FsContext use by non-PnP and non-FS driver

NTDEV
1

The doc for FILE_OBJECT only talks about FsContext for file system drivers and those with FDO (which I assume means a PnP driver). But what about WDM drivers that are neither file system nor PnP? This WDM sample driver uses FsContext to store its own data structure but it ASSERT's that FsContext is NULL before setting it. Can a top level driver that does not forward IRPs use FsContext with confidence that nothing else is using it or would use it?

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Your driver owns the fscontexts.

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Hi Marc,

Our plain WDM Audio driver (not based on WDF as the one in the samples) uses the FsContext2 field because when we tried to use the FsContext field it completly messed up the WDM Audio framework. In fact, the FsContext field is used by the WDM Audio framwork for own needs. So you can use the FsContext2 field which is available.

Regards,
Eric.

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Thanks Eric. I know nothing about the WDM Audio framework but it sounds (no pun intended) like your driver receives IRPs from other drivers and/or sends IRPs to other drivers. Is that right? Thanks!

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Marc,

In fact, for drivers, a lot of things are based on IRP. In our case, we need a dedicated context for side uses for the application level.

WDM Audio framework : https://learn.microsoft.com/en-us/windows-hardware/drivers/audio/windows-audio-architecture

Best regards,
Eric.

6
  • If your driver passes an IRP with FILE_OBJECT to another DEVICE_OBJECT (usually this is an underlying driver in the stack), your driver cannot use FsContext
  • If your driver completes IRP_MJ_CREATE requests and never pass an IRP with FILE_OBJECT to another DEVICE_OBJECT, your driver can use FsContext
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