I am new to kernel programming and trying to implement a system call in linux kernel 3.19 which keeps track of the processes in a linked list. So every time the system call is invoked from user-space (by some wrapper function) a new process has to be added to that list. My system call looks something like
asmlinkage long sys_newcall(pid_t pid)
{
/*
* mytasks is the name of the structure
* kmalloc() is invoked to create an instance
*/
struct mytasks newTask = kmalloc(sizeof(struct mytasks), GFP_KERNEL);
/* various checks */
/* now adding the new instance to the list */
list_add_tail(&(newTask->list),&(mylist->list));
/* i have put list_head struct in my own structure to make use of above interface */
}
Now the mylist
variable used above should be defined global so as to maintain the list for subsequent system calls. How to accomplish that? Do I have to declare mylist
variable in linux/init/main.c
or I can simply use EXPORT_GLOBAL
. I also read about using extern but couldn't figure out where to declare and define the variable.
最好使用EXPORT_SYMBOL,因为这对于可加载模块也是可见的,并将其声明为正在使用的文件或本地头文件中
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