_validate(scds_handle_t handle)
{
   scha_str_array_t *confdirs;
   struct stat    statbuf;
   confdirs = scds_get_confdir_list(handle);
   if (stat(confdirs->str_array[0], &statbuf) == -1) {
   return (1);   /* Invalid resource property setting */
   }
   return (0);   /* Acceptable setting */
}

The resource type developer thus has to concern himself with only the implementation of the svc_validate() function. A typical example for a resource type implementation could be to ensure that an application configuration file named app.conf exists under the Confdir_list property. That can be conveniently implemented by a stat() system call on the appropriate pathname derived from the Confdir_list property.

The Validate Method

The `Validate` Method