11 a.m.
On Fri, 2016-04-08 at 09:27 +0800, Huang, Ying wrote:
Andy Shevchenko <andriy.shevchenko(a)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(a)linux.intel.com>
Intel Finland Oy