4:27 a.m.
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?
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.
>