Hi,
I am working on a virtual disk driver and found that
The NT cache manager at times deadlocks, if I use filesystem that uses
cache manager on the virtual disk and the virtual ndisk itself is stored
on a filesystem that also uses cache manager.
To avoid the deadlock I use FILE_NO_INTERMEDIATE_BUFFERING while
creating/opening virtual disk file. However if the virtual disk file is
compressed/encrypted the system caches the virtual disk file anyway, so
the above solution does not work with compressed/encrypted virtual disk
file.
Does any budy has faced similar problem or is there a better solution
available for this problem?
Regards
Mohan
On Wed, 15 Jul 2009, Mohan Bisht wrote:
To avoid the deadlock I use FILE_NO_INTERMEDIATE_BUFFERING while
creating/opening virtual disk file. However if the virtual disk file is
compressed/encrypted the system caches the virtual disk file anyway, so
the above solution does not work with compressed/encrypted virtual disk
file.
Does any budy has faced similar problem or is there a better solution
available for this problem?
Yes that is a well known problem with virtual disks and the solution is to
not allow the image file to be compressed or encrypted (however I think
that the deadlock only ocur when writing so you coud allow read-only mode)
If you absolutly want the image file to be compressed you coud in theory
open it in raw mode and decompress it your self to a private buffer, the
functions needed is parhaps undocumented but still available on the net.
Bo Branten
Thanks Braten,
Yes, you are right. We faced the deadlocks only with write operations.
I think we will go with the approach of disallowing compression/encryption for the time being.
Regards
Mohan
-----Original Message-----
From: xxxxx@lists.osr.com [mailto:xxxxx@lists.osr.com] On Behalf Of Bo Brant?n
Sent: Wednesday, July 15, 2009 6:22 PM
To: Windows File Systems Devs Interest List
Subject: Re: [ntfsd] Virtual Disk Driver - Encryption/compression flag
On Wed, 15 Jul 2009, Mohan Bisht wrote:
To avoid the deadlock I use FILE_NO_INTERMEDIATE_BUFFERING while
creating/opening virtual disk file. However if the virtual disk file
is compressed/encrypted the system caches the virtual disk file
anyway, so the above solution does not work with compressed/encrypted
virtual disk file.
Does any budy has faced similar problem or is there a better solution
available for this problem?
Yes that is a well known problem with virtual disks and the solution is to not allow the image file to be compressed or encrypted (however I think that the deadlock only ocur when writing so you coud allow read-only mode)
If you absolutly want the image file to be compressed you coud in theory open it in raw mode and decompress it your self to a private buffer, the functions needed is parhaps undocumented but still available on the net.
Bo Branten
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