Re: Need help understanding how scm_init_guile works (with FUSE)

Hi Daniel!
Just simply took a glance at the code, I'm curious why you don't just call
scm_init_guile() in fuse operation init function?
This should let you call scm_init_guile() just once.

Best regards.


On Mon, Mar 3, 2025 at 6:41 PM Daniel Littlewood via General Guile related
discussions <[email protected]> wrote:

> Hi guile-users,
>
> I am working on a guile program to interact with FUSE. The code is at
> https://gitlab.com/danielittlewood0/diffuse. I have managed to get it to
> basically work, but there are some things I don't understand. It
> consists of essentially two files at the moment:
>
>   * other.scm, which implements the actual logic of the filesystem in
> guile.
>   * hello.c, which does the plumbing into the FUSE library.
>
> I managed to get it to work by doing the following in each of the FUSE
> handlers:
>
> scm_init_guile()
> scm_c_primitive_load("/full/path/to/other.scm")
> scm_call_1(scm_variable_ref(scm_c_lookup("whatever-function-I-want")))
>
> That worked fine, but I was a bit confused about having to call
> scm_init_guile so many times. I expected to just call it once in main
> and then never again. If I do that, i.e. just move scm_init_guile to
> main and remove all the other callers (rest of the code unchanged) I get
> a segfault.
>
> I was also surprised that I had to give the absolute file path of my
> guile script to scm_c_primitive_load. If I called it from main then I
> didn't have to do that. If I call scm_c_primitive_load from main then I
> can give a relative path, but from e.g. hello_read I get a "No such file
> or directory" error and have to provide the absolute path.
>
> I think this is something peculiar to how FUSE is set up, but I don't
> know what exactly. I don't actually call the handlers, I pass the
> function pointers to the library and the library calls them for me. For
> instance if I try to print the current working directory from within one
> of the handlers, I get / - which probably refers to the root of the FUSE
> filesystem tree. I managed to avoid giving the absolute path by calling
> scm_init_guile() and then scm_c_primitive_load("other.scm") from main.
> This works (with the relative path). What's surprising to me is:
>
>   * I still have to call scm_init_guile before every use of guile within
>     the current function, even if I called it in main.
>   * When I call scm_init_guile a second time, I don't have to call
>     scm_primitive_load a second time. I can just call scm_variable_ref
>     immediately.
>
> This is a bit confusing to me. I could understand if I had to load the
> code every time I call scm_init_guile (although then I'd want to reduce
> the boilerplate) and I could understand calling scm_init_guile and
> scm_c_primitive_load only once, but the arrangement above doesn't make
> sense to me. I feel like I must be missing something.
>
> Note that this is the first project I've really written in either C or
> guile, so I might be missing something obvious.
>
> Best wishes,
> Dan
>