How does Pismo File Mount mount ZIP files onto Windows Explorer?

Question

I have been using Pismo File Mount for many years, and I have always wondered how it actually works.

Let's say, I am currently working on an application that creates a package format similar to the ZIP format. For ease of access, I want to create a shell extension that works similar to how Pismo File Mount works. For those who have not used Pismo File Mount before, this is how it works:

1. The user right-clicks a ZIP file in Windows Explorer.
2. The user then clicks "Mount" to mount the ZIP file.
3. The user can now access his/her files immediately.
4. The user does not have to extract the ZIP file to view its contents.

There's a catch. I do not want to use the Pismo File Mount API, perhaps for various reasons like commercial or legal ones.

The question is, how does Pismo File Mount integrate itself into Windows Explorer programmatically, in terms of the Windows API and C++?

Answer 1

There exist two ways:

1. Shell namespace extension. The folder created by the shell namespace extension is not an actual filesystem folder and accessibility of the files in such folder is usually limited to Explorer itself and applications aware of shell extensions and the ways to work with them.

2. Filesystem filter driver which creates a virtual directory on the existing disk. Such directory is seen by all applications as a real directory, where those applications can read and write files and subdirectories. All filesystem operations go through such driver.

Pismo File Mount works via the filter driver, AFAIK.

Our CallbackFilter product provides a way to create virtual directories and files. It includes a driver and calls your user-mode code for actual operations. But filter approach is a bit complicated -- a virtual disk created with a filesystem driver (eg. with our Callback File System product) is easier to implement and manage due to differences in architectures of the filter driver stack and filesystem drivers.