Please add an API for readonly files

[xnorai]

Currently gguf-tools (as used in e.g. MLX - a popular choice on Apple platforms) cannot open *.gguf files on iOS, if those gguf files are in the app bundle. The root cause is it always seems to open files in read/write mode, and then it also mmaps writable regions, both of which fail on iOS because bundled data is very much read-only by design. I imagine there could be other circumstances where read-only access is desirable.

It'd be great if there was a readonly mode for read-only access.

[xnorai]

Here's what I mean. This, obviously, is not a complete fix because it permanently switches things into read-only mode, which is not suitable for all circumstances. That is how we patched it for our own specific needs.

0001-Open-files-in-readonly-mode.patch