Modifying ramdisk.sys sample to use PagedPool

NTDEV
1

Hi,

I need to modify Microsoft’s ramdisk.sys sample driver to support a
larger disk up to 64 megs. I figured that in this case it would be a
good idea to allocate the memory for the RAM disk from PagedPool instead
(the original sample allocates from NonPagedPool). So I’ve just changed
the memory allocation part in pnp.c to

// Allocate the memory for disk image.
//

devExt->DiskImage = ExAllocatePoolWithTag(
PagedPool,
devExt->DiskRegInfo.DiskSize,
RAMDISK_TAG_DISK);

and it seems to work. But I’m still a Greenhorn with respect to drivers
and would like to know if that’s indeed the only change I need to make
or if I’m asking for trouble.

Thanks!

Ralf.

2

You must make sure that your reads and writes are handled at
PASSIVE_LEVEL. You can do this with a system thread.

Jamey

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Ralf Buschmann
Sent: Tuesday, August 27, 2002 1:38 AM
To: NT Developers Interest List
Subject: [ntdev] Modifying ramdisk.sys sample to use PagedPool

Hi,

I need to modify Microsoft’s ramdisk.sys sample driver to support a
larger disk up to 64 megs. I figured that in this case it would be a
good idea to allocate the memory for the RAM disk from PagedPool instead
(the original sample allocates from NonPagedPool). So I’ve just changed
the memory allocation part in pnp.c to

// Allocate the memory for disk image.
//

devExt->DiskImage = ExAllocatePoolWithTag(
PagedPool,
devExt->DiskRegInfo.DiskSize,
RAMDISK_TAG_DISK);

and it seems to work. But I’m still a Greenhorn with respect to drivers
and would like to know if that’s indeed the only change I need to make
or if I’m asking for trouble.

Thanks!

Ralf.

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3

Jamey,

you wrote on Tuesday, August 27, 2002, 19:13:50:

RB>> // Allocate the memory for disk image.
RB>> //
RB>
RB>> devExt->DiskImage = ExAllocatePoolWithTag(
RB>> PagedPool,
RB>> devExt->DiskRegInfo.DiskSize,
RB>> RAMDISK_TAG_DISK);

JK> You must make sure that your reads and writes are handled at
JK> PASSIVE_LEVEL. You can do this with a system thread.

Thanks!

Let me ask another question: do I even need to make this change? My
system has 512 megs RAM and I could successfully use the original sample
(allocating from NonPagedPool) to create a 64 meg RAM disk. What are the
chances that there is not enough non paged memory available?

Ralf.

4

if that’s your concern you can always allocate paged pool and then lock
it down by calling MmProbeAndLockPages on the buffer. Just remember to
unlock before freeing it.

-p

-----Original Message-----
From: Ralf Buschmann [mailto:xxxxx@backmagic.de]
Sent: Tuesday, August 27, 2002 11:09 AM
To: NT Developers Interest List
Subject: [ntdev] RE: Modifying ramdisk.sys sample to use PagedPool

Jamey,

you wrote on Tuesday, August 27, 2002, 19:13:50:

RB>> // Allocate the memory for disk image.
RB>> //
RB>
RB>> devExt->DiskImage = ExAllocatePoolWithTag(
RB>> PagedPool,
RB>> devExt->DiskRegInfo.DiskSize,
RB>> RAMDISK_TAG_DISK);

JK> You must make sure that your reads and writes are handled at
JK> PASSIVE_LEVEL. You can do this with a system thread.

Thanks!

Let me ask another question: do I even need to make this change? My
system has 512 megs RAM and I could successfully use the original sample
(allocating from NonPagedPool) to create a 64 meg RAM disk. What are the
chances that there is not enough non paged memory available?

Ralf.

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