Getting RAS_LINKS info from C#

[libzhark]

I’m trying to extend the C# listadapters example to display information on WAN links, but the RAS_LINKS structure returned by GetRasLinks always has nNumberOfLinks of 0. I’m adding the following code inside the adapter loop, after it prints the adapter mode.

RAS_LINKS pLinks = new RAS_LINKS();

GCHandle.Alloc(pLinks);

Ndisapi.GetRasLinks(hNdisapi, AdList.m_nAdapterHandle, ref pLinks);

Console.WriteLine("RAS_LINKS:" + pLinks.nNumberOfLinks);

The C++ example returns the proper information on links when i plug in a 3g card, but from C# it always tells me nothing is there. To get this to run, I did have to change RAS_LINKS_MAX to 32 so that the runtime would stop complaining about too large a data structure to marshal, so maybe that has something to do with it?

[Vadim Smirnov]

When driver receives the memory block it checks if it has the correct size before filling it with data. If you shrinked the RAS_LINKS structure and passed smaller memory block to driver then it just has failed the operation. Is there a problem in C# with allocating large block of unmanaged memory?

[libzhark]

Yes, when calling the line

Ndisapi.GetRasLinks(hNdisapi, AdList.m_nAdapterHandle, ref pLinks);

an exception is thrown:

System.Runtime.InteropServices.MarshalDirectiveException: Cannot marshal 'parameter #3': Internal limitation: structure is too complex or too large.

This happens when RAS_LINKS_MAX = 256. From quick googling, it appears there is a hard 64k (65535 byte) limit for marshaling a single chunk of data.

[libzhark]

Ok, got it working. Need to change the declaration of GetRasLinks to:

[DllImport("ndisapi.dll")]

public static extern bool GetRasLinks(IntPtr hOpen, IntPtr hAdapter, IntPtr pLinks);

And then you can call it via:

IntPtr data = Marshal.AllocHGlobal(Marshal.SizeOf(typeof(RAS_LINKS)));

Ndisapi.GetRasLinks(hNdisapi, AdList.m_nAdapterHandle, data);

RAS_LINKS RasLinks = (RAS_LINKS)Marshal.PtrToStructure(data, typeof(RAS_LINKS));

Console.WriteLine("RAS_LINKS:" + RasLinks.nNumberOfLinks);

[Vadim Smirnov]

Thank you for the information. We will change declaration of GetRasLinks for the next release.

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