Sparse files

[essen]

Hello! I am looking into implementing more functionality out of fallocate, starting with the ability to punch holes (FALLOC_FL_PUNCH_HOLE) to deallocate space in the middle of files.

This is possible on Linux via fallocate, macOS via fcntl and Windows (NTFS) via DeviceIoControl. Not sure about others but I think it's a good enough start.

I could see inserting holes in files (FALLOC_FL_INSERT_RANGE) or collapsing files (FALLOC_FL_COLLAPSE_RANGE) as being potentially useful for RabbitMQ.

I am looking for pointers on what the interface should look like, as much of the work to implement this deals with file, prim_file and raw_file_* modules. Should I add a file:allocate/4 with an option list, or make a new function dedicated to creating/collapsing holes?

[jhogberg]

Thanks for raising this issue!

This is rather platform-specific, and the file module's convention of trying to be maximally compatible makes it difficult to support this in a nice way. I'm hoping to get around to refactoring file access in general some time in the future, with platform-specific things in platform-specific modules rather than trying to shoehorn it all into the same kind-of-sort-of portable module. I don't think we'd like to add this before then however.

[essen]

Fair enough. I'll put this back to the bottom of the list for now then.