put_user() linux 内核
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put_user() linux kernel
提问by Pawan
After doing put_user(message[i], buf+i);how can I access message from user space?
完成后put_user(message[i], buf+i);如何从用户空间访问消息？
I really don't understand where the string message is to be accessed from and what I can do with it?
我真的不明白从哪里访问字符串消息以及我可以用它做什么？
采纳答案by ZelluX
put_user (x, ptr). Here xis the value to copy to user space, while ptris the destination address, in user space.
put_user (x, ptr). 这里x是复制到用户空间的值，ptr而是用户空间中的目标地址。
So in user application the message can be accessed by buf+i.
因此，在用户应用程序中，可以通过buf+i.
回答by sarnold
put_user()should only be called in the context of a process making a system call.
put_user()应该只在进行系统调用的进程的上下文中调用。
Consider an application calling ptrace(2)(see kernel/ptrace.c).
考虑一个应用程序调用ptrace(2)（请参阅 参考资料kernel/ptrace.c）。
The kernel will call into an architecture-specific ptracehelper:
内核将调用特定于体系结构的ptrace帮助程序：
SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
unsigned long, data)
{
/* arch-independent code */
/* ... */
ret = arch_ptrace(child, request, addr, data);
On the x86 platform, arch_ptrace()is defined in arch/x86/kernel/ptrace.c:
在 x86 平台上，arch_ptrace()定义在arch/x86/kernel/ptrace.c：
long arch_ptrace(struct task_struct *child, long request,
unsigned long addr, unsigned long data)
{
int ret;
unsigned long __user *datap = (unsigned long __user *)data;
switch (request) {
/* read the word at location addr in the USER area. */
case PTRACE_PEEKUSR: {
unsigned long tmp;
ret = -EIO;
if ((addr & (sizeof(data) - 1)) || addr >= sizeof(struct user))
break;
tmp = 0; /* Default return condition */
if (addr < sizeof(struct user_regs_struct))
tmp = getreg(child, addr);
else if (addr >= offsetof(struct user, u_debugreg[0]) &&
addr <= offsetof(struct user, u_debugreg[7])) {
addr -= offsetof(struct user, u_debugreg[0]);
tmp = ptrace_get_debugreg(child, addr / sizeof(data));
}
ret = put_user(tmp, datap);
break;
}
When a process calls ptrace(2)and asks to perform a PTRACE_PEEKUSR, the kernel needs to return information (ret) back to the user. The kernel uses the datappointer to a user supplied bufferto know where in the process to write the value of tmp.
当进程调用ptrace(2)并要求执行 a 时PTRACE_PEEKUSR，内核需要将信息 ( ret) 返回给用户。内核使用datap指向用户提供的缓冲区的指针来知道在进程中的何处写入 的值tmp。
Almost every case of calling put_user()will be initiated by a userland process. Sending signals to userspace is an obvious difference, where the kernel initiates sending the signal, but the kernel has code (see arch/x86/kernel/signal.cfunction __setup_frame()) to find the stack frame and write into it the need to handle a signal.
几乎所有的调用情况put_user()都会由用户态进程发起。向用户空间发送信号是一个明显的区别，内核开始发送信号，但内核有代码（见arch/x86/kernel/signal.c函数__setup_frame()）来查找堆栈帧并将处理信号的需要写入其中。
So, after a long-winded discussion: You will access your data in your process via whatever buffer you gave to the kernel to write into-- it could be a buffer for a driver-specific ioctl(2), it could be a buffer argument to a new system call you create, you have a lot of choices.
因此，经过冗长的讨论：您将通过给内核写入的任何缓冲区访问进程中的数据——它可以是特定于驱动程序的缓冲区ioctl(2)，也可以是新的缓冲区参数您创建的系统调用，您有很多选择。
