linux-kernel - Re: [PATCH 1/5] tools: Add err.h with ERR_PTR PTR

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Date:	Tue, 8 Sep 2015 18:06:52 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Raphaël Beamonte <raphael.beamonte@...il.com>
Cc:	Jiri Olsa <jolsa@...nel.org>, lkml <linux-kernel@...r.kernel.org>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH 1/5] tools: Add err.h with ERR_PTR PTR_ERR interface

Em Tue, Sep 08, 2015 at 04:22:39PM -0400, Raphaël Beamonte escreveu:
> 2015-09-07 4:38 GMT-04:00 Jiri Olsa <jolsa@...nel.org>:
> > Adding part of the kernel's <linux/err.h> interface:
> >   inline void * __must_check ERR_PTR(long error);
> >   inline long   __must_check PTR_ERR(__force const void *ptr);
> >   inline bool   __must_check IS_ERR(__force const void *ptr);
> >
> > it will be used to propagate error through pointers
> > in following patches.
> >
> > Link: http://lkml.kernel.org/n/tip-ufgnyf683uab69anmmrabgdf@git.kernel.org
> > Signed-off-by: Jiri Olsa <jolsa@...nel.org>
> > ---
> >  tools/include/linux/err.h | 49 +++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> >  create mode 100644 tools/include/linux/err.h
> >
> > diff --git a/tools/include/linux/err.h b/tools/include/linux/err.h
> > new file mode 100644
> > index 000000000000..c9ada48f5156
> > --- /dev/null
> > +++ b/tools/include/linux/err.h
> > @@ -0,0 +1,49 @@
> > +#ifndef __TOOLS_LINUX_ERR_H
> > +#define __TOOLS_LINUX_ERR_H
> > +
> > +#include <linux/compiler.h>
> > +#include <linux/types.h>
> > +
> > +#include <asm/errno.h>
> > +
> > +/*
> > + * Original kernel header comment:
> > + *
> > + * Kernel pointers have redundant information, so we can use a
> > + * scheme where we can return either an error code or a normal
> > + * pointer with the same return value.
> > + *
> > + * This should be a per-architecture thing, to allow different
> > + * error and pointer decisions.
> > + *
> > + * Userspace note:
> > + * The same principle works for userspace, because 'error' pointers
> > + * fall down to the unused hole far from user space, as described
> > + * in Documentation/x86/x86_64/mm.txt for x86_64 arch:
> > + *
> > + * 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm hole caused by [48:63] sign extension
> > + * ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
> > + *
> > + * It should be the same case for other architectures, because
> > + * this code is used in generic kernel code.
> > + */
> > +#define MAX_ERRNO      4095
> > +
> > +#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)
> > +
> > +static inline void * __must_check ERR_PTR(long error)
> > +{
> > +       return (void *) error;
> > +}
> > +
> > +static inline long __must_check PTR_ERR(__force const void *ptr)
> > +{
> > +       return (long) ptr;
> > +}
> > +
> > +static inline bool __must_check IS_ERR(__force const void *ptr)
> > +{
> > +       return IS_ERR_VALUE((unsigned long)ptr);
> > +}
> > +
> > +#endif /* _LINUX_ERR_H */
> > --
> > 2.4.3
> 
> Perhaps a dumb question, but it seems the code is exactly the same as
> in linux/err.h besides the part of the comment you added. Why not
> using that file directly in the other patches then?

We can't do that.

Read:

commit 3f735377bfd6567d80815a6242c147211963680a
Author: Arnaldo Carvalho de Melo <acme@...hat.com>
Date:   Sun Jul 5 22:48:21 2015 -0300

    tools: Copy lib/rbtree.c to tools/lib/
    
    So that we can remove kernel specific stuff we've been stubbing out via
    a tools/include/linux/export.h that gets removed in this patch and to
    avoid breakages in the future like the one fixed recently where
    rcupdate.h started being used in rbtree.h.


--------------------------

There are more copies like that, but the explanation above should be
enough, no?


- Arnaldo
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