You place the string Microsoft Windows Network in the lpProvider member of
the NETRESOURCE structure to start Services Monitor's enumeration process. The
WNetEnumResource function fills in the other structure values after it starts
enumeration. The dwScope, dwType, and dwUsage members of the NETRESOURCE
structure define the same information as the first three WNetOpenEnum
parameters. The dwDisplayType member provides additional information about a
resource's type; it reports whether network resources are domains, servers, or
shares. The lpLocalName member contains the names of any remapped local devices.
The lpRemoteName member contains the name of the network resource, and lpComment
contains a description of the resource. The WNetOpenEnum function uses its fifth
parameter to return an enumeration handle that the WNetEnumResource function
uses in subsequent calls.
At B, Listing 1 calls the WNetEnumResource function to enumerate the
network resources. The WNetEnumResource function takes four parameters.
The first parameter is the handle that the WNetOpenEnum function returns. The
second parameter identifies the number of entries the WNetEnumResource function
needs to return per call. The third parameter is a buffer that contains the
NETRESOURCE structure that the WNetEnumResource function returns. The fourth
parameter specifies the size of the third parameter's buffer.
The NETRESOURCE structure that the WNetEnumResource function returns is a
pointer. Listing 1's CopyMemory function copies the NETRESOURCE information from
the buffer pointer into a structure so that Services Monitor can use the
information in VB.
At C, Listing 1 uses the dwDisplayType member of the NETRESOURCE structure
to determine whether the resource is a domain, server, or shared disk or
printer. A VB Select statement then adds the structure information to the
collection for that type of resource. If the NETRESOURCE structure contains
domain information, the Select statement uses the structure information to
create a new CDomain object, then passes the structure information as a
parameter to the CDomain object's Init function. If the NETRESOURCE structure
contains server information, the Select statement creates a CServer object and
passes the structure information to the CServer class Init function. Services
Monitor uses the CDomain and CServer objects to display resource information in
the tree view. At D, Listing 1 uses the WNetCloseEnum function to close the
enumeration.
The same NETRESOURCE structures that Services Monitor uses to represent
domains can enumerate servers, the children of domains. After the
WNetEnumResource function enumerates a resource, the third parameter in the
calling list passes a pointer that identifies the NETRESOURCE structure to the
WNetOpenEnum function. The pointer tells the WNetOpenEnum function to move to
the next level of the hierarchy and open an enumeration for the resource's
children. Services Monitor uses the same functions and structures to enumerate
every level of the network resource hierarchy, so the WNetOpenEnum and
WNetEnumResource routines must be common code that works for all the hierarchy's
levels.
Listing Services
The NT SCM subsystem starts automatically when a system boots. The SCM reads
information from a database in the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services Registry key about two types of services: installed
services, such as the SQL Server or Workstation services, and driver
services, such as 4mmDAT and Atdisk (kernel and file system drivers). This
Registry key contains information about each service's security context, where
its executable is, whether it starts automatically or manually, whether its
failure is critical to the system, and the names of other services it depends
on. Services Monitor monitors only installed services, but you can alter the
code to also monitor driver services.
When a user expands a domain, Services Monitor retrieves a list of
installed services from every server in the domain. Listing 2 shows the code
that obtains the list of installed services for each remote server.
At A, Listing 2 uses the OpenSCManager API call to list a machine's
services. The OpenSCManager function takes three parameters. The first parameter
contains the server name that the WNetEnumResource function returns in Listing 1. The second parameter is a string that identifies the services database for Services Monitor to open. The value "ServicesActive" tells the OpenSCManager function to open the database of active services. The third parameter specifies the type of permissions Services Monitor needs to access the target machine's SCM database; the value SC_MANAGER_ENUMERATE_SERVICE
defines the access rights that Services Monitor needs. When the OpenSCManager function completes, it returns a handle that the EnumServicesStatus function uses to create a buffer of ENUM_SERVICE_STATUS structures.
At B, Listing 2 shows the EnumServicesStatus function, which takes eight
parameters. The first parameter is the handle the OpenSCManager function
returns. The second parameter is a constant that specifies the type of services
the EnumServicesStatus function needs to poll. The value SERVICE_WIN32 tells the
function to list installed services rather than driver services. The third
parameter further specifies the type of services the function returns. The value
SERVICE_STATE_ALL tells EnumServicesStatus to list both active and
inactive services.
The fourth parameter is the buffer in which EnumServicesStatus places an
array of the ENUM_SERVICE_STATUS structures the function returns. The
ENUM_SERVICE_STATUS structure is
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