cregit-Linux how code gets into the kernel

Release 4.7 tools/include/linux/err.h

#ifndef __TOOLS_LINUX_ERR_H

#define __TOOLS_LINUX_ERR_H

#include <linux/compiler.h>
#include <linux/types.h>

#include <asm/errno.h>

/*
 * Original kernel header comment:
 *
 * Kernel pointers have redundant information, so we can use a
 * scheme where we can return either an error code or a normal
 * pointer with the same return value.
 *
 * This should be a per-architecture thing, to allow different
 * error and pointer decisions.
 *
 * Userspace note:
 * The same principle works for userspace, because 'error' pointers
 * fall down to the unused hole far from user space, as described
 * in Documentation/x86/x86_64/mm.txt for x86_64 arch:
 *
 * 0000000000000000 - 00007fffffffffff (=47 bits) user space, different per mm hole caused by [48:63] sign extension
 * ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
 *
 * It should be the same case for other architectures, because
 * this code is used in generic kernel code.
 */

#define MAX_ERRNO	4095


#define IS_ERR_VALUE(x) unlikely((x) >= (unsigned long)-MAX_ERRNO)


static inline void * __must_check ERR_PTR(long error_) { return (void *) error_; }

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static inline long __must_check PTR_ERR(__force const void *ptr) { return (long) ptr; }

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static inline bool __must_check IS_ERR(__force const void *ptr) { return IS_ERR_VALUE((unsigned long)ptr); }

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#endif /* _LINUX_ERR_H */

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