linux-kernel - Re: [PATCH 09/13] Move bp_type_idx to kernel/event/hw

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Date:	Tue, 15 Sep 2015 21:39:10 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Palmer Dabbelt <palmer@...belt.com>
Cc:	arnd@...db.de, dhowells@...hat.com, viro@...iv.linux.org.uk,
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	fweisbec@...il.com
Subject: Re: [PATCH 09/13] Move bp_type_idx to kernel/event/hw_breakpoint.c

On Tue, Sep 15, 2015 at 11:40:11AM -0700, Palmer Dabbelt wrote:
> On Tue, 15 Sep 2015 01:06:07 PDT (-0700), peterz@...radead.org wrote:
> > On Mon, Sep 14, 2015 at 03:50:43PM -0700, Palmer Dabbelt wrote:
> >> This has a "#ifdef CONFIG_*" that used to be exposed to userspace.
> >>
> >> The names in here are so generic that I don't think it's a good idea
> >> to expose them to userspace (or even the rest of the kernel).  Since
> >> there's only one kernel user, it's been moved to that file.
> >>
> >> Signed-off-by: Palmer Dabbelt <palmer@...belt.com>
> >> Reviewed-by: Andrew Waterman <waterman@...s.berkeley.edu>
> >> Reviewed-by: Albert Ou <aou@...s.berkeley.edu>
> >> ---
> >>  include/uapi/linux/hw_breakpoint.h | 10 ----------
> >>  kernel/events/hw_breakpoint.c      | 10 ++++++++++
> >>  2 files changed, 10 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/include/uapi/linux/hw_breakpoint.h b/include/uapi/linux/hw_breakpoint.h
> >> index b04000a2296a..7a6a5a7f9511 100644
> >> --- a/include/uapi/linux/hw_breakpoint.h
> >> +++ b/include/uapi/linux/hw_breakpoint.h
> >> @@ -17,14 +17,4 @@ enum {
> >>  	HW_BREAKPOINT_INVALID   = HW_BREAKPOINT_RW | HW_BREAKPOINT_X,
> >>  };
> >>
> >> -enum bp_type_idx {
> >> -	TYPE_INST 	= 0,
> >> -#ifdef CONFIG_HAVE_MIXED_BREAKPOINTS_REGS
> >> -	TYPE_DATA	= 0,
> >> -#else
> >> -	TYPE_DATA	= 1,
> >> -#endif
> >> -	TYPE_MAX
> >> -};
> >
> > This is rather unfortunate; you are correct that the naming is too
> > generic (and I tend to agree), but I think these values are required by
> > userspace to fill out:
> >
> >   perf_event_attr::bp_type
> >
> > So removing them will break things.
> >
> > Frederic?
> 
> perf_event_open(2) says
> 
>        bp_type (since Linux 2.6.33)
>               This chooses the breakpoint type.  It is one of:
> 
>               HW_BREAKPOINT_EMPTY
>                      No breakpoint.
> 
>               HW_BREAKPOINT_R
>                      Count when we read the memory location.
> 
>               HW_BREAKPOINT_W
>                      Count when we write the memory location.
> 
>               HW_BREAKPOINT_RW
>                      Count when we read or write the memory location.
> 
>               HW_BREAKPOINT_X
>                      Count when we execute code at the memory location.
> 
>               The values can be combined via a bitwise or, but the combination
>               of HW_BREAKPOINT_R or HW_BREAKPOINT_W  with  HW_BREAKPOINT_X  is
>               not allowed.
> 
> so I think removing this enum from userspace is OK.  Did I miss
> something?

Nah, could've just been me not being awake. Unless Frederic says
otherwise I'll chalk it up to not having drank enough morning juice.
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