Re: [ros-dev] [ros-diffs] 01/01: [NULL] Additions for the Null driver.

[Thomas Faber]

On 2018-04-22 22:23, Hermès Bélusca-Maïto wrote:
> diff --git a/drivers/base/null/null.c b/drivers/base/null/null.c
> index 610e886ddd..0d4ed541de 100644
> --- a/drivers/base/null/null.c
> +++ b/drivers/base/null/null.c
> @@ -181,26 +199,16 @@ DriverEntry(IN PDRIVER_OBJECT DriverObject,
>       DriverObject->MajorFunction[IRP_MJ_READ] = NullDispatch;
>       DriverObject->MajorFunction[IRP_MJ_LOCK_CONTROL] = NullDispatch;
>       DriverObject->MajorFunction[IRP_MJ_QUERY_INFORMATION] = NullDispatch;
> DriverObject->DriverUnload = NullUnload;
> /* Allocate the fast I/O dispatch table */
> FastIoDispatch = ExAllocatePoolWithTag(NonPagedPool,
>                                       sizeof(FAST_IO_DISPATCH),
>                                       'llun');
> if (!FastIoDispatch)
> {
>    /* Failed, cleanup */
>    IoDeleteDevice(DeviceObject);
>    return STATUS_INSUFFICIENT_RESOURCES;
> }
> /* Initialize it */
> RtlZeroMemory(FastIoDispatch, sizeof(FAST_IO_DISPATCH));
> FastIoDispatch->SizeOfFastIoDispatch = sizeof(FAST_IO_DISPATCH);
>
> /* Initialize the fast I/O dispatch table */
>
> RtlZeroMemory(&FastIoDispatch, sizeof(FastIoDispatch));
>
> FastIoDispatch.SizeOfFastIoDispatch = sizeof(FastIoDispatch);
>
> /* Setup our pointers */
> FastIoDispatch->FastIoRead = NullRead;
> FastIoDispatch->FastIoWrite = NullWrite;
> DriverObject->FastIoDispatch = FastIoDispatch;
> FastIoDispatch.FastIoRead = NullRead;
> FastIoDispatch.FastIoWrite = NullWrite;
> DriverObject->FastIoDispatch = &FastIoDispatch;

Are you sure FAST_IO_DISPATCH is allowed to be pageable? It seems to
only be used at low IRQLs, so it seems logical. However I see it
allocated nonpaged everywhere else and can't seem to find definitive
documentation on the subject.
(And yes, most filesystem drivers use a static structure, but those
  drivers don't use MmPageEntireDriver)

Thanks,
Thomas

[Ged Murphy]

They're pagable in NT6, I don't know whether that's the case in NT5.

Change looks good to me, I'm not really sure why Alex used NNP? 
Perhaps our kernel does/did things slightly differently back when he wrote the Null driver?

Ged.

-----Original Message-----
From: Ros-dev [e-mail] On Behalf Of Thomas Faber
Sent: Monday, 23 April 2018 07:49
To: Hermès Bélusca-Maïto [e-mail]
Cc: [e-mail]
Subject: Re: [ros-dev] [ros-diffs] 01/01: [NULL] Additions for the Null driver.

On 2018-04-22 22:23, Hermès Bélusca-Maïto wrote:
> diff --git a/drivers/base/null/null.c b/drivers/base/null/null.c index 
> 610e886ddd..0d4ed541de 100644
> --- a/drivers/base/null/null.c
> +++ b/drivers/base/null/null.c
> @@ -181,26 +199,16 @@ DriverEntry(IN PDRIVER_OBJECT DriverObject,
>       DriverObject->MajorFunction[IRP_MJ_READ] = NullDispatch;
>       DriverObject->MajorFunction[IRP_MJ_LOCK_CONTROL] = NullDispatch;
>       DriverObject->MajorFunction[IRP_MJ_QUERY_INFORMATION] = 
> NullDispatch;
> DriverObject->DriverUnload = NullUnload;
> /* Allocate the fast I/O dispatch table */
> FastIoDispatch = ExAllocatePoolWithTag(NonPagedPool,
>                                       sizeof(FAST_IO_DISPATCH),
>                                       'llun');
> if (!FastIoDispatch)
> {
>    /* Failed, cleanup */
>    IoDeleteDevice(DeviceObject);
>    return STATUS_INSUFFICIENT_RESOURCES;
> }
> /* Initialize it */
> RtlZeroMemory(FastIoDispatch, sizeof(FAST_IO_DISPATCH));
> FastIoDispatch->SizeOfFastIoDispatch = sizeof(FAST_IO_DISPATCH);
>
> /* Initialize the fast I/O dispatch table */
>
> RtlZeroMemory(&FastIoDispatch, sizeof(FastIoDispatch));
>
> FastIoDispatch.SizeOfFastIoDispatch = sizeof(FastIoDispatch);
>
> /* Setup our pointers */
> FastIoDispatch->FastIoRead = NullRead;
> FastIoDispatch->FastIoWrite = NullWrite;
> DriverObject->FastIoDispatch = FastIoDispatch;
> FastIoDispatch.FastIoRead = NullRead;
> FastIoDispatch.FastIoWrite = NullWrite;
> DriverObject->FastIoDispatch = &FastIoDispatch;

Are you sure FAST_IO_DISPATCH is allowed to be pageable? It seems to only be used at low IRQLs, so it seems logical. However I see it allocated nonpaged everywhere else and can't seem to find definitive documentation on the subject.
(And yes, most filesystem drivers use a static structure, but those
  drivers don't use MmPageEntireDriver)

Thanks,
Thomas

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