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kernel.h: move PTR_IF() and u64_to_user_ptr() to util_macros.h

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While the natural choice of PTR_IF() is kconfig.h, the latter is too broad
to include C code and actually the macro was moved out from there in the
past.  But kernel.h is neither a good choice for that.  Move it to
util_macros.h.  Do the same for u64_to_user_ptr().

While moving, add necessary documentation.

Link: https://lkml.kernel.org/r/20250324105228.775784-3-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Alexandru Ardelean <aardelean@baylibre.com>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Andy Shevchenko 2025-03-24 12:50:25 +02:00 committed by Andrew Morton
parent 4ef5211ee6
commit 029c896c41
2 changed files with 67 additions and 9 deletions
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10
include/linux/kernel.h
View File

@ -33,6 +33,7 @@
#include <linux/sprintf.h>
#include <linux/static_call_types.h>
#include <linux/instruction_pointer.h>
#include <linux/util_macros.h>
#include <linux/wordpart.h>
#include <asm/byteorder.h>
@ -41,15 +42,6 @@
#define STACK_MAGIC 0xdeadbeef
#define PTR_IF(cond, ptr) ((cond) ? (ptr) : NULL)
#define u64_to_user_ptr(x) ( \
{ \
typecheck(u64, (x)); \
(void __user *)(uintptr_t)(x); \
} \
)
struct completion;
struct user;

66
include/linux/util_macros.h
View File

@ -79,6 +79,72 @@
(__fc_i); \
})
/**
* PTR_IF - evaluate to @ptr if @cond is true, or to NULL otherwise.
* @cond: A conditional, usually in a form of IS_ENABLED(CONFIG_FOO)
* @ptr: A pointer to assign if @cond is true.
*
* PTR_IF(IS_ENABLED(CONFIG_FOO), ptr) evaluates to @ptr if CONFIG_FOO is set
* to 'y' or 'm', or to NULL otherwise. The (ptr) argument must be a pointer.
*
* The macro can be very useful to help compiler dropping dead code.
*
* For instance, consider the following::
*
* #ifdef CONFIG_FOO_SUSPEND
* static int foo_suspend(struct device *dev)
* {
* ...
* }
* #endif
*
* static struct pm_ops foo_ops = {
* #ifdef CONFIG_FOO_SUSPEND
* .suspend = foo_suspend,
* #endif
* };
*
* While this works, the foo_suspend() macro is compiled conditionally,
* only when CONFIG_FOO_SUSPEND is set. This is problematic, as there could
* be a build bug in this function, we wouldn't have a way to know unless
* the configuration option is set.
*
* An alternative is to declare foo_suspend() always, but mark it
* as __maybe_unused. This works, but the __maybe_unused attribute
* is required to instruct the compiler that the function may not
* be referenced anywhere, and is safe to remove without making
* a fuss about it. This makes the programmer responsible for tagging
* the functions that can be garbage-collected.
*
* With the macro it is possible to write the following:
*
* static int foo_suspend(struct device *dev)
* {
* ...
* }
*
* static struct pm_ops foo_ops = {
* .suspend = PTR_IF(IS_ENABLED(CONFIG_FOO_SUSPEND), foo_suspend),
* };
*
* The foo_suspend() function will now be automatically dropped by the
* compiler, and it does not require any specific attribute.
*/
#define PTR_IF(cond, ptr) ((cond) ? (ptr) : NULL)
/**
* to_user_ptr - cast a pointer passed as u64 from user space to void __user *
* @x: The u64 value from user space, usually via IOCTL
*
* to_user_ptr() simply casts a pointer passed as u64 from user space to void
* __user * correctly. Using this lets us get rid of all the tiresome casts.
*/
#define u64_to_user_ptr(x) \
({ \
typecheck(u64, (x)); \
(void __user *)(uintptr_t)(x); \
})
/**
* is_insidevar - check if the @ptr points inside the @var memory range.
* @ptr: the pointer to a memory address.