linux-kernel - Re: [patch 02/21] perfmon2 minimal: generic headers

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Message-ID: <7c86c4470806110049g76247b4ex5e1b77af78d8dd7c@mail.gmail.com>
Date:	Wed, 11 Jun 2008 09:49:44 +0200
From:	"stephane eranian" <eranian@...glemail.com>
To:	"Arjan van de Ven" <arjan@...radead.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [patch 02/21] perfmon2 minimal: generic headers

Arjan,


On Tue, Jun 10, 2008 at 4:29 PM, Arjan van de Ven <arjan@...radead.org> wrote:
> On Mon, 09 Jun 2008 15:33:40 -0700 (PDT)
> eranian@...glemail.com wrote:
>
>> +#ifndef __LINUX_PERFMON_H__
>> +#define __LINUX_PERFMON_H__
>> +
>> +/*
>> + * This file contains all the user visible generic definitions for
>> the
>> + * interface. Model-specific user-visible definitions are located in
>> + * the asm/perfmon.h file.
>> + */
>> + */
>> +#define PFM_BVSIZE(x)        (((x)+(sizeof(u64)<<3)-1) /
>> (sizeof(u64)<<3)) +#define PFM_PMD_BV PFM_BVSIZE(PFM_MAX_PMDS)
>
> can't use u64 in userspace headers; must use __u64
>
>
Will fix that.


>> + * default value for the user and group security parameters in
>> + * /proc/sys/kernel/perfmon/sys_group
>> + * /proc/sys/kernel/perfmon/task_group
>
> hmmm that smells funky.
>
Will clarify this.


>> +/*
>> + * perfmon version number
>> + */
>> +#define PFM_VERSION_MAJ               2U
>> +#define PFM_VERSION_MIN               99U
>> +#define PFM_VERSION           (((PFM_VERSION_MAJ&0xffff)<<16)|\
>> +                               (PFM_VERSION_MIN & 0xffff))
>> +#define PFM_VERSION_MAJOR(x)  (((x)>>16) & 0xffff)
>> +#define PFM_VERSION_MINOR(x)  ((x) & 0xffff)
>
> I'm very nervous when seeing something like this in userspace headers;
> you need to assume that the app has been compiled with a very different
> version of the headers than the currently running kernel.... either the
> version of perfmon doesn't matter, in which case these don't belong
> here, or it does and it should be a runtime query.
>
I think you bring up a good point. There is indeed a way of querying the version
via /sysfs.

However the question is how does an application know which API version
it was compiled
for, so it can compare with what it finds in /sysfs? That ought to be
somewhere in the
public headers that the application was compiled with.


>
>
>> +#ifndef __LINUX_PERFMON_KERN_H__
>> +#define __LINUX_PERFMON_KERN_H__
>> +/*
>> + * This file contains all the definitions of data structures,
>> variables, macros
>> + * that are to be shared between generic code and arch-specific code
>> + *
>> + * For generic only definitions, use perfmon/perfmon_priv.h
>> + */
>> +#ifdef __KERNEL__
>
> no need for #ifdef __KERNEL__, just don't expose the header to
> userspace.
>
You are right. Will remove that.

>> +/*
>> + * logging
>> + */
>> +#define PFM_ERR(f, x...)  printk(KERN_ERR     "perfmon: " f "\n", ##
>> x) +#define PFM_WARN(f, x...) printk(KERN_WARNING "perfmon: " f "\n",
>> ## x) +#define PFM_LOG(f, x...)  printk(KERN_NOTICE  "perfmon: " f
>> "\n", ## x) +#define PFM_INFO(f, x...) printk(KERN_INFO    "perfmon:
>> " f "\n", ## x) +
>
> hmmm what's wrong with the current set of macros the kernel has for
> these?
>
I think these simply prefix the message with "perfmon:" so you know
which subsystems the messages are from.
You do it in one place instead of duplicating the "perfmon: " string everywhere.
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