从异构 Linux 系统中的共享 Memory 创建虚拟 FS

Question

I'm developing a measurement device, with 2 CPUs and a shared memory:

=>[ CPU:0 RTOS/Measurements ]         [ CPU: 1 Linux/User]
                 \                   /          |   
                  \[ Shared Memory ]/           |
                     struct HotData              /measure
                       { int x;          ->              /x
                         char[20] y;     ->              /y
                         long z; };      ->              /z

Currently, I have a shared memory, where CPU-0 measures some data and cyclically updates the structure "HotData". I do not want to touch the code on CPU-0 for real-time limitations. On the other hand, the Linux kernel can access this shared space and read the latest data.

Next, I want to create a "super lightweight" virtual filesystem on Linux to map those data fields, each to a file. So any user app/script can easily access "/measure/x" for example and get the latest measurement.

1. What's the fastest (lightweight) way to map the data from the shared physical address into a user-space file?
2. For sure I have to implement the open/read functions for the VFS, is there a quick example/project to follow?

Answer 1

You may wish to look at FUSE (Filesystem in User Space). It's a filesystem driver (shipped by default with many Linux distributions) that allows you to mount a virtual filesystem provided by normal unprivileged application/process.
(Think NFS, but local - and it's not restricted to the NFS protocol. There are existing FUSE solutions for mounting an remote SFTP servers, and even one presenting Wikipedia as a file/directory structure, if I recall...)

There's bindings and libraries for loads of languages - there's an example in Python which shows just how easy it is to implement a virtual filesystem with it.

Sounds like you might be working in C/C++, in which case you probably want libfuse (official example code linked). There's what appears to be a straightforward C tutorial over on Medium .