Re: [PATCH v5 RESEND 1/5] ACPI: Add acpi_pr_<level>() interfaces

[Toshi Kani <toshi.kani@hp.com>]

On Tue, 2012-11-20 at 02:17 +0100, Rafael J. Wysocki wrote:
> On Monday, November 19, 2012 09:10:58 AM Rafael J. Wysocki wrote:
> > On Tuesday, November 06, 2012 08:02:06 AM Toshi Kani 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. for hotplug operations.  acpi_pr_<level>()
> > > appends "ACPI" prefix and ACPI object path to the messages.  This
> > > improves diagnosis of hotplug operations since an error message in
> > > a log file identifies an object that caused an issue.
> > > 
> > > 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:
> > >   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 path in their messages, such as error cases.
> > > The usage model is similar to dev_<level>().  acpi_pr_<level>() can
> > > be used when device is not created/valid, which may be the case in
> > > ACPI hotplug handlers.  ACPI object path is also consistent on the
> > > platform, unlike device name that changes over hotplug operations.
> > > 
> > > ACPI drivers should use dev_<level>() when device is valid and
> > > acpi_pr_<level>() is already used by the caller in its error path.
> > > Device name provides more user friendly information.
> > > 
> > > ACPI drivers also continue to use pr_<level>() when messages do not
> > > need to specify device information, such as boot-up messages.
> > > 
> > > Note: ACPI_[WARNING|INFO|ERROR]() are intended for the ACPICA and
> > > are not associated with the kernel message level.
> > 
> > Well, the idea is generally good, but unfortunately acpi_get_name() is
> > not a cheap operation.  Namely, it takes the global namespace mutex,
> > so your acpi_printk() may be a source of serious contention on that
> > lock if used excessively from concurrent threads.
> > 
> > Do you think you can address this problem?
> > 
> > Moreover, this also means that acpi_printk() cannot be used from interrupt
> > context, so it is not a printk() replacement, which at least should be
> > documented.
> 
> Unfortunately, I lost your reply to my previous message in this thread
> due to my e-mail client malfunction.  Sorry about that.
> 
> What about calling them acpi_handle_printk() and acpi_handle_<level>,
> respectively?  Then, if it is clearly documented that those things
> acquire the global namespace mutex and are not suitable for interrupt
> context, it should be OK.

Sounds good to me.  I will update the function names and document it in
the comment and change log.

> And please take Joe's feedback into account. :-)

Yes, Joe has been great help on this patchset (Thanks Joe!).  I think
the only remaining point is the header file location, which I will reply
to your other email.

Thanks,
-Toshi