File system filter driver on network drives and IRP_NOCACHE

NTFSD
1

We are working on encryption file system filter driver for WinXP and NTFS.
We monitor the existence of flag IRP_NOCACHE in Irp->Flags and we
change/encrypt the data based on this flag - and this works on local disks.
But we have problem with network drives, where the behaviour is different.

On local drive the processing sequence is following:

  1. IRP_MJ_WRITE request without flag IRP_NOCACHE - now the data are only in
    cache, not yet on the disk.

  2. IRP_MJ_WRITE request with flags IRP_NOCACHE and IRP_PAGING_IO - now we
    change/encrypt data and sent them to lower driver(s).

While on network drive the sequence is:

  1. IRP_MJ_WRITE request without flag IRP_NOCACHE (same as for local drive) -
    now the data are after this request already physicaly on disk (not in
    cache).

  2. No other IRP_MJ_WRITE request appears :-((

Why the “same” write to local drive behave differently on network drive?

When we should change data? For the network scenario we have no chance …

2

I also would like to know how this works
on network FSs. Maybe the redirector has
disabled the file caching (see the article at OSR’s
web site about caching in the network file systems).

It would be good to explore the problem with my FileTest
tool. You can make an exactly targeted request to a
certain file, and watch the “other side” (the server)
if and when the request comes there.

You can download he tool from OSR online

L.

3

The redirector must first grab the oplock to allow the cache use. Maybe
sometimes this does not occur.

Maxim Shatskih, Windows DDK MVP
StorageCraft Corporation
xxxxx@storagecraft.com
http://www.storagecraft.com

----- Original Message -----
From: “Ladislav Zezula”
To: “Windows File Systems Devs Interest List”
Sent: Tuesday, February 08, 2005 3:38 PM
Subject: Re: [ntfsd] File system filter driver on network drives and
IRP_NOCACHE

> I also would like to know how this works
> on network FSs. Maybe the redirector has
> disabled the file caching (see the article at OSR’s
> web site about caching in the network file systems).
>
> It would be good to explore the problem with my FileTest
> tool. You can make an exactly targeted request to a
> certain file, and watch the “other side” (the server)
> if and when the request comes there.
>
> You can download he tool from OSR online
>
> L.
>
>
> —
> Questions? First check the IFS FAQ at
https://www.osronline.com/article.cfm?id=17
>
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