linux-kernel - HugeTLB: Driver example

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Message-ID: <202cde0e0909132230y52b805a4i8792f2e287b01acb@mail.gmail.com>
Date:	Mon, 14 Sep 2009 17:30:12 +1200
From:	Alexey Korolev <akorolex@...il.com>
To:	Mel Gorman <mel@....ul.ie>, Eric Munson <linux-mm@...bm.net>,
	Alexey Korolev <akorolev@...radead.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: HugeTLB: Driver example

There is an example of simple driver which provides huge pages mapping
for user level applications. The  procedure for mapping of huge pages
to userspace by the driver is:

1. Create a hugetlb file on vfs mount of hugetlbfs (h_file)

2. File operations of /dev/hpage_map do the following:
In file open we  associate mappings of /dev/xxx with the file on
hugetlbfs (like it is done in ipc/shm.c)
       file->f_mapping = h_file->f_mapping;
In get_unmapped_area we should tell about addressing constraints in
case of huge pages by calling hugetlbfs procedures. (as in ipc/shm.c)
       return get_unmapped_area(h_file, addr, len, pgoff, flags);

3 In mmap get huge page in order to DMA or for something else
(hugetlb_get_user_page call).
..................
4 Remove hugetlbfs file

---
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/hugetlb.h>
#include <linux/pagevec.h>
#include <linux/miscdevice.h>
#include <asm/io.h>
#include <asm/ioctl.h>

#define HFILE_SIZE 16UL*1024*1024
static struct file	*h_file;

static int hpage_map_mmap(struct file *file, struct vm_area_struct *vma)
{
	int ret;
	struct page *page;
	struct hstate *h;
	unsigned long addr = vma->vm_start;

	if ((ret = h_file->f_op->mmap(h_file, vma)))
	    return ret;

	h = hstate_file(h_file);
	
	while (addr < vma->vm_end) {
		page = hugetlb_get_user_page(vma, addr);
		if (IS_ERR(page))
		        return -EFAULT;
		addr += huge_page_size(h);
		/* Add code to configure DMA here */
	}
	return 0;
}

static unsigned long hpage_map_get_unmapped_area(struct file *file,
	unsigned long addr, unsigned long len, unsigned long pgoff,
	unsigned long flags)
{
	/* Tell about addressing constrains in case of huge pages,
	 * hugetlbfs knows how to do this */
	return get_unmapped_area(h_file, addr, len, pgoff, flags);
}
static int hpage_map_open(struct inode * inode, struct file * file)
{
	/* Associate mappings of /dev/xxx with the file on hugetlbfs
	 * like it is done in ipc/shm.c */
	file->f_mapping = h_file->f_mapping;
	return 0;
}

/*
 * The file operations for /dev/hpage_map
 */
static const struct file_operations hpage_map_fops = {
	.owner		= THIS_MODULE,
	.mmap		= hpage_map_mmap,
	.open 		= hpage_map_open,
	.get_unmapped_area	= hpage_map_get_unmapped_area,
};

static struct miscdevice hpage_map_dev = {
	MISC_DYNAMIC_MINOR,
	"hpage_map",
	&hpage_map_fops
};

static int __init
hpage_map_init(void)
{
	int ret;
	struct user_struct *user = NULL;

	/* Create the device in the /sys/class/misc directory. */
	if ((ret = misc_register(&hpage_map_dev)))
		return ret;

	/* Create file on hugetlbfs */
	h_file = hugetlb_file_setup("hpage_map_dev", HFILE_SIZE, 0, &user,
				HUGETLB_DEVBACK_INODE);
	if (IS_ERR(h_file)) {
		misc_deregister(&hpage_map_dev);
		ret = -ENOENT;
	}
	return ret;
}

module_init(hpage_map_init);

static void __exit
hpage_map_exit(void)
{
	fput(h_file);
	misc_deregister(&hpage_map_dev);
}

module_exit(hpage_map_exit);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alexey Korolev");
MODULE_DESCRIPTION("Example of driver with hugetlb mapping");
MODULE_VERSION("1.0");
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