KACL from KIO isn't really POSIX-compliant

[Adriaan de Groot]

On 2020 dekula d. 11id 16:37:19 CET Aleix Pol wrote:
> > I tried compiling kio/src/core/kacl.cpp on FreeBSD, which does support
> > POSIX ACLs, and failed. This is because KACL's code uses non-standard
> > Linux-specific acl_* functions. I tried implementing them using standard
> > ones and it turned out to be impossible, mainly because types like acl_t
> > are opaque to the user of the library.

[[ I'm aware of Gleb's work, I'd really like a non-FreeBSD perspective on this 
]]

Here's *part* of the problem:

bool KACL::operator==(const KACL &rhs) const
{
#if HAVE_POSIX_ACL
    return (acl_cmp(d->m_acl, rhs.d->m_acl) == 0);
#else
    Q_UNUSED(rhs);
    return true;
#endif
}

It *looks* like portable code, it's checking if POSIX is available, does a 
comparison, that's fine. Except that acl_cmp() is **not** a POSIX function.

https://man7.org/linux/man-pages/man3/acl_cmp.3.html

The POSIX ACL spec sucks. There is no way to compare sets of ACLs. So the non-
portable Linux-specific function makes a lot of sense: that **should** have 
been in POSIX.

Gleb's question is about where this should be fixed. FreeBSD's libc is the 
"obvious" solution, because this is generally useful ACL API, but fixing up 
libc, especially with something grotty like a Linux-specific function 
(opinions expressed may not be my own) is a slooooowww process. But doing the 
same thing in KIO itself means a huge code bloat in KIO.

[ade]
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