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Question about read file

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#23357
Posted: 02/06/2013 10:40:17
by Davide Baccaglini (Standard support level)
Joined: 11/19/2012
Posts: 48

Hello, I've a question about read file.

Using ProcessMonitor I see that the operating system manages 2 type of reading events: IRP_MJ_READ and FASTIO_READ. With CBFS which type of event is managed?

Thanks in advance,
Davide
#23358
Posted: 02/06/2013 11:49:02
by Volodymyr Zinin (EldoS Corp.)

Both types are used. But the second one is "fast I/O" request. In order to accelerate I/O the system often sends it first to file systems. And if the file data is cached then the request finished quickly (in the case of CallbackFS it's processed internally by the driver without calling of the OnReadFile callback). In the other case the "fast I/O" request returns FALSE and Windows sends "usual" request (IRP_MJ_READ), which in the case of CallbackFS causes the OnReadFile callback is called.

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