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

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Message-ID: <55f8660b.84bd440a.620d1.ffffe1cb@mx.google.com>
Date:	Tue, 15 Sep 2015 11:40:11 -0700 (PDT)
From:	Palmer Dabbelt <palmer@...belt.com>
To:	peterz@...radead.org
CC:	fweisbec@...il.com
Subject:     Re: [PATCH 09/13] Move bp_type_idx to kernel/event/hw_breakpoint.c

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?
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