CreateDeviceAccessInstance does not allow file sharing (?!)

Question

Hi everyone,

  I successfully communicate with a custom driver through CreateDeviceAccessInstance / IDeviceIoControl API.

But.. now I face the following issue:

Question #1

Is there a way to configure CreateDeviceAccessInstance so that underling file object is shared for r/w access (FILE_SHARE_READ | FILE_SHARE_WRITE) ?

My custom driver is a UMDF (filter driver). It is also accessed via the desktop through plain old CreateFile (with above sharing flags set on).

If I try to play with CreateDeviceAccessInstance() flags it has no effect on file sharing options.

I can confirm it also by registering to IQueueCallbackCreate::OnCreateFile() in my driver : IWDFIoRequest::GetCreateParameters(&options, &fileAttributes, &shareAccess);

Question #2

Is there a way to modify the CreateFile request in the driver (for instance in above-mentionned callback), or issue another create file (internal to the driver) request, which would set FILE_SHARE_READ | FILE_SHARE_WRITE on? I just see IWDFIoRequest::GetCreateParameters, but no way to set them..

Thanks in advance!!

Julien

Answer 1

Julien,

I will look into this for you.

Best Wishes - Eric

Answer 2

Hi Eric,

  thanks very much! If you need more detailed context (or less obscure explanation :) I can provide some!

Regards,

Julien

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Julien Racle

Answer 3

Julien,

Createfile supports a flag for ShareMode as well as DesiredAccess:

HANDLE WINAPI CreateFile(
  __in      LPCTSTR lpFileName,
  __in      DWORD dwDesiredAccess,
  __in      DWORD dwShareMode,
  __in_opt  LPSECURITY_ATTRIBUTES lpSecurityAttributes,
  __in      DWORD dwCreationDisposition,
  __in      DWORD dwFlagsAndAttributes,
  __in_opt  HANDLE hTemplateFile
);

However CreateDeviceAccessInstance has only desiredAccess:

 HRESULT WINAPI 
CreateDeviceAccessInstance( 
    _In_ REFIID riid, 
    _In_ LPCWSTR deviceInterfacePath, 
    _In_ DWORD desiredAccess, 
    _Outptr_ ICreateDeviceAccessAsync **createAsync 
    );

However what we recommend is that your device driver have an additional interface for your Metro style device app.  Please let me know if you have any questions.

Best Wishes - Eric

Answer 4

Hi Eric,

Thanks for your kind reply. Indeed I'd need a bit more explanation :

CreateDeviceAccessInstance() is the only way I have to access my UMDF filter driver from within the Metro app I'm developing. It indeed does not support file sharing mode. Now, the trouble is that the same driver is also accessed from desktop mode via existing apps, which all use CreateFile (with sharing flags ON). Those apps are on the field, already published and used by many people.

So I'm a bit puzzled : why no sharing option in CreateDeviceAccessInstance? Indeed, apart from my use case, multiple privileged metro apps are likely to access same device at the same time.

Is there a way to get around the issue by enforcing those flags, for instance in my driver's IQueueCallbackCreate::OnCreateFile(), so that I don't get a sharing violation error..

Thanks so much for investigating!
Julien

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Julien Racle

Answer 5

Eric,

  Again thanks for your answer. If no other way than creating another interface in my driver is found, I gonna try to do so.

BTW my filter driver also is on top of (your) HID class driver, and it forwards many IO requests, so I don't know how to do the relationship between both interfaces/file objects (HID and mine).

You may consider raising the issue for DWORD dwShareMode abscence in CreateDeviceAccessInstance() : indeed the problem will be now that 2 metro apps running in parallel (tiled for instance, or 1 app and a background task), will encounter same file sharing issue (hence option would be to create several interfaces in the diver?! ;).

Thanks!

Julien

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Julien Racle

Answer 6

Julien,

Is your driver a device filter or class filter?  I will raise the issue about the WinRT API.

Best Wishes - Eric

Answer 7

Hi Eric,

  this is a HID class filter driver installed over a HID vendor collection.

It already works, "except" this file sharing violation issue, which prevents multiple clients.

Best Regards,

Julien

---

Julien Racle

Answer 8

Julien,

I am looking into this for you. 

Best Wishes - Eric 

Answer 9

Julien,

A HID vendor collection does not use file sharing modes in its create path. Are you building this driver on top of a file system?  A file system driver is the only driver I am aware of that would need SharedMode.

Are you certain you need the share access in the desktop application?

Best Wishes - Eric

Answer 10

Hi Eric,

  no, my HID filter driver is built on top of HID class driver, not the filesystem.

I'm not sure to catch what you mean by "A HID vendor collection does not use file sharing modes in its create path.".

Indeed my legacy app uses CreateFile(.... FILE_SHARE_WRITE | FILE_SHARE_READ...) on top level collection's interface path.

If I remove this, then obviously it becomes single client.

Apps I have in the field already use file sharing option : they communicate via a single top level collection through HID class driver.

If I don't have share access in desktop, then it will :

1. break legacy support
2. break also device access sharing between metro apps / contracts / background tasks (imagine the pb when 2 apps are tiled, or 1 app is running and another needs a contract which also makes use of this device in question)

Best,

Julien

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Julien Racle

Answer 11

Julien,

For MDA access to HID devices it is recommended to write a HID function driver using UMDF or KMDF to avoid sharing conflicts.

Best Wishes - Eric

  

Answer 12

Sorry Eric, but that means I have to write HID class driver myself?

(I repeat : goal is to use HID class driver, and additionally provide shared access to custom features via a vendor collection).

We have dozens of thousands of devices (mice, keyboards) which work this way in my company actually on desktop side, and I would bet we won't plan to develop a function driver to replace HID class driver..

From my point of view, this sounds like a missing parameter in your API, isn't it?

Regards,

Julien

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Julien Racle

Answer 13

Julien,

I will continue to look into this.

Best Wishes - Eric

Answer 14

Thanks again very much Eric, and sorry for taking your bandwidth :)

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Julien Racle

Answer 15

You are very welcome Julien.  I appreciate the question.

Best Wishes - Eric

Answer 16

Julien,

We now have a sample of a HID function driver:

http://code.msdn.microsoft.com/windowshardware/HID-Client-Sample-2e2a6281

The function:

HRESULT WINAPI 
CreateDeviceAccessInstance( 
     _In_ REFIID riid, 
     _In_ LPCWSTR deviceInterfacePath, 
     _In_ DWORD desiredAccess, 
     _Outptr_ ICreateDeviceAccessAsync **createAsync 
     );

is not likely to have sharemode added to it.

Best Wishes - Eric

Answer 17

Hi Eric,

  thanks again for your reply. I'll try that out and hope it'll address my point!

Thanks very much!

---

Julien Racle

Answer 18

Julien,

You are very welcome.  Thank You!

Best Wishes - Eric