Subject: Re: bug#65486: [PATCH] syscalls: Add support for musl libc

From: Sören Tempel <[email-masked]>
Date: Wed, 13 Sep 2023 12:23:50 +0200

Hi Ludovic,

Ludovic Courtès <[email-masked]> wrote:
> I think this is misleading because this has to do with the C library,
> not with the kernel (“linux variant”).
> 
> For example, GNU/Hurd uses the same C library as GNU/Linux, and both
> should use “statfs64”, “readdir64”, etc.

Oh, right! I totally forgot about GNU/Hurd, thanks for pointing that out.

> So what we want to check is whether we’re using the GNU libc or Musl,
> regardless of the kernel.

Keep in mind that—contrary to glibc—musl only supports Linux and not
GNU/Hurd. Therefore, it should be sufficient to simply check for a
linux-musl host and then use statfs/readdir over statfs64/readdir64:

	(let ((proc (syscall->procedure (if linux-musl?
	                                      "readdir"
	                                      "readdir64"))))
	  ........

Would that be acceptable?

> Now, instead of checking the libc’s identity, we could check whether
> “statfs64” is available, and if not, fall back to “statfs”.

You mean using a GNU ./configure check? That would be possible. However,
I think we also need to check somehow that readdir/statfs return values
are struct-layout compatible with the readdir64/statfs64 versions used
by glibc.

Unfortunately, I am not deeply familiar with GNU autotools. Is there a
similar feature-check in the Guile code base already that I could use as
a source of inspiration? Maybe the if expression outlined above would
be sufficient for now and we can improve upon that later?

Greetings,
Sören