Date:	Thu, 26 Jul 2012 15:50:11 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	lenb@...nel.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, joe@...ches.com,
	isimatu.yasuaki@...fujitsu.com, liuj97@...il.com,
	srivatsa.bhat@...ux.vnet.ibm.com, prarit@...hat.com,
	imammedo@...hat.com, vijaymohan.pandarathil@...com
Subject: Re: [PATCH v3 1/4] ACPI: Add acpi_pr_<level>() interfaces

On Thu, 2012-07-26 at 15:37 -0600, Bjorn Helgaas wrote:
> On Thu, Jul 26, 2012 at 02:58:50PM -0600, Toshi Kani wrote:
> > On Thu, 2012-07-26 at 13:22 -0600, Bjorn Helgaas wrote:
> > > On Wed, Jul 25, 2012 at 5:12 PM, Toshi Kani <toshi.kani@...com> wrote:
> > > > This patch introduces acpi_pr_<level>(), where <level> is a kernel
> > > > message level such as err/warn/info, to support improved logging
> > > > messages for ACPI, esp. in hotplug operations.  acpi_pr_<level>()
> > > > appends "ACPI" prefix and ACPI object path to the messages.  This
> > > > improves diagnostics in hotplug operations since it identifies an
> > > > object that caused an issue in a log file.
> > > >
> > > > acpi_pr_<level>() takes acpi_handle as an argument, which is passed
> > > > to ACPI hotplug notify handlers from the ACPICA.  Therefore, it is
> > > > always available unlike other kernel objects, such as device.
> > > >
> > > > For example, the statement below
> > > >   acpi_pr_err(handle, "Device don't exist, dropping EJECT\n");
> > > > logs an error message like this at KERN_ERR.
> > > >   ACPI: \_SB_.SCK4.CPU4: Device don't exist, dropping EJECT
> > > >
> > > > ACPI drivers can use acpi_pr_<level>() when they need to identify
> > > > a target ACPI object in their messages, such as error messages.
> > > 
> > > It's definitely an improvement to have *something* that identifies a
> > > device in these messages.  But the ACPI namespace path is not really
> > > intended to be user-consumable, so I don't think we should expose it
> > > indiscriminately.  I think we should be using the ACPI device name
> > > ("PNP0C02:00") whenever possible.  Given the device name, we can get
> > > the path from the sysfs "path" file.
> > 
> > Hi Bjorn,
> > 
> > Thanks for reviewing!  Yes, ACPI device path is not good for regular
> > users to analyze from the info.  I also agree with you that device name
> > is a better choice when users always diagnose issues by themselves right
> > after they performed an operation.  However, there are also cases that
> > users ask someone to diagnose an issue remotely from the log files, and
> > hotplug operations are performed automatically.  In such cases, using
> > ACPI device name alone is problematic for hotplug operations since a
> > device name comes with an instance number that continues to change with
> > hot-add/remove operations.  Here is one example scenario.  Let's say,
> > user has automatic load-balancer or power-saving that can trigger
> > hundreds of CPU hotplug operations per a day.  This user then found that
> > there were multiple hotplug errors logged in the past few days, and
> > asked an IT guy to look at the error messages.  When this user found the
> > issue, all device names are gone from sysfs after repeated hotplug
> > operations.  This IT guy would have no idea if those errors were
> > happening on a particular device or not from the error messages since
> > their instance numbers continue to change.
> 
> I agree that it's useful to be able to debug from the dmesg log
> without having to ask a user to collect stuff from /sys.  But rather
> than including the namespace path in every message, I think it'd be
> better to do one dev_info() in the hotplug notify event handler and
> include the path there.  Subsequent messages can just use dev_info()
> without the namespace info.

Hi Bjorn,

I agree.  For now, I will keep the use of acpi_pr_<level>() within the
hotplug notify handler functions.  I will change any subsequent
functions to use dev_<level>().  This way, we have only one use of
acpi_pr_<level>() in an operation.  I will also clarify this in the
change log.

> > > Another possible approach to this is to add a %p extension rather than
> > > adding acpi_printk().  Then you could do, e.g., 'printk("%pA ...\n",
> > > handle)', and printk could interpolate the namespace path.  But I
> > > really think there should be very few places where we need the path,
> > > so I'm not sure it's worth it.
> > 
> > Address of handle is not very helpful either when someone needs to
> > analyze from log files.
> 
> Sorry, I should have made this clearer.  The %pA would expand to the ACPI
> namespace path, so a "dev_info(dev, "new device for %pA\n", dev->handle)"
> would produce output like this:
> 
>     PNP0C01:00: new device for \_SB_.PCI0.ISA_.MBIO
> 
> I fiddled with this a while ago; it would look something like this:

I see.  That sounds good idea.  I agree that we can use it when device
is valid.  Since it's late to make such changes, I will consider making
such changes for 3.7. 

Thanks,
-Toshi


> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index c3f36d41..201dcdb 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -551,6 +551,29 @@ char *symbol_string(char *buf, char *end, void *ptr,
>  #endif
>  }
>  
> +#ifdef CONFIG_ACPI
> +#include <acpi/acpi.h>
> +
> +static noinline_for_stack
> +char *acpi_name_string(char *buf, char *end, acpi_handle handle,
> +		       struct printf_spec spec, const char *fmt)
> +{
> +	acpi_status status;
> +	struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> +	u32 type = ACPI_SINGLE_NAME;
> +	char *p = buf;
> +
> +	if (fmt[0] == 'A')
> +		type = ACPI_FULL_PATHNAME;
> +
> +	status = acpi_get_name(handle, type, &buffer);
> +	if (ACPI_SUCCESS(status))
> +		p = string(buf, end, buffer.pointer, spec);
> +	kfree(buffer.pointer);
> +	return p;
> +}
> +#endif
> +
>  static noinline_for_stack
>  char *resource_string(char *buf, char *end, struct resource *res,
>  		      struct printf_spec spec, const char *fmt)
> @@ -921,6 +944,8 @@ int kptr_restrict __read_mostly;
>   *
>   * Right now we handle:
>   *
> + * - 'A' For full ACPI namespace names
> + * - 'a' For single segment ACPI namespace names
>   * - 'F' For symbolic function descriptor pointers with offset
>   * - 'f' For simple symbolic function names without offset
>   * - 'S' For symbolic direct pointers with offset
> @@ -982,6 +1007,9 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  	}
>  
>  	switch (*fmt) {
> +	case 'A':
> +	case 'a':
> +		return acpi_name_string(buf, end, ptr, spec, fmt);
>  	case 'F':
>  	case 'f':
>  		ptr = dereference_function_descriptor(ptr);


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