rd.c

讲述linux的初始化过程

/*
 * ramdisk.c - Multiple RAM disk driver - gzip-loading version - v. 0.8 beta.
 * 
 * (C) Chad Page, Theodore Ts'o, et. al, 1995. 
 *
 * This RAM disk is designed to have filesystems created on it and mounted
 * just like a regular floppy disk.  
 *  
 * It also does something suggested by Linus: use the buffer cache as the
 * RAM disk data.  This makes it possible to dynamically allocate the RAM disk
 * buffer - with some consequences I have to deal with as I write this. 
 * 
 * This code is based on the original ramdisk.c, written mostly by
 * Theodore Ts'o (TYT) in 1991.  The code was largely rewritten by
 * Chad Page to use the buffer cache to store the RAM disk data in
 * 1995; Theodore then took over the driver again, and cleaned it up
 * for inclusion in the mainline kernel.
 *
 * The original CRAMDISK code was written by Richard Lyons, and
 * adapted by Chad Page to use the new RAM disk interface.  Theodore
 * Ts'o rewrote it so that both the compressed RAM disk loader and the
 * kernel decompressor uses the same inflate.c codebase.  The RAM disk
 * loader now also loads into a dynamic (buffer cache based) RAM disk,
 * not the old static RAM disk.  Support for the old static RAM disk has
 * been completely removed.
 *
 * Loadable module support added by Tom Dyas.
 *
 * Further cleanups by Chad Page ([e-mail]):
 *	Cosmetic changes in #ifdef MODULE, code movement, etc.
 * 	When the RAM disk module is removed, free the protected buffers
 * 	Default RAM disk size changed to 2.88 MB
 *
 *  Added initrd: Werner Almesberger & Hans Lermen, Feb '96
 *
 * 4/25/96 : Made RAM disk size a parameter (default is now 4 MB) 
 *		- Chad Page
 *
 * Add support for fs images split across >1 disk, Paul Gortmaker, Mar '98
 *
 * Make block size and block size shift for RAM disks a global macro
 * and set blk_size for -ENOSPC,     Werner Fink <[e-mail]>, Apr '99
 */

#include <linux/config.h>
#include <linux/sched.h>
#include <linux/minix_fs.h>
#include <linux/ext2_fs.h>
#include <linux/romfs_fs.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/hdreg.h>
#include <linux/string.h>
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/malloc.h>
#include <linux/ioctl.h>
#include <linux/fd.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/devfs_fs_kernel.h>
#include <linux/smp_lock.h>

#include <asm/system.h>
#include <asm/uaccess.h>
#include <asm/byteorder.h>

extern void wait_for_keypress(void);

/*
 * 35 has been officially registered as the RAMDISK major number, but
 * so is the original MAJOR number of 1.  We're using 1 in
 * include/linux/major.h for now
 */
#define MAJOR_NR RAMDISK_MAJOR
#include <linux/blk.h>
#include <linux/blkpg.h>

/* The RAM disk size is now a parameter */
#define NUM_RAMDISKS 16		/* This cannot be overridden (yet) */ 

#ifndef MODULE
/* We don't have to load RAM disks or gunzip them in a module. */
#define RD_LOADER
#define BUILD_CRAMDISK

void rd_load(void);
static int crd_load(struct file *fp, struct file *outfp);

#ifdef CONFIG_BLK_DEV_INITRD
static int initrd_users;
#endif
#endif

/* Various static variables go here.  Most are used only in the RAM disk code.
 */

static unsigned long rd_length[NUM_RAMDISKS];	/* Size of RAM disks in bytes   */
static int rd_hardsec[NUM_RAMDISKS];		/* Size of real blocks in bytes */
static int rd_blocksizes[NUM_RAMDISKS];		/* Size of 1024 byte blocks :)  */
static int rd_kbsize[NUM_RAMDISKS];		/* Size in blocks of 1024 bytes */
static devfs_handle_t devfs_handle;
static struct inode *rd_inode[NUM_RAMDISKS];	/* Protected device inodes */

/*
 * Parameters for the boot-loading of the RAM disk.  These are set by
 * init/main.c (from arguments to the kernel command line) or from the
 * architecture-specific setup routine (from the stored boot sector
 * information). 
 */
int rd_size = CONFIG_BLK_DEV_RAM_SIZE;		/* Size of the RAM disks */
/*
 * It would be very desiderable to have a soft-blocksize (that in the case
 * of the ramdisk driver is also the hardblocksize ;) of PAGE_SIZE because
 * doing that we'll achieve a far better MM footprint. Using a rd_blocksize of
 * BLOCK_SIZE in the worst case we'll make PAGE_SIZE/BLOCK_SIZE buffer-pages
 * unfreeable. With a rd_blocksize of PAGE_SIZE instead we are sure that only
 * 1 page will be protected. Depending on the size of the ramdisk you
 * may want to change the ramdisk blocksize to achieve a better or worse MM
 * behaviour. The default is still BLOCK_SIZE (needed by rd_load_image that
 * supposes the filesystem in the image uses a BLOCK_SIZE blocksize).
 */
int rd_blocksize = BLOCK_SIZE;			/* blocksize of the RAM disks */

#ifndef MODULE

int rd_doload;			/* 1 = load RAM disk, 0 = don't load */
int rd_prompt = 1;		/* 1 = prompt for RAM disk, 0 = don't prompt */
int rd_image_start;		/* starting block # of image */
#ifdef CONFIG_BLK_DEV_INITRD
unsigned long initrd_start, initrd_end;
int mount_initrd = 1;		/* zero if initrd should not be mounted */
int initrd_below_start_ok;

static int __init no_initrd(char *str)
{
	mount_initrd = 0;
	return 1;
}

__setup("noinitrd", no_initrd);

#endif

static int __init ramdisk_start_setup(char *str)
{
	rd_image_start = simple_strtol(str,NULL,0);
	return 1;
}

static int __init load_ramdisk(char *str)
{
	rd_doload = simple_strtol(str,NULL,0) & 3;
	return 1;
}

static int __init prompt_ramdisk(char *str)
{
	rd_prompt = simple_strtol(str,NULL,0) & 1;
	return 1;
}

static int __init ramdisk_size(char *str)
{
	rd_size = simple_strtol(str,NULL,0);
	return 1;
}

static int __init ramdisk_size2(char *str)
{
	return ramdisk_size(str);
}

static int __init ramdisk_blocksize(char *str)
{
	rd_blocksize = simple_strtol(str,NULL,0);
	return 1;
}

__setup("ramdisk_start=", ramdisk_start_setup);
__setup("load_ramdisk=", load_ramdisk);
__setup("prompt_ramdisk=", prompt_ramdisk);
__setup("ramdisk=", ramdisk_size);
__setup("ramdisk_size=", ramdisk_size2);
__setup("ramdisk_blocksize=", ramdisk_blocksize);

#endif

/*
 *  Basically, my strategy here is to set up a buffer-head which can't be
 *  deleted, and make that my Ramdisk.  If the request is outside of the
 *  allocated size, we must get rid of it...
 *
 * 19-JAN-1998  Richard Gooch <[e-mail]>  Added devfs support
 *
 */
static int rd_make_request(request_queue_t * q, int rw, struct buffer_head *sbh)
{
	unsigned int minor;
	unsigned long offset, len;
	struct buffer_head *rbh;
	char *bdata;

	
	minor = MINOR(sbh->b_rdev);

	if (minor >= NUM_RAMDISKS)
		goto fail;

	
	offset = sbh->b_rsector << 9;
	len = sbh->b_size;

	if ((offset + len) > rd_length[minor])
		goto fail;

	if (rw==READA)
		rw=READ;
	if ((rw != READ) && (rw != WRITE)) {
		printk(KERN_INFO "RAMDISK: bad command: %d\n", rw);
		goto fail;
	}

	rbh = getblk(sbh->b_rdev, sbh->b_rsector/(sbh->b_size>>9), sbh->b_size);
	/* I think that it is safe to assume that rbh is not in HighMem, though
	 * sbh might be - NeilBrown
	 */
	bdata = bh_kmap(sbh);
	if (rw == READ) {
		if (sbh != rbh)
			memcpy(bdata, rbh->b_data, rbh->b_size);
	} else
		if (sbh != rbh)
			memcpy(rbh->b_data, bdata, rbh->b_size);
	bh_kunmap(sbh);
	mark_buffer_protected(rbh);
	brelse(rbh);

	sbh->b_end_io(sbh,1);
	return 0;
 fail:
	sbh->b_end_io(sbh,0);
	return 0;
} 

static int rd_ioctl(struct inode *inode, struct file *file, unsigned int cmd, unsigned long arg)
{
	unsigned int minor;

	if (!inode || !inode->i_rdev) 	
		return -EINVAL;

	minor = MINOR(inode->i_rdev);

	switch (cmd) {
		case BLKFLSBUF:
			if (!capable(CAP_SYS_ADMIN))
				return -EACCES;
			/* special: we want to release the ramdisk memory,
			   it's not like with the other blockdevices where
			   this ioctl only flushes away the buffer cache. */
			if ((atomic_read(&inode->i_bdev->bd_openers) > 2))
				return -EBUSY;
			destroy_buffers(inode->i_rdev);
			rd_blocksizes[minor] = 0;
			break;

         	case BLKGETSIZE:   /* Return device size */
			if (!arg)  return -EINVAL;
			return put_user(rd_kbsize[minor] << 1, (long *) arg);

		case BLKROSET:
		case BLKROGET:
		case BLKSSZGET:
			return blk_ioctl(inode->i_rdev, cmd, arg);

		default:
			return -EINVAL;
	};

	return 0;
}


#ifdef CONFIG_BLK_DEV_INITRD

static ssize_t initrd_read(struct file *file, char *buf,
			   size_t count, loff_t *ppos)
{
	int left;

	left = initrd_end - initrd_start - *ppos;
	if (count > left) count = left;
	if (count == 0) return 0;
	copy_to_user(buf, (char *)initrd_start + *ppos, count);
	*ppos += count;
	return count;
}


static int initrd_release(struct inode *inode,struct file *file)
{
	extern void free_initrd_mem(unsigned long, unsigned long);

	lock_kernel();
	if (!--initrd_users) {
		blkdev_put(inode->i_bdev, BDEV_FILE);
		iput(inode);
		free_initrd_mem(initrd_start, initrd_end);
		initrd_start = 0;
	}
	unlock_kernel();
	return 0;
}


static struct file_operations initrd_fops = {
	read:		initrd_read,
	release:	initrd_release,
};

#endif


static int rd_open(struct inode * inode, struct file * filp)
{
#ifdef CONFIG_BLK_DEV_INITRD
	if (DEVICE_NR(inode->i_rdev) == INITRD_MINOR) {
		if (!initrd_start) return -ENODEV;
		initrd_users++;
		filp->f_op = &initrd_fops;
		return 0;
	}
#endif

	if (DEVICE_NR(inode->i_rdev) >= NUM_RAMDISKS)
		return -ENXIO;

	/*
	 * Immunize device against invalidate_buffers() and prune_icache().
	 */
	if (rd_inode[DEVICE_NR(inode->i_rdev)] == NULL) {
		if (!inode->i_bdev) return -ENXIO;
		if ((rd_inode[DEVICE_NR(inode->i_rdev)] = igrab(inode)) != NULL)
			atomic_inc(&rd_inode[DEVICE_NR(inode->i_rdev)]->i_bdev->bd_openers);
	}

	MOD_INC_USE_COUNT;

	return 0;
}

static int rd_release(struct inode * inode, struct file * filp)
{
	MOD_DEC_USE_COUNT;
	return 0;
}

static struct block_device_operations fd_fops = {
	open:		rd_open,
	release:	rd_release,
	ioctl:		rd_ioctl,
};

#ifdef MODULE
/* Before freeing the module, invalidate all of the protected buffers! */
static void __exit rd_cleanup (void)
{
	int i;

	for (i = 0 ; i < NUM_RAMDISKS; i++) {
		if (rd_inode[i]) {
			/* withdraw invalidate_buffers() and prune_icache() immunity */
			atomic_dec(&rd_inode[i]->i_bdev->bd_openers);
			/* remove stale pointer to module address space */
			rd_inode[i]->i_bdev->bd_op = NULL;
			iput(rd_inode[i]);
		}
		destroy_buffers(MKDEV(MAJOR_NR, i));
	}

	devfs_unregister (devfs_handle);
	unregister_blkdev( MAJOR_NR, "ramdisk" );
	hardsect_size[MAJOR_NR] = NULL;
	blksize_size[MAJOR_NR] = NULL;
	blk_size[MAJOR_NR] = NULL;
}
#endif

/* This is the registration and initialization section of the RAM disk driver */
int __init rd_init (void)
{
	int		i;

	if (rd_blocksize > PAGE_SIZE || rd_blocksize < 512 ||
	    (rd_blocksize & (rd_blocksize-1)))
	{
		printk("RAMDISK: wrong blocksize %d, reverting to defaults\n",
		       rd_blocksize);
		rd_blocksize = BLOCK_SIZE;
	}

	if (register_blkdev(MAJOR_NR, "ramdisk", &fd_fops)) {
		printk("RAMDISK: Could not get major %d", MAJOR_NR);
		return -EIO;
	}

	blk_queue_make_request(BLK_DEFAULT_QUEUE(MAJOR_NR), &rd_make_request);

	for (i = 0; i < NUM_RAMDISKS; i++) {
		/* rd_size is given in kB */
		rd_length[i] = rd_size << 10;
		rd_hardsec[i] = rd_blocksize;
		rd_blocksizes[i] = rd_blocksize;
		rd_kbsize[i] = rd_size;
	}
	devfs_handle = devfs_mk_dir (NULL, "rd", NULL);
	devfs_register_series (devfs_handle, "%u", NUM_RAMDISKS,
			       DEVFS_FL_DEFAULT, MAJOR_NR, 0,
			       S_IFBLK | S_IRUSR | S_IWUSR,
			       &fd_fops, NULL);

	for (i = 0; i < NUM_RAMDISKS; i++)
		register_disk(NULL, MKDEV(MAJOR_NR,i), 1, &fd_fops, rd_size<<1);

#ifdef CONFIG_BLK_DEV_INITRD
	/* We ought to separate initrd operations here */
	register_disk(NULL, MKDEV(MAJOR_NR,INITRD_MINOR), 1, &fd_fops, rd_size<<1);
#endif

	hardsect_size[MAJOR_NR] = rd_hardsec;		/* Size of the RAM disk blocks */
	blksize_size[MAJOR_NR] = rd_blocksizes;		/* Avoid set_blocksize() check */
	blk_size[MAJOR_NR] = rd_kbsize;			/* Size of the RAM disk in kB  */

		/* rd_size is given in kB */
	printk("RAMDISK driver initialized: "
	       "%d RAM disks of %dK size %d blocksize\n",
	       NUM_RAMDISKS, rd_size, rd_blocksize);

	return 0;
}

#ifdef MODULE
module_init(rd_init);
module_exit(rd_cleanup);
#endif

/* loadable module support */
MODULE_PARM     (rd_size, "1i");
MODULE_PARM_DESC(rd_size, "Size of each RAM disk in kbytes.");
MODULE_PARM     (rd_blocksize, "i");
MODULE_PARM_DESC(rd_blocksize, "Blocksize of each RAM disk in bytes.");

/* End of non-loading portions of the RAM disk driver */