What are "api-ms-win-*-*-lx-x-x.dll" umbrella libraries?

Question

I keep running into DLLs with long file names, as such. Just two for example: "api-ms-win-appmodel-runtime-l1-1-1.dll" or "api-ms-win-appmodel-identity-l1-2-0.dll". Evidently Microsoft calls them "umbrella libraries".

My original understanding was that they were just new DLLs with new file names, but then I tried to search for those files. Well, I couldn't find them as physical files on disk ...

So I'm curious, are they some sort of virtual DLL file names that don't exist on disk?

WCHAR buff[MAX_PATH];
buff[0] = 0;
GetSystemDirectory(buff, MAX_PATH);
StringCchCat(buff, MAX_PATH, L"\\api-ms-win-appmodel-runtime-l1-1-1.dll");

HMODULE hModule = LoadLibrary(buff);
//'hModule' is NULL & error code is ERROR_MOD_NOT_FOUND

But the following works:

HMODULE hModule = LoadLibrary(L"api-ms-win-appmodel-runtime-l1-1-1.dll");

Answer 1

this is “Virtual DLLs” names. loader, when we call LoadLibrary (LdrLoadDll) check for well known name prefix (say api- ) and if name begin with this - use ApiSetSchema mechanism for translate virtual dll name (i.e api-ms-win.. ) to real dll name (file name, like kernel32.dll, kernelbase.dll, etc). this mapping implemented in ApiSetSchema.dll which located in system32 folder.

about internal implementation - read Runtime DLL name resolution: ApiSetSchema - Part II and The API Set Schema