Linux 内核源代码中的“当前”是什么？
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What is the "current" in Linux kernel source?
提问by Kahn Cse
I'm studying about Linux kernel and I have a problem.
我正在研究 Linux 内核，但遇到了问题。
I see many Linux kernel source files have current->files. So what is the current?
我看到很多 Linux 内核源文件都有current->files. 那么什么是current？
struct file *fget(unsigned int fd)
{
struct file *file;
struct files_struct *files = current->files;
rcu_read_lock();
file = fcheck_files(files, fd);
if (file) {
/* File object ref couldn't be taken */
if (file->f_mode & FMODE_PATH ||
!atomic_long_inc_not_zero(&file->f_count))
file = NULL;
}
rcu_read_unlock();
return file;
}
采纳答案by Mat
It's a pointer to the current process (i.e. the process that issued the system call).
它是指向当前进程（即发出系统调用的进程）的指针。
On x86, it's defined in arch/x86/include/current.h(similar files for other archs).
在 x86 上，它是在arch/x86/include/current.h（其他拱门的类似文件）中定义的。
#ifndef _ASM_X86_CURRENT_H
#define _ASM_X86_CURRENT_H
#include <linux/compiler.h>
#include <asm/percpu.h>
#ifndef __ASSEMBLY__
struct task_struct;
DECLARE_PER_CPU(struct task_struct *, current_task);
static __always_inline struct task_struct *get_current(void)
{
return percpu_read_stable(current_task);
}
#define current get_current()
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_CURRENT_H */
More information in Linux Device Driverschapter 2:
Linux 设备驱动程序第 2 章中的更多信息：
The current pointer refers to the user process currently executing. During the execution of a system call, such as open or read, the current process is the one that invoked the call. Kernel code can use process-specific information by using current, if it needs to do so. [...]
当前指针指的是当前正在执行的用户进程。在执行系统调用（例如 open 或 read）期间，当前进程是调用该调用的进程。如果需要，内核代码可以通过使用 current 来使用特定于进程的信息。[...]
回答by coredump
Currentis a global variable of type struct task_struct. You can find it's definition at [1].
Current是一个类型为 的全局变量struct task_struct。您可以在 [1] 中找到它的定义。
Filesis a struct files_structand it contains information of the files used by the current process.
Files是一个struct files_struct，它包含当前进程使用的文件的信息。
[1] http://students.mimuw.edu.pl/SO/LabLinux/PROCESY/ZRODLA/sched.h.html
[1] http://students.mimuw.edu.pl/SO/LabLinux/PROCESY/ZRODLA/sched.h.html
