fb_defio.c

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/*
 *  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>

static 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, loff_t start, loff_t end, int datasync)
{
    struct fb_info *info = file->private_data;
    struct inode *inode = file->f_path.dentry->d_inode;
    int err = filemap_write_and_wait_range(inode->i_mapping, start, end);
    if (err)
        return err;

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

    mutex_lock(&inode->i_mutex);
    /* Kill off the delayed work */
    cancel_delayed_work_sync(&info->deferred_work);

    /* Run it immediately */
    err = schedule_delayed_work(&info->deferred_work, 0);
    mutex_unlock(&inode->i_mutex);
    return err;
}
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 */

    file_update_time(vma->vm_file);

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

    /* first write in this cycle, notify the driver */
    if (fbdefio->first_io && list_empty(&fbdefio->pagelist))
        fbdefio->first_io(info);

    /*
     * We want the page to remain locked from ->page_mkwrite until
     * the PTE is marked dirty to avoid page_mkclean() being called
     * before the PTE is updated, which would leave the page ignored
     * by defio.
     * Do this by locking the page here and informing the caller
     * about it with VM_FAULT_LOCKED.
     */
    lock_page(page);

    /* 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 VM_FAULT_LOCKED;
}

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_DONTEXPAND | VM_DONTDUMP;
    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 list_head *node, *next;
    struct page *cur;
    struct fb_deferred_io *fbdefio = info->fbdefio;

    /* here we mkclean the pages, then do all deferred IO */
    mutex_lock(&fbdefio->lock);
    list_for_each_entry(cur, &fbdefio->pagelist, lru) {
        lock_page(cur);
        page_mkclean(cur);
        unlock_page(cur);
    }

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

    /* clear the list */
    list_for_each_safe(node, next, &fbdefio->pagelist) {
        list_del(node);
    }
    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 page *page;
    int i;

    BUG_ON(!fbdefio);
    cancel_delayed_work_sync(&info->deferred_work);

    /* 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");