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Date: Mon, 12 Jun 2017 14:07:40 -0400
From: Rich Felker <>
Subject: Re: ENOSYS/EOPNOTSUPP fallback?

On Mon, Jun 12, 2017 at 07:55:20PM +0200, Joakim Sindholt wrote:
> On Sun, Jun 11, 2017 at 02:57:59PM -0600, Benjamin Slade wrote:
> > Thank you for the extensive reply.
> > 
> > Just to be clear: I'm just an end-user of flatpak, &c. As far as I can
> > tell, flatpak is making use of `ostree` which assumes that the libc will
> > take care of handling `dd` fallback (I got the impression that flatpak
> > isn't directly calling `fallocate` itself).
> I don't think it's fair to say that they depend on the fallback. POSIX
> is very clear that posix_fallocate doesn't fail in the way musl fails
> here[1]. They (hopefully) expect it to behave as described in the
> standard and there's not much musl can do to alleviate the problem.

I don't follow what you mean by "POSIX is very clear...". Any
interface that has defined errors is permitted by POSIX to fail for
other implementation-defined reasons as long as the error codes used
for those reasons don't clash with the standard errors. In any case
there is no way musl can implement posix_fallocate if the underlying
kernel/filesystem does not support it.

I followed up on the flatpak bug tracker thread with some additional
info. But I'm not clear what functionality they actually need from
posix_fallocate because I don't even know what they're doing with it.


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