CODEWITHSUNDEEP
windowswinapipower-managementsleep-mode
jimc
jimc

Reputation: 149

Enumerate Windows "Power Availability Requests" with undocumented CallNtPowerInformation(GetPowerRequestList..)

Windows 7 introduced "Power Availability Requests". This feature allows applications to notify the OS that they require the display or whole system and therefore power management should be temporarily inhibited. The feature is documented here:

https://download.microsoft.com/download/7/E/7/7E7662CF-CBEA-470B-A97E-CE7CE0D98DC2/AvailabilityRequests.docx

The availability requests feature uses an object model and provides the functions PowerCreateRequest(), PowerSetRequest() and PowerClearRequest() to create requests, activate them and ultimately remove them. This functionality is very similar to the older SetThreadExecutionState() API available in Windows 2000 but allows multiple requests to be create per-thread and improves potential diagnostics by requiring each request to have a reason string.

The OS supplied POWERCFG.EXE utility can enumerate the current outstanding requests using the command:

POWERCFG -REQUESTS

Microsoft do not document how to enumerate requests with Windows API.

The CallNtPowerInformation() function in the SDK has been updated to support a new information level called "GetPowerRequestList". This looks very much like it could be the required API but is not documented.

Please does anyone know how to call CallNtPowerInformation(GetPowerRequestList..)?

Jim

Upvotes: 2

Views: 766

Answers (1)

vulture
vulture

Reputation: 21

Late answer, but, I found that it was easier to call this other function instead (since CallNtPowerInformation(GetPowerRequestList, ...) returned a not supported error):

PowerInformationWithPrivileges(GetPowerRequestList, 0, 0, bufout, 16384);

Function signature seemed to be the same, and you might have to define it and GetProcAddress from powrprof.dll yourself depending on what libs you have available.

Output format seemed to be a binary blob. If I had to guess, it's a list of int64's (even in 32-bit apps), first entry is # entries (call it x), next x entries are offsets in the blob for the real entries, which themselves are some kind of variable length blob/struct, probably correlating to each PowerRequest and/or type of request. Not complete info, but that should get other people started if they're serious about trying to make this work.

You need admin to call this function (you also need admin to call powercfg /requests, so this isn't too much of a surprise, though perhaps a shortcoming depending on your use case).

Upvotes: 2

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