Re: git: b165e9e3ea4e - main - Add fchroot(2)

On 1129T1724, Konstantin Belousov wrote:
> On Fri, Nov 29, 2024 at 12:22:16PM +0000, Edward Tomasz Napierala wrote:
> > The branch main has been updated by trasz:
> > 
> > URL: https://cgit.FreeBSD.org/src/commit/?id=b165e9e3ea4e327fc421d81c2a89242bd8720780
> > 
> > commit b165e9e3ea4e327fc421d81c2a89242bd8720780
> > Author:     Edward Tomasz Napierala <trasz@FreeBSD.org>
> > AuthorDate: 2024-11-29 07:46:07 +0000
> > Commit:     Edward Tomasz Napierala <trasz@FreeBSD.org>
> > CommitDate: 2024-11-29 12:10:02 +0000
> > 
> >     Add fchroot(2)
> >     
> >     This is similar to chroot(2), but takes a file descriptor instead
> >     of path.  Same syscall exists in NetBSD and Solaris.  It is part of a larger
> >     patch to make absolute pathnames usable in Capsicum mode, but should
> >     be useful in other contexts too.
> 
> I wonder if it should be fchrootat(fd, path, flags) with the support for
> AT_EMPTY_PATH instead.  Then fchroot() becomes the libc wrapper.
> 
> I can see arguments both pro and contra.  Main argument against is that
> the immediate semantic is easily emulated by openat() + fchroot().  But
> the freedom of adding the fchroot-specific flags might be worth considering.

Yeah, I thought about that too.  In the end I decided to go with the simpler
API, because I like how it mirrors fchdir(2); both do something fundamentally
very similar, they set the default starting points for path lookups.
And we never had the need to add fchdirat(2).