Re: How to force discarding of invalid cached partition contents?

Norman,

You might want to, before beginning the format sequence, obtain an exclusive
lock on the physical drive where the volume is located. Do, the format with
that handle, and then unlock to get the cache discarded. The open will
force any dirty cache blocks to disk before it grants you a handle.

"David Craig" <drivers@xxxxxxxxxx> wrote in message
news:ORJoVv85IHA.1420@xxxxxxxxxxxxxxxxxxxxxxx
In the last few weeks I posted some calling sequences on this newsgroup,
microsoft.public.win32.programmer.kernel, or ntdev that provide info on
how to do this. You could use IRP Tracker to see what chkdsk does when
the /F option is specified.

The format program I wrote uses the physical drive <number> to open the
entire drive and only puts on partition on the media. There is also a
format utility from linux that has been ported to windows as a command
line utility that also works. I have used it on a compact flash that is
used to load RTL code into a FPGA because the loader is really picky about
the file. I don't know if it is because it requires the file be
sequentially allocated or it requires the subdirectories be located in the
first entry.

"Norman Diamond" <ndiamond@xxxxxxxxxxxxxxxx> wrote in message
news:%23gybGd85IHA.192@xxxxxxxxxxxxxxxxxxxxxxx
A USB hard drive contains a FAT32 partition. Sometimes the partition has
a drive letter assigned. When the partition has a drive letter, Windows
Explorer and/or some other parts of Windows XP read and cache a portion of
the contents. I write part of the partition myself, so I want to force
Windows to abandon its cached contents.

I call DeviceIoControl several times. FSCTL_LOCK_VOLUME,
FSCTL_DISMOUNT_VOLUME, IOCTL_VOLUME_OFFLINE, IOCTL_VOLUME_ONLINE, and
FSCTL_UNLOCK_VOLUME. All of these succeed. WinIoCtl.h doesn't define
IOCTL_VOLUME_OFFLINE and IOCTL_VOLUME_ONLINE, but MSDN implies that these
are supposed to be available to user mode applications, so I define them
myself and DeviceIoControl reports success.

After that, I have found two ways to do manual operations to force
Windows to abandon its cached contents. One is to use Computer
Administrator - Disk Administrator, remove the drive letter from the
partition, and reassign the drive letter to the partition. The other way
is to open a command prompt and run CHKDSK /F, which finds no errors but
which somehow persuades Windows XP to discard its cache. If I omit the
/F then the obsolete contents remain in the cache, after which Windows
proceeds to corrupt the partition and then the next CHKDSK /F adjusts
errors (but lost data remain lost).

Now I want to do this programmatically. I wonder why obsolete contents
remain in the cache after IOCTL_VOLUME_OFFLINE and IOCTL_VOLUME_ONLINE,
but continue trying anyway. I added calls to BroadcastSystemMessage with
DBT_DEVICEREMOVECOMPLETE and DBT_DEVICEARRIVAL. These report success.
Furthermore if Windows Explorer was displaying the partition before these
operations, I can see Windows Explorer respond by removing that partition
from its display, displaying the contents of another partition, and then
restoring the drive letter and icon in the left hand pane though the
right hand pane continues displaying the other partition that it had
switched to. So I think that DBT_DEVICEREMOVECOMPLETE and
DBT_DEVICEARRIVAL have some amount of effect. But when I click on that
drive letter in Windows Explorer, it still displays obsolete cached
information, and creating a new file causes corruption in the partition.

What does it take to force Windows to discard obsolete cached data?




.

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