Why FltGetVolumeContext must be called at IRQL <= APC_LEVEL?

NTFSD
1

… I mean, I understand “why”, but why such restriction has been
chosen?
When my “post” routine is called at dispatch IRQL I need to check with
my “per-volume” context to see if I can complete it immediately or do I
need to do some work when it’s “safe”. Since I can’t get my volume
context in the “post” routine (because of raised IRQL) I need to pass it
as a parameter from “pre” operation even though I don’t need to pass to
“post” anything else. It’s not a big deal, but to my taste a bit “not so
clean” :slight_smile: After all (as I understood) VolumeContext maps to filter’s DO
in the “legacy” model. So, I assumed the context of “what can be
accessed at raised IRQL” would be preserved.

2

Volume contexts don’t map directly to a device object extension because
we don’t create a device object per mini-filter. We actually attach
them in a list. Unless your filter has more than one instance, I would
recommend you use instance contexts.

Volume and instance contexts could be made so you can do a “get” at DPC
level (in completion routines). I have filed a feature request to make
this change.

Neal Christiansen
Microsoft File System Filter Group Lead
This posting is provided “AS IS” with no warranties, and confers no
rights.

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Vladimir
Chtchetkine
Sent: Friday, March 26, 2004 5:24 PM
To: Windows File Systems Devs Interest List
Subject: [ntfsd] Why FltGetVolumeContext must be called at IRQL <=
APC_LEVEL?

… I mean, I understand “why”, but why such restriction has been
chosen?
When my “post” routine is called at dispatch IRQL I need to check with
my “per-volume” context to see if I can complete it immediately or do I
need to do some work when it’s “safe”. Since I can’t get my volume
context in the “post” routine (because of raised IRQL) I need to pass it
as a parameter from “pre” operation even though I don’t need to pass to
“post” anything else. It’s not a big deal, but to my taste a bit “not so
clean” :slight_smile: After all (as I understood) VolumeContext maps to filter’s DO
in the “legacy” model. So, I assumed the context of “what can be
accessed at raised IRQL” would be preserved.

Questions? First check the IFS FAQ at
https://www.osronline.com/article.cfm?id=17

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