Writable CD Filesystems

[otac0n]

I'm opening this tracking issue for writable CD filesystems.

https://github.com/LTRData/DiscUtils/blob/LTRData.DiscUtils-initial/Library/DiscUtils.Iso9660/VfsCDReader.cs#L34

Currently VfsCDReader inherits VfsReadOnlyFileSystem. I need (and will consider implementing) read/write support.

[Olof-Lagerkvist]

ISO images are normally modified by building a new ISO image and adding what you need from the previous one and then adding updated files etc. That is, creating a CDReader for the old image and a CDBuilder and then copy files from the reader to the builder. It is often easy and reasonably efficient to do this with DiscUtils, because files added from existing image do not need to be buffered, they could be added as streams. Later when you call Build on the CDBuilder, data is compiled by actually reading from the original image and your new files.

[otac0n]

Yes, I have a project where everything is buffered as streams, even chunked files:

        // Demux
        var baseStream = parent.File.Open(parentRelativePath, parentOptions);
        Stream stream = new ConcatStream(
            Ownership.Dispose,
            [.. entry.Chunks.Select(c => new OffsetStreamSpan(baseStream, c.Position, c.Size, Ownership.Dispose))]);

(sorry hit submit on accident)

So the goal is to support in-place editing of files. Reencoding an entire file for random access writes is tough. I could do this recursively on Close() but flush to memory otherwise. The problem is that I do want shared file access if & whenever possible.