Virtual volume driver

NTDEV
1

Hello,

I am writing a virtual device driver for mounting virtual volumes from files.
I started from the ramDisk example, but since then most of the code has changed (reads and writes are done with a worker thread and I can mount multiple volumes)

I still use the symbolic link trick so that windows will mount a file system and show the user a mount point (a drive letter)

I do intend to implement all of MountDev’s IOCTLs (and then there won’t be a need for the symbolic link) but for now it’s not a priority.

I have 100% functionality under XP, everything except for defrag etc as I’m not registered with mount dev, and this OK.

However under 7 I get the most peculiar bug, I can mount and format,copy files into/from my volume BUT I can’t rename or delete!

This is even weirder as I can say create a file with 1 meg of data and then open it and set its size to 0 kb, I simply can’t delete/rename it.

Has anyone seen windows behave in such an odd way?

(P.S. I am aware of the wonders of OSR’s Virtual Storport Miniport, but for reasons I can’t get into it was decided to go the path of the WDF driver)

Thanks in advance.

2

You need to provide more information.
How do you implement your driver? Where do you register it?

Igor Sharovar

3

Hi,
sorry for the delay…

the driver is a based on ramdisk (initially) but was changed so that:

  1. it’s not PnP, similar to the nopnp ddk example
  2. the way to create a device is no longer through the registry but through requests from user mode (ioctls) that create new instances.
  3. reads and writes are handled using a queue and a worker thread.
  4. after the instance is alive I create a symlink from it to \dosdevices\x:

when attempting to rename anything in 7 i get
“you need permission to perform this action You require permission for Administrator to make changes to this file”

Thanks

hope that helps

4

You likely need to change permissions to access to yours files. Click the right button of mouse on your file, choose Property/Security and modify permission in a group which you want to change.

Igor Sharovar

5

Hi, thanks for responding.

I’d try that, but this also happens on FAT formatted volumes that don’t have these kinds of security concerns.
Also on NTFS drives permissions look OK.

hjgi

6

> when attempting to rename anything in 7 i get

“you need permission to perform this action You require permission for Administrator to make changes to this file”

What about an ACL on your device object?

–
Maxim S. Shatskih
Windows DDK MVP
xxxxx@storagecraft.com
http://www.storagecraft.com

7

I tried:
SDDL_DEVOBJ_SYS_ALL_ADM_RWX_WORLD_RW_RES_R ,
SDDL_DEVOBJ_SYS_ALL_ADM_RWX_WORLD_RWX_RES_RWX ,
SDDL_DEVOBJ_SYS_ALL_ADM_RWX_WORLD_A

none helped, or even seemed to make any difference.

8

You don’t specify the factors involved in the decision, but maybe in hindsight a miniport was the better choice. You don’t need to implement any version sensitive, undocumented, or non-obvious code in a miniport for it to work right. There are no IOCTLs at all. The ramdisk sample is unfortunate since its existence causes people to select it and have a sub optimal solution. Just about anytime you need to create a storage device, a miniport is going to be the best, highest quality approach.

9

I do agree with, but in this was decided outside of my scope. So for now I have to try and make this work as best as possible.

So does anyone have any idea what I could be missing here?

10

Hi,

Well for posterity’s sake I?ll give the solution.
It seems that SDDL_DEVOBJ_SYS_ALL_ADM_RWX_WORLD_RWX_RES_RWX is not enough,
After giving it:
“D:P(A;;GA;;;SY)(A;;GA;;;BA)(A;;GA;;;WD)(A;;GA;;;RC)”
Everything works as expected…

Thanks anyway