rd.c

讲述linux的初始化过程

#ifdef RD_LOADER 
/*
 * This routine tries to find a RAM disk image to load, and returns the
 * number of blocks to read for a non-compressed image, 0 if the image
 * is a compressed image, and -1 if an image with the right magic
 * numbers could not be found.
 *
 * We currently check for the following magic numbers:
 * 	minix
 * 	ext2
 *	romfs
 * 	gzip
 */
int __init 
identify_ramdisk_image(kdev_t device, struct file *fp, int start_block)
{
	const int size = 512;
	struct minix_super_block *minixsb;
	struct ext2_super_block *ext2sb;
	struct romfs_super_block *romfsb;
	int nblocks = -1;
	unsigned char *buf;

	buf = kmalloc(size, GFP_KERNEL);
	if (buf == 0)
		return -1;

	minixsb = (struct minix_super_block *) buf;
	ext2sb = (struct ext2_super_block *) buf;
	romfsb = (struct romfs_super_block *) buf;
	memset(buf, 0xe5, size);

	/*
	 * Read block 0 to test for gzipped kernel
	 */
	if (fp->f_op->llseek)
		fp->f_op->llseek(fp, start_block * BLOCK_SIZE, 0);
	fp->f_pos = start_block * BLOCK_SIZE;
	
	fp->f_op->read(fp, buf, size, &fp->f_pos);

	/*
	 * If it matches the gzip magic numbers, return -1
	 */
	if (buf[0] == 037 && ((buf[1] == 0213) || (buf[1] == 0236))) {
		printk(KERN_NOTICE
		       "RAMDISK: Compressed image found at block %d\n",
		       start_block);
		nblocks = 0;
		goto done;
	}

	/* romfs is at block zero too */
	if (romfsb->word0 == ROMSB_WORD0 &&
	    romfsb->word1 == ROMSB_WORD1) {
		printk(KERN_NOTICE
		       "RAMDISK: romfs filesystem found at block %d\n",
		       start_block);
		nblocks = (ntohl(romfsb->size)+BLOCK_SIZE-1)>>BLOCK_SIZE_BITS;
		goto done;
	}

	/*
	 * Read block 1 to test for minix and ext2 superblock
	 */
	if (fp->f_op->llseek)
		fp->f_op->llseek(fp, (start_block+1) * BLOCK_SIZE, 0);
	fp->f_pos = (start_block+1) * BLOCK_SIZE;

	fp->f_op->read(fp, buf, size, &fp->f_pos);
		
	/* Try minix */
	if (minixsb->s_magic == MINIX_SUPER_MAGIC ||
	    minixsb->s_magic == MINIX_SUPER_MAGIC2) {
		printk(KERN_NOTICE
		       "RAMDISK: Minix filesystem found at block %d\n",
		       start_block);
		nblocks = minixsb->s_nzones << minixsb->s_log_zone_size;
		goto done;
	}

	/* Try ext2 */
	if (ext2sb->s_magic == cpu_to_le16(EXT2_SUPER_MAGIC)) {
		printk(KERN_NOTICE
		       "RAMDISK: ext2 filesystem found at block %d\n",
		       start_block);
		nblocks = le32_to_cpu(ext2sb->s_blocks_count);
		goto done;
	}

	printk(KERN_NOTICE
	       "RAMDISK: Couldn't find valid RAM disk image starting at %d.\n",
	       start_block);
	
done:
	if (fp->f_op->llseek)
		fp->f_op->llseek(fp, start_block * BLOCK_SIZE, 0);
	fp->f_pos = start_block * BLOCK_SIZE;	

	kfree(buf);
	return nblocks;
}

/*
 * This routine loads in the RAM disk image.
 */
static void __init rd_load_image(kdev_t device, int offset, int unit)
{
 	struct inode *inode, *out_inode;
	struct file infile, outfile;
	struct dentry in_dentry, out_dentry;
	mm_segment_t fs;
	kdev_t ram_device;
	int nblocks, i;
	char *buf;
	unsigned short rotate = 0;
	unsigned short devblocks = 0;
	char rotator[4] = { '|' , '/' , '-' , '\\' };

	ram_device = MKDEV(MAJOR_NR, unit);

	if ((inode = get_empty_inode()) == NULL)
		return;
	memset(&infile, 0, sizeof(infile));
	memset(&in_dentry, 0, sizeof(in_dentry));
	infile.f_mode = 1; /* read only */
	infile.f_dentry = &in_dentry;
	in_dentry.d_inode = inode;
	infile.f_op = &def_blk_fops;
	init_special_inode(inode, S_IFBLK | S_IRUSR, kdev_t_to_nr(device));

	if ((out_inode = get_empty_inode()) == NULL)
		goto free_inode;
	memset(&outfile, 0, sizeof(outfile));
	memset(&out_dentry, 0, sizeof(out_dentry));
	outfile.f_mode = 3; /* read/write */
	outfile.f_dentry = &out_dentry;
	out_dentry.d_inode = out_inode;
	outfile.f_op = &def_blk_fops;
	init_special_inode(out_inode, S_IFBLK | S_IRUSR | S_IWUSR, kdev_t_to_nr(ram_device));

	if (blkdev_open(inode, &infile) != 0)
		goto free_inode;
	if (blkdev_open(out_inode, &outfile) != 0)
		goto free_inodes;

	fs = get_fs();
	set_fs(KERNEL_DS);
	
	nblocks = identify_ramdisk_image(device, &infile, offset);
	if (nblocks < 0)
		goto done;

	if (nblocks == 0) {
#ifdef BUILD_CRAMDISK
		if (crd_load(&infile, &outfile) == 0)
			goto successful_load;
#else
		printk(KERN_NOTICE
		       "RAMDISK: Kernel does not support compressed "
		       "RAM disk images\n");
#endif
		goto done;
	}

	/*
	 * NOTE NOTE: nblocks suppose that the blocksize is BLOCK_SIZE, so
	 * rd_load_image will work only with filesystem BLOCK_SIZE wide!
	 * So make sure to use 1k blocksize while generating ext2fs
	 * ramdisk-images.
	 */
	if (nblocks > (rd_length[unit] >> BLOCK_SIZE_BITS)) {
		printk("RAMDISK: image too big! (%d/%ld blocks)\n",
		       nblocks, rd_length[unit] >> BLOCK_SIZE_BITS);
		goto done;
	}
		
	/*
	 * OK, time to copy in the data
	 */
	buf = kmalloc(BLOCK_SIZE, GFP_KERNEL);
	if (buf == 0) {
		printk(KERN_ERR "RAMDISK: could not allocate buffer\n");
		goto done;
	}

	if (blk_size[MAJOR(device)])
		devblocks = blk_size[MAJOR(device)][MINOR(device)];

#ifdef CONFIG_BLK_DEV_INITRD
	if (MAJOR(device) == MAJOR_NR && MINOR(device) == INITRD_MINOR)
		devblocks = nblocks;
#endif

	if (devblocks == 0) {
		printk(KERN_ERR "RAMDISK: could not determine device size\n");
		goto done;
	}

	printk(KERN_NOTICE "RAMDISK: Loading %d blocks [%d disk%s] into ram disk... ", 
		nblocks, ((nblocks-1)/devblocks)+1, nblocks>devblocks ? "s" : "");
	for (i=0; i < nblocks; i++) {
		if (i && (i % devblocks == 0)) {
			printk("done disk #%d.\n", i/devblocks);
			rotate = 0;
			invalidate_buffers(device);
			if (infile.f_op->release)
				infile.f_op->release(inode, &infile);
			printk("Please insert disk #%d and press ENTER\n", i/devblocks+1);
			wait_for_keypress();
			if (blkdev_open(inode, &infile) != 0)  {
				printk("Error opening disk.\n");
				goto done;
			}
			infile.f_pos = 0;
			printk("Loading disk #%d... ", i/devblocks+1);
		}
		infile.f_op->read(&infile, buf, BLOCK_SIZE, &infile.f_pos);
		outfile.f_op->write(&outfile, buf, BLOCK_SIZE, &outfile.f_pos);
#if !defined(CONFIG_ARCH_S390)
		if (!(i % 16)) {
			printk("%c\b", rotator[rotate & 0x3]);
			rotate++;
		}
#endif
	}
	printk("done.\n");
	kfree(buf);

successful_load:
	invalidate_buffers(device);
	ROOT_DEV = MKDEV(MAJOR_NR, unit);
	if (ROOT_DEVICE_NAME != NULL) strcpy (ROOT_DEVICE_NAME, "rd/0");

done:
	if (infile.f_op->release)
		infile.f_op->release(inode, &infile);
	set_fs(fs);
	return;
free_inodes: /* free inodes on error */ 
	iput(out_inode);
	blkdev_put(inode->i_bdev, BDEV_FILE);
free_inode:
	iput(inode);
}

#ifdef CONFIG_MAC_FLOPPY
int swim3_fd_eject(int devnum);
#endif

static void __init rd_load_disk(int n)
{
#ifdef CONFIG_BLK_DEV_INITRD
	extern kdev_t real_root_dev;
#endif

	if (rd_doload == 0)
		return;

	if (MAJOR(ROOT_DEV) != FLOPPY_MAJOR
#ifdef CONFIG_BLK_DEV_INITRD
		&& MAJOR(real_root_dev) != FLOPPY_MAJOR
#endif
	)
		return;

	if (rd_prompt) {
#ifdef CONFIG_BLK_DEV_FD
		floppy_eject();
#endif
#ifdef CONFIG_MAC_FLOPPY
		if(MAJOR(ROOT_DEV) == FLOPPY_MAJOR)
			swim3_fd_eject(MINOR(ROOT_DEV));
		else if(MAJOR(real_root_dev) == FLOPPY_MAJOR)
			swim3_fd_eject(MINOR(real_root_dev));
#endif
		printk(KERN_NOTICE
		       "VFS: Insert root floppy disk to be loaded into RAM disk and press ENTER\n");
		wait_for_keypress();
	}

	rd_load_image(ROOT_DEV,rd_image_start, n);

}

void __init rd_load(void)
{
	rd_load_disk(0);
}

void __init rd_load_secondary(void)
{
	rd_load_disk(1);
}

#ifdef CONFIG_BLK_DEV_INITRD
void __init initrd_load(void)
{
	rd_load_image(MKDEV(MAJOR_NR, INITRD_MINOR),rd_image_start,0);
}
#endif

#endif /* RD_LOADER */

#ifdef BUILD_CRAMDISK

/*
 * gzip declarations
 */

#define OF(args)  args

#ifndef memzero
#define memzero(s, n)     memset ((s), 0, (n))
#endif

typedef unsigned char  uch;
typedef unsigned short ush;
typedef unsigned long  ulg;

#define INBUFSIZ 4096
#define WSIZE 0x8000    /* window size--must be a power of two, and */
			/*  at least 32K for zip's deflate method */

static uch *inbuf;
static uch *window;

static unsigned insize;  /* valid bytes in inbuf */
static unsigned inptr;   /* index of next byte to be processed in inbuf */
static unsigned outcnt;  /* bytes in output buffer */
static int exit_code;
static long bytes_out;
static struct file *crd_infp, *crd_outfp;

#define get_byte()  (inptr < insize ? inbuf[inptr++] : fill_inbuf())
		
/* Diagnostic functions (stubbed out) */
#define Assert(cond,msg)
#define Trace(x)
#define Tracev(x)
#define Tracevv(x)
#define Tracec(c,x)
#define Tracecv(c,x)

#define STATIC static

static int  fill_inbuf(void);
static void flush_window(void);
static void *malloc(int size);
static void free(void *where);
static void error(char *m);
static void gzip_mark(void **);
static void gzip_release(void **);

#include "../../lib/inflate.c"

static void __init *malloc(int size)
{
	return kmalloc(size, GFP_KERNEL);
}

static void __init free(void *where)
{
	kfree(where);
}

static void __init gzip_mark(void **ptr)
{
}

static void __init gzip_release(void **ptr)
{
}


/* ===========================================================================
 * Fill the input buffer. This is called only when the buffer is empty
 * and at least one byte is really needed.
 */
static int __init fill_inbuf(void)
{
	if (exit_code) return -1;
	
	insize = crd_infp->f_op->read(crd_infp, inbuf, INBUFSIZ,
				      &crd_infp->f_pos);
	if (insize == 0) return -1;

	inptr = 1;

	return inbuf[0];
}

/* ===========================================================================
 * Write the output window window[0..outcnt-1] and update crc and bytes_out.
 * (Used for the decompressed data only.)
 */
static void __init flush_window(void)
{
    ulg c = crc;         /* temporary variable */
    unsigned n;
    uch *in, ch;
    
    crd_outfp->f_op->write(crd_outfp, window, outcnt, &crd_outfp->f_pos);
    in = window;
    for (n = 0; n < outcnt; n++) {
	    ch = *in++;
	    c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
    }
    crc = c;
    bytes_out += (ulg)outcnt;
    outcnt = 0;
}

static void __init error(char *x)
{
	printk(KERN_ERR "%s", x);
	exit_code = 1;
}

static int __init 
crd_load(struct file * fp, struct file *outfp)
{
	int result;

	insize = 0;		/* valid bytes in inbuf */
	inptr = 0;		/* index of next byte to be processed in inbuf */
	outcnt = 0;		/* bytes in output buffer */
	exit_code = 0;
	bytes_out = 0;
	crc = (ulg)0xffffffffL; /* shift register contents */

	crd_infp = fp;
	crd_outfp = outfp;
	inbuf = kmalloc(INBUFSIZ, GFP_KERNEL);
	if (inbuf == 0) {
		printk(KERN_ERR "RAMDISK: Couldn't allocate gzip buffer\n");
		return -1;
	}
	window = kmalloc(WSIZE, GFP_KERNEL);
	if (window == 0) {
		printk(KERN_ERR "RAMDISK: Couldn't allocate gzip window\n");
		kfree(inbuf);
		return -1;
	}
	makecrc();
	result = gunzip();
	kfree(inbuf);
	kfree(window);
	return result;
}

#endif  /* BUILD_CRAMDISK */