Question

I have been looking into libraries for a file system that will allow path mounting on purely an application level. This may not be called just “path mounting” since that has the connotation of os level path mounting, but something else, I am not sure of the terminology. I was hoping to be able to find a few but were unable to find anything to what I am looking for (boost::filesystem was the closest I found). I wanted to be able to compare several different libraries in hopes of seeing what advantages and disadvantages they have.

What I mean by a file system with path mounting is so I would have a path such as

"SomeRoot:data\file.txt"

and the "SomeRoot" would be replaced with C:\SomeFolder", which would be set to the file mount system.

Does anyone know of a file system that will allow path mounting?

Edit:

Since it appears that there may not be many libraries for this, I would also be interested in how to construct one properly.

Answer 1

If you are looking for an “application level file system” then at the most basic level, you are going to need to do a string replace. On the most basic level there are two strings

MountPoint
Which will be used as the “mount point”, such as your SomeRoot.

MountResolve
Which is the location to what mount point is pointed at for when “resolving” a file location. This is the same as your C:\SomeFolder.

Besides for the obvious accessor and getters for those variables, there is the need for a function to resolve the path, which is this case can be

bool ResolvePath(const String& mountPath, String& resolvedPath);

The contents of the ResolvePath are very simple, all you need to do is replace the current MountPoint string in mountPath and place the result into resolvedPath.

resolvedPath = mountPath;
resolvedPath.replace(0, mMountPoint.size() + 1, mMountResolve.c_str(), mMountResolve.size());

However, there is more that can be done in that function. The reason why I have it returning a bool is because the function should fail mountPath does not have the MountPoint. To check, just do a simple string::find.

if(mountPath.find(mMountPoint) == String::npos)
    return false;

With this, you can now resolve SomeRoot:data\file.txt to C:\SomeFolder\data\file.txt if MountResolve is set to C:\SomeFolder\. However, you mentioned without the trailing slash at the end. Since there is nothing to be currently done to verify that slash, your result would be C:\SomeFolderdata\file.txt. This is wrong.

On your access for setting the mount resolve, you want to check to see if there is there is a trailing folder slash. If there is not, then add it.

void FileSystem::SetMountResolve(const String& mountResolve)
{
    mMountResolve = mountResolve;

    if(*(mMountResolve.end() - 1) != FOLDERSLASH)
        mMountResolve += FOLDERSLASH;
}

This will allow a basic “FileSystem” class to have one MountPoint/MountResolve. It will not be very difficult to extend this to allow multiple mount points either.