Wouldn’t a function like **CreateFile that accepts target device
object (so you can send it to the device’s beneath you instead of tossing it
up in the air and letting it land on your head) be useful for filter driver
writers? I’ve considered writing one, but rolling my own IRP_MJ_CREATE
sounds nightmarish. If anyone knows of any public documentation on how to
create your own IRP_MJ_CREATE - I’d like to look at it. It would be
instructional, if nothing else.
-Joel
-----Original Message-----
From: Tony Mason [mailto:xxxxx@osr.com]
Sent: Wednesday, July 12, 2000 2:36 PM
To: File Systems Developers
Subject: [ntfsd] RE: preventing recursive loop in create dispatch hand ler
Marc,
The general problem with such approaches is that they “work” until you begin
to deal with interactions involving other filter drivers, when any change in
thread context will cause you to deadlock (because the mutex is not
available, the second thread blocks. The first thread waits for the second
thread to finish.) This is a problem that can occur when someone else’s
filter is using handles (and thus switches to a known thread context) or
uses captive threads (in a user service, or even system threads.)
Regards,
Tony Mason
Consulting Partner
OSR Open Systems Resources, Inc.
http://www.osr.com http:
-----Original Message-----
From: Marc Sherman [mailto:xxxxx@bionetrix.com]
Sent: Wednesday, July 12, 2000 2:32 PM
To: File Systems Developers
Subject: [ntfsd] RE: preventing recursive loop in create dispatch hand ler
Before calling ZWCreateFile, aquire a mutex, then check to see if you’ve
aquired it recursively (mutex.Header.SignalState < 0). If this is true, your
hadling the irp that resulted from your ZWCreateFile. Release the mutex and
return. Remember to release your mutex after your ZWClose as well. This
works for one of our filters.
good luck,
Marc
-----Original Message-----
From: Smith, Joel [mailto:xxxxx@ntpsoftware.com]
Sent: Wednesday, July 12, 2000 2:21 PM
To: File Systems Developers
Subject: [ntfsd] RE: preventing recursive loop in create dispatch hand ler
Thanks,
In my case, though, I need to open the file before the file system
because it is important that I know the file’s size (if the file exists),
and, of course, a create might change the file’s size (overwrite,
superceded, etc). I suppose I could backup to the parent directory and do a
directory query for the file in question to determine its size. Then again,
I wonder if FsRtlGetFileSize is smart enough to work with a FILE_OBJECT that
has not been opened yet? Anyway, I’d still be interested in answers to my
original question because just recognizing a recursive open may be simpler
than solving the problem another way (like I mention above).
Thanks,
Joel
-----Original Message-----
From: Pavel Hrdina [mailto:xxxxx@sodatsw.cz mailto:xxxxx]
Sent: Wednesday, July 12, 2000 2:09 PM
To: File Systems Developers
Subject: [ntfsd] RE: preventing recursive loop in create dispatch handler
The best solution is to let the FSD to process the desired open first
and then you can read from the file. You do not need to close it because
you’re using the same file object as the successful requestor of this create
request.
Paul
> -----P?vodn? zpr?va-----
> Od: Smith, Joel [SMTP:xxxxx@ntpsoftware.com]
> Odesl?no: 12. ?ervence 2000 20:00
> Komu: File Systems Developers
> P?edm?t: [ntfsd] preventing recursive loop in create dispatch handler
>
> Hello,
> I know this has been asked before, and I apologize for asking
> again, but…
> Can anyone suggest a good way to prevent a recursive loop when
> opening the destination file for a create in the create dispatch routine.
>
> for example:
>
> CreateDisptachHandler(device, irp)
> {
> -ZwCreateFile(target of create) - this will cause a
> recursive loop, obviously
>
> -read some settings from file if it exists
>
> -ZwClose(target of create)
> }
>
> I believe there is a ‘well known’ solution to this problem, but I
> don’t know it.
>
> Thanks,
> Joel
>
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