在看Linux內核源碼的時候，經常會遇到IS_ERR，比如在 linux/arch/arm/kernel/sys_arm.c中
asmlinkage int sys_execve(char __user *filenamei, char __user * __user *argv,
char __user * __user *envp, struct pt_regs *regs)
{
int error;
char * filename;
filename = getname(filenamei);
error = PTR_ERR(filename);
if (IS_ERR(filename))
goto out;
error = do_execve(filename, argv, envp, regs);
putname(filename);
out:
return error;
}
IS_ERR宏定義在include/linux/err.h，如下所示：
#ifndef _LINUX_ERR_H
#define _LINUX_ERR_H
#include <linux/compiler.h>
#include <asm/errno.h>
/*
* Kernel pointers have redundant information, so we can use a
* scheme where we can return either an error code or a dentry
* pointer with the same return value.
*
* This should be a per-architecture thing, to allow different
* error and pointer decisions.
*/
#define IS_ERR_VALUE(x) unlikely((x) > (unsigned long)-1000L)
static inline void *ERR_PTR(long error)
{
return (void *) error;
}
static inline long PTR_ERR(const void *ptr)
{
return (long) ptr;
}
static inline long IS_ERR(const void *ptr)
{
return IS_ERR_VALUE((unsigned long)ptr);
}
#endif /* _LINUX_ERR_H */
