[v1,1/1] ACPI: NFIT: Import GUID before use

Strictly speaking the comparison between guid_t and raw buffer
is not correct. Import GUID to variable of guid_t type and then
compare.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
 drivers/acpi/nfit/core.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

On Thu, Apr 15, 2021 at 6:59 AM Andy Shevchenko
<andriy.shevchenko@linux.intel.com> wrote:
>
> Strictly speaking the comparison between guid_t and raw buffer
> is not correct. Import GUID to variable of guid_t type and then
> compare.

Hmm, what about something like the following instead, because it adds
safety. Any concerns about evaluating x twice in a macro should be
alleviated by the fact that ARRAY_SIZE() will fail the build if (x) is
not an array.

diff --git a/drivers/acpi/nfit/core.c b/drivers/acpi/nfit/core.c
index 8c5dde628405..bac01eec07a6 100644
--- a/drivers/acpi/nfit/core.c
+++ b/drivers/acpi/nfit/core.c
@@ -681,7 +681,7 @@ int nfit_spa_type(struct acpi_nfit_system_address *spa)
        int i;

        for (i = 0; i < NFIT_UUID_MAX; i++)
-               if (guid_equal(to_nfit_uuid(i), (guid_t *)&spa->range_guid))
+               if (guid_equal(to_nfit_uuid(i), cast_guid(spa->range_guid)))
                        return i;
        return -1;
 }
diff --git a/include/linux/uuid.h b/include/linux/uuid.h
index 8cdc0d3567cd..cec1dc2ab994 100644
--- a/include/linux/uuid.h
+++ b/include/linux/uuid.h
@@ -33,6 +33,9 @@ typedef struct {
 extern const guid_t guid_null;
 extern const uuid_t uuid_null;

+#define cast_guid(x) ({ BUILD_BUG_ON(ARRAY_SIZE(x) != 16); (guid_t *)&(x); })
+#define cast_uuid(x) ({ BUILD_BUG_ON(ARRAY_SIZE(x) != 16); (uuid_t *)&(x); })
+
 static inline bool guid_equal(const guid_t *u1, const guid_t *u2)
 {
        return memcmp(u1, u2, sizeof(guid_t)) == 0;

On Fri, Apr 16, 2021 at 1:58 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Fri, Apr 16, 2021 at 8:28 AM Dan Williams <dan.j.williams@intel.com> wrote:
> >
> > On Thu, Apr 15, 2021 at 6:59 AM Andy Shevchenko
> > <andriy.shevchenko@linux.intel.com> wrote:
> > >
> > > Strictly speaking the comparison between guid_t and raw buffer
> > > is not correct. Import GUID to variable of guid_t type and then
> > > compare.
> >
> > Hmm, what about something like the following instead, because it adds
> > safety. Any concerns about evaluating x twice in a macro should be
> > alleviated by the fact that ARRAY_SIZE() will fail the build if (x) is
> > not an array.
>
> ARRAY_SIZE doesn't check type.

See __must_be_array.

> I don't like hiding ugly casts like this.

See PTR_ERR, ERR_PTR, ERR_CAST.

There's nothing broken about the way the code currently stands, so I'd
rather try to find something to move the implementation forward than
sideways.

On Fri, Apr 16, 2021 at 10:34 AM Andy Shevchenko
<andy.shevchenko@gmail.com> wrote:
>
> On Fri, Apr 16, 2021 at 09:15:34AM -0700, Dan Williams wrote:
> > On Fri, Apr 16, 2021 at 1:58 AM Andy Shevchenko
> > <andy.shevchenko@gmail.com> wrote:
> > > On Fri, Apr 16, 2021 at 8:28 AM Dan Williams <dan.j.williams@intel.com> wrote:
> > > > On Thu, Apr 15, 2021 at 6:59 AM Andy Shevchenko
> > > > <andriy.shevchenko@linux.intel.com> wrote:
> > > > >
> > > > > Strictly speaking the comparison between guid_t and raw buffer
> > > > > is not correct. Import GUID to variable of guid_t type and then
> > > > > compare.
> > > >
> > > > Hmm, what about something like the following instead, because it adds
> > > > safety. Any concerns about evaluating x twice in a macro should be
> > > > alleviated by the fact that ARRAY_SIZE() will fail the build if (x) is
> > > > not an array.
> > >
> > > ARRAY_SIZE doesn't check type.
> >
> > See __must_be_array.
> >
> > > I don't like hiding ugly casts like this.
> >
> > See PTR_ERR, ERR_PTR, ERR_CAST.
>
> It's special, i.e. error pointer case. We don't handle such here.
>
> > There's nothing broken about the way the code currently stands, so I'd
> > rather try to find something to move the implementation forward than
> > sideways.
>
> Submit a patch then. I rest my case b/c I consider that ugly castings worse
> than additional API call, although it's not ideal.

It sounds like you'll NAK that patch, and I'm not too enthusiastic
about these proposed changes either because I disagree that the code
is incorrect. Is there another compromise?