File System and File System Filter Ecosystem Update

Neal ChristiansenDevelopment Lead

File System Filter Team

BOOT.INI and Longhorn The boot.ini file is no longer used to

configure boot parameters. New BCD (boot configuration data) file

Implemented as a registry hive Resides in \boot\bcd

There is a new tool called bcdedit which is used to configure options

Boot.ini is still used for downlevel operating systems if you are booting multiple OS’s on the same system

Useful bcdedit commands bcdedit –enum

List current settings bcdedit –enum all

List all settings bcdedit /?

Basic help bcdedit /? Types

Lists the bulk of the settings

Useful bcdedit commands

Enable debugging bcdedit -debug on Followed by one of the following:

bcdedit -dbgsettings serial debugport:1 baudrate:115200

bcdedit -dbgsettings 1394 CHANNEL:32 bcdedit –dbgsettings USB

TARGETNAME=U1

Doing IO from Completion Routines

Many of you issue IO operations from IO Completion routines (or post-operation callbacks) when those routines are at an IRQL level lower then DPC level

Filter manager promoted this with routines like FltDoCompletionProcessingWhenSafe

Doing IO from Completion Routines We have determined that it is not safe to ever perform any operation in a completion (or post-operation) callback routine regardless of your current IRQL level

We have been seeing deadlock with various storage drivers because of this The most common scenario we have seen is

when using dynamic disks with RAID enabled We have seen it with other drivers as well

Consider this a new “rule for filters”

Doing IO from Completion Routines It is our very strong recommendation

that you modify your existing products across all OS’s to stop doing this

You have two options: If the operation is synchronous you should

synchronize back to your dispatch routine Use IoIsOperationSynchronous

If the operation is asynchronous you should queue the request to a worker thread

You may have to throttle your worker thread usage because you can cause deadlocks if you consume all of the worker threads

Doing IO from Completion Routines What is filter manager going to do about

this? FltDoCompletionProcessingWhenSafe will be

modified to either queue the request or automatically synchronize and call the specified routine.

This will happen automatically so if you use the current routine you should not have to change anything

We are going to modify the minifilter verifier to detect this situation and break