/* -*- c-basic-offset: 8 -*- */

#include <linux/config.h>
#ifdef CONFIG_SMP
# define __SMP__
#endif
#include <asm/atomic.h>
#include <linux/kernel.h>  /* Needed for KERN_ALERT */
#include <linux/module.h>  /* Needed by all modules */
#include <linux/sched.h>

#include <linux/proc_fs.h>
#include <asm/uaccess.h>
#include <linux/poll.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>

#include "sysprof-module.h"

#include <linux/version.h>

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Soeren Sandmann (sandmann@daimi.au.dk)");

#define SAMPLES_PER_SECOND (100)
#define INTERVAL (HZ / SAMPLES_PER_SECOND)
#define N_TRACES 256

static SysprofStackTrace	stack_traces[N_TRACES];
static SysprofStackTrace *	head = &stack_traces[0];
static SysprofStackTrace *	tail = &stack_traces[0];
DECLARE_WAIT_QUEUE_HEAD (wait_for_trace);
DECLARE_WAIT_QUEUE_HEAD (wait_for_exit);

typedef void (* TimeoutFunc)(unsigned long data);
static void on_timer(unsigned long);

/*
 * Wrappers to cover up kernel differences in timer handling
 */
static struct timer_list timer;

static void
init_timeout (void)
{
	init_timer(&timer);
}

static void
remove_timeout(void)
{
	del_timer (&timer);
}

static void
add_timeout(unsigned int interval,
	    TimeoutFunc  f)
{
	timer.function = f;
	mod_timer(&timer, jiffies + INTERVAL);
}

typedef struct userspace_reader userspace_reader;
struct userspace_reader
{
	struct task_struct *task;
	unsigned long user_page;
	unsigned long kernel_page;
	struct page *page;
};

static void
init_userspace_reader (userspace_reader *reader,
		       struct task_struct *task)
{
	reader->task = task;
	reader->user_page = 0;
	reader->kernel_page = 0;
	reader->page = NULL;
}

/* This is mostly cutted and pasted from ptrace.c
 * I removed some locking and stuff though. I hope it
 * wasn't important.
 */

/* Access another process' address space.
 * Source/target buffer must be kernel space, 
 * Do not walk the page table directly, use get_user_pages
 */
 
static int x_access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write)
{
	struct mm_struct *mm;
	struct vm_area_struct *vma;
	struct page *page;
	void *old_buf = buf;

	mm = tsk->mm;
	if (!mm)
		return 0;

	down_read(&mm->mmap_sem);
	/* ignore errors, just check how much was sucessfully transfered */
	while (len) {
		int bytes, ret, offset;
		void *maddr;

		ret = get_user_pages(tsk, mm, addr, 1,
				write, 1, &page, &vma);
		if (ret <= 0)
			break;

		bytes = len;
		offset = addr & (PAGE_SIZE-1);
		if (bytes > PAGE_SIZE-offset)
			bytes = PAGE_SIZE-offset;

#if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,11)
		
		flush_cache_page(vma, addr);

#endif
		
		maddr = kmap(page);
		if (write) {
			copy_to_user_page(vma, page, addr,
					  maddr + offset, buf, bytes);
			set_page_dirty_lock(page);
		} else {
			copy_from_user_page(vma, page, addr,
					    buf, maddr + offset, bytes);
		}
		kunmap(page);
		page_cache_release(page);
		len -= bytes;
		buf += bytes;
		addr += bytes;
	}
	up_read(&mm->mmap_sem);
	
	return buf - old_buf;
}

static int
read_user_space (userspace_reader *reader,
		 unsigned long address,
		 unsigned long *result)
{
#if 0
	unsigned long user_page = (address & PAGE_MASK);
	int res;
#endif

	return x_access_process_vm(reader->task, address, result, 4, 0);
}
#if 0
	struct task_struct *tsk, unsigned long addr, void *buf, int len, int write);

	if (user_page == 0)
		return 0;

	if (!reader->user_page || user_page != reader->user_page) {
		int found;
		struct page *page;
		pte_t pte;
		
		found = get_user_pages (reader->task, reader->task->mm,
					user_page, 1, 0, 0, &page, NULL);

		if (!found)
			return 0;

		if (!pte_present (page))
			return 0;
		
		if (reader->user_page)
			kunmap (reader->page);

		reader->kernel_page = (unsigned long)kmap (page);
		reader->user_page = user_page;
		reader->page = page;
		
	}

	if (get_user (res, (int *)(reader->kernel_page + (address - user_page))) != 0)
		return 0;

	*result = res;
	
	return 1;
}
#endif

static void
done_userspace_reader (userspace_reader *reader)
{
	if (reader->user_page)
		kunmap (reader->page);
}

typedef struct StackFrame StackFrame;
struct StackFrame {
	unsigned long next;
	unsigned long return_address;
};

static int
read_frame (userspace_reader *reader, unsigned long addr, StackFrame *frame)
{
	if (!addr || !frame)
		return 0;

	frame->next = 0;
	frame->return_address = 0;
	
	if (!read_user_space (reader, addr, &(frame->next)))
		return 0;

	if (!read_user_space (reader, addr + 4, &(frame->return_address)))
		return 0;

	return 1;
}

static void
generate_stack_trace(struct task_struct *task,
		     SysprofStackTrace *trace)
{
#ifdef CONFIG_HIGHMEM
#  define START_OF_STACK 0xFF000000
#else
#  define START_OF_STACK 0xBFFFFFFF
#endif
	struct pt_regs *regs = ((struct pt_regs *) (THREAD_SIZE + (unsigned long) task->thread_info)) - 1;
	StackFrame frame;
	unsigned long addr;
	userspace_reader reader;
	int i;
	
	memset(trace, 0, sizeof (SysprofStackTrace));
	
	trace->pid = task->pid;
	trace->truncated = 0;

	trace->addresses[0] = (void *)regs->eip;

	i = 1;

	addr = regs->ebp;

	init_userspace_reader (&reader, task);
	while (i < SYSPROF_MAX_ADDRESSES && read_frame (&reader, addr, &frame)  &&
	       addr < START_OF_STACK && addr >= regs->esp) {
		
		trace->addresses[i++] = (void *)frame.return_address;
		addr = frame.next;
	}
	done_userspace_reader (&reader);
	
	trace->n_addresses = i;
	if (i == SYSPROF_MAX_ADDRESSES)
		trace->truncated = 1;
	else
		trace->truncated = 0;
}

struct work_struct work;

DECLARE_WAIT_QUEUE_HEAD (wait_to_be_scanned);

static void
do_generate (void *data)
{
	struct task_struct *task = data;
	struct task_struct *g, *p;

	/* Make sure the thread still exists */
	/* FIXME: this is probably not necessary anymore, now that
	 * we make the process sleep
	 */
	do_each_thread (g, p) {
		if (p == task) {
			generate_stack_trace(task, head);

			if (head++ == &stack_traces[N_TRACES - 1])
				head = &stack_traces[0];
			
			wake_up (&wait_for_trace);
			wake_up_process (task);

			goto out;
		}
	} while_each_thread (g, p);

 out:
	add_timeout (INTERVAL, on_timer);
}

static void
on_timer(unsigned long dong)
{
#if 0
	static const int cpu_profiler = 1; /* set to 0 to profile disk */

	if (p->state == (cpu_profiler? TASK_RUNNING : TASK_UNINTERRUPTIBLE))
		;
#endif

	if (current && current->state == TASK_RUNNING && current->pid != 0) {
		INIT_WORK (&work, do_generate, current);
		
		set_current_state (TASK_UNINTERRUPTIBLE);
		
		schedule_work (&work);
	}
	else {
		add_timeout (INTERVAL, on_timer);
	}
}

static int
procfile_read(char *buffer, 
	      char **buffer_location, 
	      off_t offset, 
	      int buffer_len,
	      int *eof,
	      void *data)
{
	if (head == tail)
		return -EWOULDBLOCK;
	wait_event_interruptible (wait_for_trace, head != tail);
	*buffer_location = (char *)tail;
	if (tail++ == &stack_traces[N_TRACES - 1])
		tail = &stack_traces[0];
	return sizeof (SysprofStackTrace);
}

struct proc_dir_entry *trace_proc_file;
static unsigned int
procfile_poll(struct file *filp, poll_table *poll_table)
{
	if (head != tail) {
		return POLLIN | POLLRDNORM;
	}
	poll_wait(filp, &wait_for_trace, poll_table);
	if (head != tail) {
		return POLLIN | POLLRDNORM;
	}
	return 0;
}

int
init_module(void)
{
	trace_proc_file =
		create_proc_entry ("sysprof-trace", S_IFREG | S_IRUGO, &proc_root);
	
	if (!trace_proc_file)
		return 1;
	
	trace_proc_file->read_proc = procfile_read;
	trace_proc_file->proc_fops->poll = procfile_poll;
	trace_proc_file->size = sizeof (SysprofStackTrace);
	
	init_timeout();
	
	add_timeout(INTERVAL, on_timer);
	
	printk(KERN_ALERT "starting sysprof module\n");
	
	return 0;
}

void
cleanup_module(void)
{
	remove_timeout();
	
	remove_proc_entry("sysprof-trace", &proc_root);
	
	printk(KERN_ALERT "stopping sysprof module\n");
}