linux-kernel - Re: [PATCH v1 06/10] device property: switch to use UUID API

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Message-ID: <1460047286.6620.26.camel@linux.intel.com>
Date:	Thu, 07 Apr 2016 19:41:26 +0300
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Huang Ying <ying.huang@...el.com>
Cc:	Theodore Ts'o <tytso@....edu>, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
	Jani Nikula <jani.nikula@...ux.intel.com>,
	David Airlie <airlied@...ux.ie>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	Lv Zheng <lv.zheng@...el.com>, Mark Brown <broonie@...nel.org>,
	Zhang Rui <rui.zhang@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-efi@...r.kernel.org,
	linux-api@...r.kernel.org, linux-nvdimm@...ts.01.org
Subject: Re: [PATCH v1 06/10] device property: switch to use UUID API

On Fri, 2016-02-26 at 16:11 +0200, Andy Shevchenko wrote:
> On Thu, 2016-02-18 at 01:03 +0100, Rafael J. Wysocki wrote:
> > 
> > On Wednesday, February 17, 2016 02:17:24 PM Andy Shevchenko wrote:
> > > 
> > > Switch to use a generic UUID API instead of custom approach. It
> > > allows to
> > > define UUIDs, compare them, and validate.
> []
> 

Summon initial author of the UUID library.

Summary: the API of comparison functions is rather strange. What the
point to not take pointers directly? (Moreover I hope compiler too
clever not to make a copy of constant arguments there)

I could only imagine the case you are trying to avoid temporary
variables for constants like NULL_UUID.

Issue with this is the ugliness in the users of that, in particularly
present in ACPI (drivers/acpi/apei/ghes.c).

I would like to have more clear interface for that. Perhaps we may add
something like

cmp_p(pointer, non-pointer);
cmp_pp(pointer, pointer);

to not break existing API for now.

It would be useful for many cases in the kernel.

> > 
> > > 
> > > +static const uuid_le ads_uuid =
> > > +	UUID_LE(0xdbb8e3e6, 0x5886, 0x4ba6,
> > > +		0x87, 0x95, 0x13, 0x19, 0xf5, 0x2a, 0x96, 0x6b);
> > >  
> > >  static bool acpi_enumerate_nondev_subnodes(acpi_handle scope,
> > >  					   const union
> > > acpi_object
> > > *desc,
> > > @@ -138,7 +136,7 @@ static bool
> > > acpi_enumerate_nondev_subnodes(acpi_handle scope,
> > >  		    || links->type != ACPI_TYPE_PACKAGE)
> > >  			break;
> > >  
> > > -		if (memcmp(uuid->buffer.pointer, ads_uuid,
> > > sizeof(ads_uuid)))
> > > +		if (uuid_le_cmp(*(uuid_le *)uuid->buffer.pointer,
> > > ads_uuid))
> > Maybe it's too late, but I don't quite understand the pointer
> > manipulations here.
> > 
> > I can see why you need a type conversion (although it looks ugly),
> > but why do you
> > need to dereference it too?
> The function takes that kind of type on input. The other variants are
> not compiled.
> Perhaps we better change uuid_{lb}e_cmp() first to take normal
> pointers, though I think the initial idea was to get type checking at
> compile time.
> 

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy