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

Started byAndy Shevchenko <andriy.shevchenko@linux.intel.com>
First post2016-04-07 18:50 +0200
Last post2016-04-09 01:50 +0200
Articles 4 — 3 participants

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  Re: [PATCH v1 06/10] device property: switch to use UUID API Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2016-04-07 18:50 +0200
    Re: [PATCH v1 06/10] device property: switch to use UUID API "Huang\, Ying" <ying.huang@intel.com> - 2016-04-08 03:30 +0200
      Re: [PATCH v1 06/10] device property: switch to use UUID API Andy Shevchenko <andriy.shevchenko@linux.intel.com> - 2016-04-08 12:10 +0200
        Re: [PATCH v1 06/10] device property: switch to use UUID API huang ying <huang.ying.caritas@gmail.com> - 2016-04-09 01:50 +0200

#1373556 — Re: [PATCH v1 06/10] device property: switch to use UUID API

FromAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Date2016-04-07 18:50 +0200
SubjectRe: [PATCH v1 06/10] device property: switch to use UUID API
Message-ID<rlli3-6NG-37@gated-at.bofh.it>
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@linux.intel.com>
Intel Finland Oy

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#1373927

From"Huang\, Ying" <ying.huang@intel.com>
Date2016-04-08 03:30 +0200
Message-ID<rltph-4oU-5@gated-at.bofh.it>
In reply to#1373556
Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:

> 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.

You can take a look at the drivers/acpi/apei/erst.c for uuid_le_cmp
usage.

#define CPER_CREATOR_PSTORE                                             \
        UUID_LE(0x75a574e3, 0x5052, 0x4b29, 0x8a, 0x8e, 0xbe, 0x2c,     \
                0x64, 0x90, 0xb8, 0x9d)

        if (uuid_le_cmp(rcd->hdr.creator_id, CPER_CREATOR_PSTORE) != 0)
                goto skip;

Looks better?

This is the typical use case in mind when I write the uuid.h.

As for uuid_le_cmp usage in drivers/acpi/apei/ghes.c,

		if (!uuid_le_cmp(*(uuid_le *)gdata->section_type,
				 CPER_SEC_PLATFORM_MEM)) {

The code looks not good mainly because acpi_hest_generic_data is not
defined with uuid_le in mind.

struct acpi_hest_generic_data {
	u8 section_type[16];
	u32 error_severity;
	u16 revision;
	u8 validation_bits;
	u8 flags;
	u32 error_data_length;
	u8 fru_id[16];
	u8 fru_text[20];
};

If section_type was defined as uuid_le instead of u8[16], the
uuid_le_cmp usage would look better.  So I suggest to use uuid_le/be in
data structure definition in new code if possible.

Best Regards,
Huang, Ying

>> > 
>> > > 
>> > > +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.
>>

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#1374122

FromAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Date2016-04-08 12:10 +0200
Message-ID<rlBwu-2b5-7@gated-at.bofh.it>
In reply to#1373927
On Fri, 2016-04-08 at 09:27 +0800, Huang, Ying wrote:
> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
> 
> > 
> > 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.
> You can take a look at the drivers/acpi/apei/erst.c for uuid_le_cmp
> usage.
> 
> #define
> CPER_CREATOR_PSTORE                                             \
>         UUID_LE(0x75a574e3, 0x5052, 0x4b29, 0x8a, 0x8e, 0xbe,
> 0x2c,     \
>                 0x64, 0x90, 0xb8, 0x9d)
> 
>         if (uuid_le_cmp(rcd->hdr.creator_id, CPER_CREATOR_PSTORE) !=
> 0)
>                 goto skip;
> 
> Looks better?

I don't quite understand the issues with 

if (uuid_le_cmp(&rcd->hdr.creator_id, &CPER_CREATOR_PSTORE) != 0)

or, like I mentioned previously, we may introduce _cmp_p() and use like

if (uuid_le_cmp_p(&rcd->hdr.creator_id, CPER_CREATOR_PSTORE) != 0)

if it looks better (again, I don't know if compiler is going to copy the last argument).

> 
> This is the typical use case in mind when I write the uuid.h.
> 
> As for uuid_le_cmp usage in drivers/acpi/apei/ghes.c,
> 
> 		if (!uuid_le_cmp(*(uuid_le *)gdata->section_type,
> 				 CPER_SEC_PLATFORM_MEM)) {

Ditto

if (!uuid_le_cmp_p((uuid_le *)gdata->section_type,
CPER_SEC_PLATFORM_MEM)) {

> 
> The code looks not good mainly because acpi_hest_generic_data is not
> defined with uuid_le in mind.
> 
> struct acpi_hest_generic_data {
> 	u8 section_type[16];
> 	u32 error_severity;
> 	u16 revision;
> 	u8 validation_bits;
> 	u8 flags;
> 	u32 error_data_length;
> 	u8 fru_id[16];
> 	u8 fru_text[20];
> };
> 
> If section_type was defined as uuid_le instead of u8[16], the
> uuid_le_cmp usage would look better.  So I suggest to use uuid_le/be
> in
> data structure definition in new code if possible.

This is understandable for such structures, but we might get a UUID from
a buffer which is pointer to u8. It's not possible to convert to uuid_*
since it's too generic stuff and might require to introduce
ACPI_TYPE_UUID with standardization and all necessary work. Apparently
not the shortest way.

> 
> Best Regards,
> Huang, Ying
> 
> > 
> > > 
> > > > 
> > > > 
> > > > > 
> > > > > 
> > > > > +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@linux.intel.com>
Intel Finland Oy

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#1374539

Fromhuang ying <huang.ying.caritas@gmail.com>
Date2016-04-09 01:50 +0200
Message-ID<rlOk3-4h2-29@gated-at.bofh.it>
In reply to#1374122
On Fri, Apr 8, 2016 at 6:00 PM, Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
> On Fri, 2016-04-08 at 09:27 +0800, Huang, Ying wrote:
>> Andy Shevchenko <andriy.shevchenko@linux.intel.com> writes:
>>
>> >
>> > 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.
>> You can take a look at the drivers/acpi/apei/erst.c for uuid_le_cmp
>> usage.
>>
>> #define
>> CPER_CREATOR_PSTORE                                             \
>>         UUID_LE(0x75a574e3, 0x5052, 0x4b29, 0x8a, 0x8e, 0xbe,
>> 0x2c,     \
>>                 0x64, 0x90, 0xb8, 0x9d)
>>
>>         if (uuid_le_cmp(rcd->hdr.creator_id, CPER_CREATOR_PSTORE) !=
>> 0)
>>                 goto skip;
>>
>> Looks better?
>
> I don't quite understand the issues with
>
> if (uuid_le_cmp(&rcd->hdr.creator_id, &CPER_CREATOR_PSTORE) != 0)

I tried to make uuid_le looks like a primitive data type and UUID
constant looks like primitive type constants if possible.  If we can
define data as uuid_le/be, then it will look just like that.  But if
there are too many places we cannot use uuid_le/be directly, I am OK
to convert the interface to use pointer instead.

> or, like I mentioned previously, we may introduce _cmp_p() and use like
>
> if (uuid_le_cmp_p(&rcd->hdr.creator_id, CPER_CREATOR_PSTORE) != 0)

Personally, I don't like this interface. It is better for two
parameters to have same data type.

> if it looks better (again, I don't know if compiler is going to copy the last argument).
>
>>
>> This is the typical use case in mind when I write the uuid.h.
>>
>> As for uuid_le_cmp usage in drivers/acpi/apei/ghes.c,
>>
>>               if (!uuid_le_cmp(*(uuid_le *)gdata->section_type,
>>                                CPER_SEC_PLATFORM_MEM)) {
>
> Ditto
>
> if (!uuid_le_cmp_p((uuid_le *)gdata->section_type,
> CPER_SEC_PLATFORM_MEM)) {
>
>>
>> The code looks not good mainly because acpi_hest_generic_data is not
>> defined with uuid_le in mind.
>>
>> struct acpi_hest_generic_data {
>>       u8 section_type[16];
>>       u32 error_severity;
>>       u16 revision;
>>       u8 validation_bits;
>>       u8 flags;
>>       u32 error_data_length;
>>       u8 fru_id[16];
>>       u8 fru_text[20];
>> };
>>
>> If section_type was defined as uuid_le instead of u8[16], the
>> uuid_le_cmp usage would look better.  So I suggest to use uuid_le/be
>> in
>> data structure definition in new code if possible.
>
> This is understandable for such structures, but we might get a UUID from
> a buffer which is pointer to u8. It's not possible to convert to uuid_*
> since it's too generic stuff and might require to introduce
> ACPI_TYPE_UUID with standardization and all necessary work. Apparently
> not the shortest way.

If this is just a special case that happens seldom, we can just work
around it with *(uuid_le/be *)buf.  If it is common, we can change the
interface or add a new interface.

Best Regards,
Huang, YIng

>> >
>> > >
>> > > >
>> > > >
>> > > > >
>> > > > >
>> > > > > +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@linux.intel.com>
> Intel Finland Oy
>

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