arch/arm/kernel/atags.c

#include <linux/slab.h>
#include <linux/proc_fs.h>
#include <asm/setup.h>
#include <asm/types.h>
#include <asm/page.h>

struct buffer {
	size_t size;
	char data[];
};

static int
read_buffer(char* page, char** start, off_t off, int count,
	int* eof, void* data)
{
	struct buffer *buffer = (struct buffer *)data;

	if (off >= buffer->size) {
		*eof = 1;
		return 0;
	}

	count = min((int) (buffer->size - off), count);

	memcpy(page, &buffer->data[off], count);

	return count;
}

#define BOOT_PARAMS_SIZE 1536
static char __initdata atags_copy[BOOT_PARAMS_SIZE];

void __init save_atags(const struct tag *tags)
{
	memcpy(atags_copy, tags, sizeof(atags_copy));
}

static int __init init_atags_procfs(void)
{
	/*
	 * This cannot go into save_atags() because kmalloc and proc don't work
	 * yet when it is called.
	 */
	struct proc_dir_entry *tags_entry;
	struct tag *tag = (struct tag *)atags_copy;
	struct buffer *b;
	size_t size;

	if (tag->hdr.tag != ATAG_CORE) {
		printk(KERN_INFO "No ATAGs?");
		return -EINVAL;
	}

	for (; tag->hdr.size; tag = tag_next(tag))
		;

	/* include the terminating ATAG_NONE */
	size = (char *)tag - atags_copy + sizeof(struct tag_header);

	WARN_ON(tag->hdr.tag != ATAG_NONE);

	b = kmalloc(sizeof(*b) + size, GFP_KERNEL);
	if (!b)
		goto nomem;

	b->size = size;
	memcpy(b->data, atags_copy, size);

	tags_entry = create_proc_read_entry("atags", 0400,
			NULL, read_buffer, b);

	if (!tags_entry)
		goto nomem;

	return 0;

nomem:
	kfree(b);
	printk(KERN_ERR "Exporting ATAGs: not enough memory\n");

	return -ENOMEM;
}
arch_initcall(init_atags_procfs);