PcwAddInstance function (wdm.h)

Article
01/13/2023

The PcwAddInstance function adds the specified instance of the counterset to the consumer buffer. Most developers will use a CTRPP-generated AddXxx function instead of calling this function directly. See Remarks below for more info.

Syntax

NTSTATUS PcwAddInstance(
  [in] PPCW_BUFFER      Buffer,
  [in] PCUNICODE_STRING Name,
  [in] ULONG            Id,
  [in] ULONG            Count,
  [in] PPCW_DATA        Data
);

Parameters

[in] Buffer

A handle to the system-managed buffer to which the instance of the counterset will be added. When the buffer comes from a PcwCallbackEnumerateInstances notification, PcwAddInstance will record only the Name and Id of the instance. When the buffer comes from a PcwCallbackCollectData notification, PcwAddInstance will record the Name, Id, and Data (counter values) of the instance.

[in] Name

A pointer to the Unicode string that contains the name of the counterset instance. This must not be NULL.

Instance Name values MUST be stable over time (the same logical instance should use the same Name value for all invocations of the callback) and MUST be unique. If the counterset is registered as single-instance, the instance Name should be blank (0-length). If the counterset registered as multi-instance, the instance Name should not be blank. Instance name matching is not case-sensitive, so Name values should not differ only by case.

[in] Id

A numeric value that specifies the Id (identifier) associated with the counterset instance.

Instance Id values MUST be stable over time (the same instance should use the same Id value for all invocations of the callback), should be unique (e.g. do not use 0 for all instances), and should be less than 0xFFFFFFFE (do not use PCW_ANY_INSTANCE_ID for any instances). When possible, the instance Id should be meaningful (e.g. a Process counterset might use a PID as the Id) instead of arbitrary (e.g. a sequence number).

[in] Count

The number of descriptors provided in the Data parameter.

[in] Data

An array of descriptors for the provider data blocks that contain the counter values of this instance.

Return value

PcwAddInstance returns one of the following values:

Return code	Description
`STATUS_SUCCESS`	The instance was successfully added to the buffer.
`STATUS_INVALID_BUFFER_SIZE`	One of the provider data blocks is too small. For example, suppose that during the call to PcwRegister, the provider specifies that counter `X` is at offset 100 of the first data block of size 4 bytes. If the call to `PcwAddInstance` specifies that the first data block is 50 bytes, this error status is returned.

Remarks

The PcwAddInstance function should called by the provider-defined PCW_CALLBACK routine when the notification type is either PcwCallbackEnumerateInstances or PcwCallbackCollectData. The Buffer to be used comes from the Info parameter for the PCW_CALLBACK routine, e.g. Info->EnumerateInstances.Buffer or Info->CollectData.Buffer.

When called for a PcwCallbackEnumerateInstances notification, PcwAddInstance adds the Name and Id values to the buffer. When called for a PcwCallbackCollectData notification, PcwAddInstance adds the Name, Id, and counter data values to the buffer.

CTRPP-generated Add*** function

Most developers do not need to call PcwAddInstance directly. Instead, they will compile a manifest with the CTRPP tool and use the Add*** function from the CTRPP-generated header. The generated function will look like this:

EXTERN_C __inline NTSTATUS
AddMyCounterset(
    __in PPCW_BUFFER Buffer,
    __in PCUNICODE_STRING Name,
    __in ULONG Id,
    __in_opt const MY_COUNTER_DATA *MyCounterData
    )
{
    PCW_DATA Data[1];

    PAGED_CODE();

    Data[0].Data = MyCounterData;
    Data[0].Size = sizeof(MY_COUNTER_DATA);

    return PcwAddInstance(Buffer,
                          Name,
                          Id,
                          1,
                          Data);
}

The CTRPP-generated Add function will be named PrefixAddCounterset. Prefix is usually blank, but may be present if the -prefix parameter was used on the CTRPP command-line. Counterset is the name of the counterset, as specified in the manifest. The function will have Data parameters based on the structures defined in the manifest. The function will wrap the user-provided data block(s) into an array of PCW_DATA structures and then call PcwAddInstance.

Requirements

Requirement	Value
Minimum supported client	Available in Windows 7 and later versions of Windows.
Target Platform	Universal
Header	wdm.h (include Wdm.h, Ntddk.h)
Library	NtosKrnl.lib
DLL	NtosKrnl.exe
IRQL	IRQL <= APC_LEVEL

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