drivers/video/fb_defio.c

/*
 *  linux/drivers/video/fb_defio.c
 *
 *  Copyright (C) 2006 Jaya Kumar
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License. See the file COPYING in the main directory of this archive
 * for more details.
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/vmalloc.h>
#include <linux/delay.h>
#include <linux/interrupt.h>
#include <linux/fb.h>
#include <linux/list.h>

/* to support deferred IO */
#include <linux/rmap.h>
#include <linux/pagemap.h>

struct page *fb_deferred_io_page(struct fb_info *info, unsigned long offs)
{
	void *screen_base = (void __force *) info->screen_base;
	struct page *page;

	if (is_vmalloc_addr(screen_base + offs))
		page = vmalloc_to_page(screen_base + offs);
	else
		page = pfn_to_page((info->fix.smem_start + offs) >> PAGE_SHIFT);

	return page;
}

/* this is to find and return the vmalloc-ed fb pages */
static int fb_deferred_io_fault(struct vm_area_struct *vma,
				struct vm_fault *vmf)
{
	unsigned long offset;
	struct page *page;
	struct fb_info *info = vma->vm_private_data;

	offset = vmf->pgoff << PAGE_SHIFT;
	if (offset >= info->fix.smem_len)
		return VM_FAULT_SIGBUS;

	page = fb_deferred_io_page(info, offset);
	if (!page)
		return VM_FAULT_SIGBUS;

	get_page(page);

	if (vma->vm_file)
		page->mapping = vma->vm_file->f_mapping;
	else
		printk(KERN_ERR "no mapping available\n");

	BUG_ON(!page->mapping);
	page->index = vmf->pgoff;

	vmf->page = page;
	return 0;
}

int fb_deferred_io_fsync(struct file *file, int datasync)
{
	struct fb_info *info = file->private_data;

	/* Skip if deferred io is compiled-in but disabled on this fbdev */
	if (!info->fbdefio)
		return 0;

	/* Kill off the delayed work */
	cancel_rearming_delayed_work(&info->deferred_work);

	/* Run it immediately */
	return schedule_delayed_work(&info->deferred_work, 0);
}
EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);

/* vm_ops->page_mkwrite handler */
static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
				  struct vm_fault *vmf)
{
	struct page *page = vmf->page;
	struct fb_info *info = vma->vm_private_data;
	struct fb_deferred_io *fbdefio = info->fbdefio;
	struct page *cur;

	/* this is a callback we get when userspace first tries to
	write to the page. we schedule a workqueue. that workqueue
	will eventually mkclean the touched pages and execute the
	deferred framebuffer IO. then if userspace touches a page
	again, we repeat the same scheme */

	/* protect against the workqueue changing the page list */
	mutex_lock(&fbdefio->lock);

	/* we loop through the pagelist before adding in order
	to keep the pagelist sorted */
	list_for_each_entry(cur, &fbdefio->pagelist, lru) {
		/* this check is to catch the case where a new
		process could start writing to the same page
		through a new pte. this new access can cause the
		mkwrite even when the original ps's pte is marked
		writable */
		if (unlikely(cur == page))
			goto page_already_added;
		else if (cur->index > page->index)
			break;
	}

	list_add_tail(&page->lru, &cur->lru);

page_already_added:
	mutex_unlock(&fbdefio->lock);

	/* come back after delay to process the deferred IO */
	schedule_delayed_work(&info->deferred_work, fbdefio->delay);
	return 0;
}

static const struct vm_operations_struct fb_deferred_io_vm_ops = {
	.fault		= fb_deferred_io_fault,
	.page_mkwrite	= fb_deferred_io_mkwrite,
};

static int fb_deferred_io_set_page_dirty(struct page *page)
{
	if (!PageDirty(page))
		SetPageDirty(page);
	return 0;
}

static const struct address_space_operations fb_deferred_io_aops = {
	.set_page_dirty = fb_deferred_io_set_page_dirty,
};

static int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
{
	vma->vm_ops = &fb_deferred_io_vm_ops;
	vma->vm_flags |= ( VM_RESERVED | VM_DONTEXPAND );
	if (!(info->flags & FBINFO_VIRTFB))
		vma->vm_flags |= VM_IO;
	vma->vm_private_data = info;
	return 0;
}

/* workqueue callback */
static void fb_deferred_io_work(struct work_struct *work)
{
	struct fb_info *info = container_of(work, struct fb_info,
						deferred_work.work);
	struct fb_deferred_io *fbdefio = info->fbdefio;
	struct page *page, *tmp_page;
	struct list_head *node, *tmp_node;
	struct list_head non_dirty;

	INIT_LIST_HEAD(&non_dirty);

	/* here we mkclean the pages, then do all deferred IO */
	mutex_lock(&fbdefio->lock);
	list_for_each_entry_safe(page, tmp_page, &fbdefio->pagelist, lru) {
		lock_page(page);
		/*
		 * The workqueue callback can be triggered after a
		 * ->page_mkwrite() call but before the PTE has been marked
		 * dirty. In this case page_mkclean() won't "rearm" the page.
		 *
		 * To avoid this, remove those "non-dirty" pages from the
		 * pagelist before calling the driver's callback, then add
		 * them back to get processed on the next work iteration.
		 * At that time, their PTEs will hopefully be dirty for real.
		 */
		if (!page_mkclean(page))
			list_move_tail(&page->lru, &non_dirty);
		unlock_page(page);
	}

	/* driver's callback with pagelist */
	fbdefio->deferred_io(info, &fbdefio->pagelist);

	/* clear the list... */
	list_for_each_safe(node, tmp_node, &fbdefio->pagelist) {
		list_del(node);
	}
	/* ... and add back the "non-dirty" pages to the list */
	list_splice_tail(&non_dirty, &fbdefio->pagelist);
	mutex_unlock(&fbdefio->lock);
}

void fb_deferred_io_init(struct fb_info *info)
{
	struct fb_deferred_io *fbdefio = info->fbdefio;

	BUG_ON(!fbdefio);
	mutex_init(&fbdefio->lock);
	info->fbops->fb_mmap = fb_deferred_io_mmap;
	INIT_DELAYED_WORK(&info->deferred_work, fb_deferred_io_work);
	INIT_LIST_HEAD(&fbdefio->pagelist);
	if (fbdefio->delay == 0) /* set a default of 1 s */
		fbdefio->delay = HZ;
}
EXPORT_SYMBOL_GPL(fb_deferred_io_init);

void fb_deferred_io_open(struct fb_info *info,
			 struct inode *inode,
			 struct file *file)
{
	file->f_mapping->a_ops = &fb_deferred_io_aops;
}
EXPORT_SYMBOL_GPL(fb_deferred_io_open);

void fb_deferred_io_cleanup(struct fb_info *info)
{
	struct fb_deferred_io *fbdefio = info->fbdefio;
	struct list_head *node, *tmp_node;
	struct page *page;
	int i;

	BUG_ON(!fbdefio);
	cancel_delayed_work(&info->deferred_work);
	flush_scheduled_work();

	/*  the list may have still some non-dirty pages at this point */
	mutex_lock(&fbdefio->lock);
	list_for_each_safe(node, tmp_node, &fbdefio->pagelist) {
		list_del(node);
	}
	mutex_unlock(&fbdefio->lock);

	/* clear out the mapping that we setup */
	for (i = 0 ; i < info->fix.smem_len; i += PAGE_SIZE) {
		page = fb_deferred_io_page(info, i);
		page->mapping = NULL;
	}

	info->fbops->fb_mmap = NULL;
	mutex_destroy(&fbdefio->lock);
}
EXPORT_SYMBOL_GPL(fb_deferred_io_cleanup);

MODULE_LICENSE("GPL");