Let me have time to ask some questions about Linux.
we can access user buffer within interrupt handler (kernel mode) if we tocuch segment selectors.
Like these:
mm_segment_t fs;
fs = get_fs();
set_fs(get_dsc());
call user space function .
.....
set_fs(fs);
My question is:
Can we execute(call) a function of user space within the interrupt handler?
reference site http://www.cs.unm.edu/~jotto/linux/linux.html
Something similar happens with segment selectors when an interrupt takes place. But in this case there is no assurance that the handler is executing in the context of the interested process. Suppose though that by some bit of magic the interrupt handler knows the process's pid and a buffer address. Then in the case that the handler needs to write data to the buffer we could do something like the following:
struct task_struct* pid2task(int);
void in_thehandler();
int pid;
char* user_buf;
char ch;
unsigned long pgdir;
struct task_struct *temp;
void in_thehandler()
{
temp = current_set[0];
current_set[0] = pid2task(pid);
if (!current_set[0]) {
printk("error: couldn't find process.\n");
}
else {
/* make CR3 point to this guy's page directory */
pgdir = current_set[0]->tss.cr3;
__asm__ __volatile__("movl %0,%%cr3": :"r" (pgdir));
memcpy_tofs(user_buf, &ch, 1);
}
current_set[0] = temp;
/* restore CR3 to point to the original page directory */
pgdir = current_set[0]->tss.cr3;
__asm__ __volatile__("movl %0,%%cr3": :"r" (pgdir));
}
struct task_struct* pid2task(int pid)
{
/* see the section on Virtual to Physical address translation */
}
Here, we do a bit of a context switch by finding out the task structure associated with the pid (by calling pid2task()and then loading the page directory pointer for that task into the CR3 register (the latter is the hardware's entry point to a given process's paging structures). Then we can use the _fs functions. When we are done we restore the saved context. The code for updating CR3 was lifted from the SET_PAGE_DIR macro in include/asm.
Thank you in advance
