Re: [PATC 7/9] Skipping drm build, unsupported

[Eric Blake]

On 6/30/20 11:53 AM, Gerd Hoffmann wrote:
> > > > > -util-obj-$(CONFIG_POSIX) += drm.o
> > > > > +util-obj-$(CONFIG_LINUX) += drm.o
> > >
> > > Can't see anything linux-specific there.  Also note that FreeBSD (and
> > > possibly other *BSDs too) have drm support.  So CONFIG_POSIX looks
> > > correct to me.
> >
> > This change was my suggestion; I assumed that "open /dev/dri/whatever"
> > was Linux-specific. The specific thing that doesn't work on
> > Haiku, or on Solaris for that matter, is that the code uses
> > DT_CHR, which isn't in POSIX but is a Linux-and-BSDism.
>
> Ah, that is the problem.  Yes, DT_CHR is an non-posix optimization which
> allows to get the file type directly, without another round-trip to the
> kernel.  If that isn't available you can stat() the file and check
> ((st_mode & S_IFMT) == S_IFCHR) instead.

Even when d_type and DT_CHR is available, there are filesystems where 
the Linux kernel reports d_type of DT_UNKNOWN, and where you are best 
having that code also falling back to an fstat().  In short, any 
portable code that uses d_type should have fallback code for DT_UNKNOWN, 
at which point porting to systems without d_type is as easy as writing 
an accessor macro that returns d_type when it exists and DT_UNKNOWN 
where it doesn't.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
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