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Date: Fri, 15 Jan 2016 17:20:27 +0100
From: Felix Janda <felix.janda@...teo.de>
To: musl@...ts.openwall.com
Subject: Re: [PATCH] add _DIRENT_HAVE_D_* constants to dirent.h
Rich Felker wrote:
> On Thu, Jan 14, 2016 at 05:44:49PM -0500, Rich Felker wrote:
> > On Wed, Jan 13, 2016 at 07:09:19PM +0100, Felix Janda wrote:
> > > they can be used for checking existence of non-standard fields of
> > > struct dirent, are used by various programs to avoid configure
> > > checks and are at least present on glibc, uclibc, dietlibc and
> > > newlib.
> > > ---
> > > The motivation for this patch is
> > >
> > > http://oss.sgi.com/archives/xfs/2016-01/msg00388.html
> > > ---
> > > include/dirent.h | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/include/dirent.h b/include/dirent.h
> > > index 5aa8510..b2ffe8a 100644
> > > --- a/include/dirent.h
> > > +++ b/include/dirent.h
> > > @@ -57,6 +57,9 @@ int getdents(int, struct dirent *, size_t);
> > > #endif
> > >
> > > #ifdef _GNU_SOURCE
> > > +#define _DIRENT_HAVE_D_OFF
> > > +#define _DIRENT_HAVE_D_RECLEN
> > > +#define _DIRENT_HAVE_D_TYPE
> > > int versionsort(const struct dirent **, const struct dirent **);
> > > #endif
> >
> > I like the concept of defining macros to publish the availability of
> > extensions like this, but I don't think they should be dependent on
> > _GNU_SOURCE. At the very least they should also be available under
> > _DEFAULT_SOURCE (_BSD_SOURCE), but since they're in the reserved
> > namespace (underscore followed by capital) I'd prefer to have them
> > exposed unconditionally.
I see.
> > I'm also skeptical of whether d_off and d_reclen should be promoted as
> > public APIs. They don't seem to be useful (unlike d_type which is
> > highly useful) and may lock down some assumptions about
> > implementation.
>
> Perhaps to make a discussion of this more concrete: is there other
> software that's using the d_reclen or d_off fields conditionally on
> having the above macros defined? What is is using them for?
I had not checked specifically how much each macro is used. (I'm using
debian codesearch.) _DIRENT_HAVE_D_TYPE seems to be used the most
often. The only other (apart from xfsprogs) use of the others is in
glusterfs:
http://sources.debian.net/src/glusterfs/3.7.6-1/api/src/glfs-fops.c
It seems to be used in the glfs_readdir* functions to convert the
internal gf_dirent structure to the usual dirent. Likely few people
rely on the d_reclen or d_off from a dirent received via
glfs_readdir*...
> I read the above-linked mailing list discussion and I think the
> autoconf test is a better approach than depending on the macros (since
> they're not present on older musl or on other non-glibc libcs/systems)
They seem to be present on most libcs on linux.
> but we should probably add at least _DIRENT_HAVE_D_TYPE and perhaps
> the others too.
Thanks,
Felix
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