diff options
Diffstat (limited to 'include/linux/util_macros.h')
| -rw-r--r-- | include/linux/util_macros.h | 152 |
1 files changed, 137 insertions, 15 deletions
diff --git a/include/linux/util_macros.h b/include/linux/util_macros.h index 72299f261b25..9373962aade9 100644 --- a/include/linux/util_macros.h +++ b/include/linux/util_macros.h @@ -2,18 +2,25 @@ #ifndef _LINUX_HELPER_MACROS_H_ #define _LINUX_HELPER_MACROS_H_ -#define __find_closest(x, a, as, op) \ -({ \ - typeof(as) __fc_i, __fc_as = (as) - 1; \ - typeof(x) __fc_x = (x); \ - typeof(*a) const *__fc_a = (a); \ - for (__fc_i = 0; __fc_i < __fc_as; __fc_i++) { \ - if (__fc_x op DIV_ROUND_CLOSEST(__fc_a[__fc_i] + \ - __fc_a[__fc_i + 1], 2)) \ - break; \ - } \ - (__fc_i); \ -}) +#include <linux/compiler_attributes.h> +#include <linux/math.h> +#include <linux/typecheck.h> +#include <linux/stddef.h> + +/** + * for_each_if - helper for handling conditionals in various for_each macros + * @condition: The condition to check + * + * Typical use:: + * + * #define for_each_foo_bar(x, y) \' + * list_for_each_entry(x, y->list, head) \' + * for_each_if(x->something == SOMETHING) + * + * The for_each_if() macro makes the use of for_each_foo_bar() less error + * prone. + */ +#define for_each_if(condition) if (!(condition)) {} else /** * find_closest - locate the closest element in a sorted array @@ -23,8 +30,27 @@ * @as: Size of 'a'. * * Returns the index of the element closest to 'x'. + * Note: If using an array of negative numbers (or mixed positive numbers), + * then be sure that 'x' is of a signed-type to get good results. */ -#define find_closest(x, a, as) __find_closest(x, a, as, <=) +#define find_closest(x, a, as) \ +({ \ + typeof(as) __fc_i, __fc_as = (as) - 1; \ + long __fc_mid_x, __fc_x = (x); \ + long __fc_left, __fc_right; \ + typeof(*a) const *__fc_a = (a); \ + for (__fc_i = 0; __fc_i < __fc_as; __fc_i++) { \ + __fc_mid_x = (__fc_a[__fc_i] + __fc_a[__fc_i + 1]) / 2; \ + if (__fc_x <= __fc_mid_x) { \ + __fc_left = __fc_x - __fc_a[__fc_i]; \ + __fc_right = __fc_a[__fc_i + 1] - __fc_x; \ + if (__fc_right < __fc_left) \ + __fc_i++; \ + break; \ + } \ + } \ + (__fc_i); \ +}) /** * find_closest_descending - locate the closest element in a sorted array @@ -34,8 +60,104 @@ * @as: Size of 'a'. * * Similar to find_closest() but 'a' is expected to be sorted in descending - * order. + * order. The iteration is done in reverse order, so that the comparison + * of '__fc_right' & '__fc_left' also works for unsigned numbers. + */ +#define find_closest_descending(x, a, as) \ +({ \ + typeof(as) __fc_i, __fc_as = (as) - 1; \ + long __fc_mid_x, __fc_x = (x); \ + long __fc_left, __fc_right; \ + typeof(*a) const *__fc_a = (a); \ + for (__fc_i = __fc_as; __fc_i >= 1; __fc_i--) { \ + __fc_mid_x = (__fc_a[__fc_i] + __fc_a[__fc_i - 1]) / 2; \ + if (__fc_x <= __fc_mid_x) { \ + __fc_left = __fc_x - __fc_a[__fc_i]; \ + __fc_right = __fc_a[__fc_i - 1] - __fc_x; \ + if (__fc_right < __fc_left) \ + __fc_i--; \ + break; \ + } \ + } \ + (__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. + * @var: the variable which address and size identify the memory range. + * + * Evaluates to true if the address in @ptr lies within the memory + * range allocated to @var. */ -#define find_closest_descending(x, a, as) __find_closest(x, a, as, >=) +#define is_insidevar(ptr, var) \ + ((uintptr_t)(ptr) >= (uintptr_t)(var) && \ + (uintptr_t)(ptr) < (uintptr_t)(var) + sizeof(var)) #endif |