This patch enables the cram filesystem to be used as an initrd. Note that you
have to set ramdisk_blocksize=4096.

diff -rNu ../linux-2.4.0/drivers/block/rd.c ./drivers/block/rd.c
--- ../linux-2.4.0/drivers/block/rd.c	Mon Dec 18 20:57:17 2000
+++ ./drivers/block/rd.c	Tue Jan  9 01:24:36 2001
@@ -47,6 +47,7 @@
 #include <linux/minix_fs.h>
 #include <linux/ext2_fs.h>
 #include <linux/romfs_fs.h>
+#include <linux/cramfs_fs.h>
 #include <linux/fs.h>
 #include <linux/kernel.h>
 #include <linux/hdreg.h>
@@ -473,6 +474,7 @@
 	struct minix_super_block *minixsb;
 	struct ext2_super_block *ext2sb;
 	struct romfs_super_block *romfsb;
+	struct cramfs_super *cramfsb;
 	int nblocks = -1;
 	unsigned char *buf;
 
@@ -483,6 +485,7 @@
 	minixsb = (struct minix_super_block *) buf;
 	ext2sb = (struct ext2_super_block *) buf;
 	romfsb = (struct romfs_super_block *) buf;
+	cramfsb = (struct cramfs_super *) buf;
 	memset(buf, 0xe5, size);
 
 	/*
@@ -512,6 +515,15 @@
 		       "RAMDISK: romfs filesystem found at block %d\n",
 		       start_block);
 		nblocks = (ntohl(romfsb->size)+BLOCK_SIZE-1)>>BLOCK_SIZE_BITS;
+		goto done;
+	}
+
+	/* so is cramfs */
+	if (cramfsb->magic == CRAMFS_MAGIC) {
+		printk(KERN_NOTICE
+		       "RAMDISK: cramfs filesystem found at block %d\n",
+		       start_block);
+		nblocks = (cramfsb->size+BLOCK_SIZE-1)>>BLOCK_SIZE_BITS;
 		goto done;
 	}
 
diff -rNu ../linux-2.4.0/fs/cramfs/README ./fs/cramfs/README
--- ../linux-2.4.0/fs/cramfs/README	Sun Jan 23 18:54:59 2000
+++ ./fs/cramfs/README	Tue Jan  9 01:24:36 2001
@@ -14,7 +14,7 @@
 	<directory_structure>
 	<data>
 
-<superblock>: struct cramfs_super (see cramfs.h).
+<superblock>: struct cramfs_super (see cramfs_fs.h).
 
 <directory_structure>:
 	For each file:
diff -rNu ../linux-2.4.0/fs/cramfs/cramfs.h ./fs/cramfs/cramfs.h
--- ../linux-2.4.0/fs/cramfs/cramfs.h	Sun Jan 23 18:54:59 2000
+++ ./fs/cramfs/cramfs.h	Thu Jan  1 01:00:00 1970
@@ -1,52 +0,0 @@
-#ifndef __CRAMFS_H
-#define __CRAMFS_H
-
-#define CRAMFS_MAGIC		0x28cd3d45	/* some random number */
-#define CRAMFS_SIGNATURE	"Compressed ROMFS"
-
-/*
- * Reasonably terse representation of the inode data.
- */
-struct cramfs_inode {
-	u32 mode:16, uid:16;
-	/* SIZE for device files is i_rdev */
-	u32 size:24, gid:8;
-	/* NAMELEN is the length of the file name, divided by 4 and
-           rounded up.  (cramfs doesn't support hard links.) */
-	/* OFFSET: For symlinks and non-empty regular files, this
-	   contains the offset (divided by 4) of the file data in
-	   compressed form (starting with an array of block pointers;
-	   see README).  For non-empty directories it is the offset
-	   (divided by 4) of the inode of the first file in that
-	   directory.  For anything else, offset is zero. */
-	u32 namelen:6, offset:26;
-};
-
-/*
- * Superblock information at the beginning of the FS.
- */
-struct cramfs_super {
-	u32 magic;		/* 0x28cd3d45 - random number */
-	u32 size;		/* Not used.  mkcramfs currently
-                                   writes a constant 1<<16 here. */
-	u32 flags;		/* 0 */
-	u32 future;		/* 0 */
-	u8 signature[16];	/* "Compressed ROMFS" */
-	u8 fsid[16];		/* random number */
-	u8 name[16];		/* user-defined name */
-	struct cramfs_inode root;	/* Root inode data */
-};
-
-/*
- * Valid values in super.flags.  Currently we refuse to mount
- * if (flags & ~CRAMFS_SUPPORTED_FLAGS).  Maybe that should be
- * changed to test super.future instead.
- */
-#define CRAMFS_SUPPORTED_FLAGS (0xff)
-
-/* Uncompression interfaces to the underlying zlib */
-int cramfs_uncompress_block(void *dst, int dstlen, void *src, int srclen);
-int cramfs_uncompress_init(void);
-int cramfs_uncompress_exit(void);
-
-#endif
diff -rNu ../linux-2.4.0/fs/cramfs/inode.c ./fs/cramfs/inode.c
--- ../linux-2.4.0/fs/cramfs/inode.c	Fri Jan  5 13:56:45 2001
+++ ./fs/cramfs/inode.c	Tue Jan  9 01:25:57 2001
@@ -20,7 +20,7 @@
 
 #include <asm/uaccess.h>
 
-#include "cramfs.h"
+#include <linux/cramfs_fs.h>
 
 static struct super_operations cramfs_ops;
 static struct inode_operations cramfs_dir_inode_operations;
@@ -138,7 +138,7 @@
 		struct buffer_head * bh = bh_array[i];
 		if (bh) {
 			memcpy(data, bh->b_data, PAGE_CACHE_SIZE);
-			bforget(bh);
+			brelse(bh);
 		} else
 			memset(data, 0, PAGE_CACHE_SIZE);
 		data += PAGE_CACHE_SIZE;
diff -rNu ../linux-2.4.0/include/linux/cramfs_fs.h ./include/linux/cramfs_fs.h
--- ../linux-2.4.0/include/linux/cramfs_fs.h	Thu Jan  1 01:00:00 1970
+++ ./include/linux/cramfs_fs.h	Tue Jan  9 01:27:15 2001
@@ -0,0 +1,51 @@
+#ifndef __CRAMFS_H
+#define __CRAMFS_H
+
+#define CRAMFS_MAGIC		0x28cd3d45	/* some random number */
+#define CRAMFS_SIGNATURE	"Compressed ROMFS"
+
+/*
+ * Reasonably terse representation of the inode data.
+ */
+struct cramfs_inode {
+	u32 mode:16, uid:16;
+	/* SIZE for device files is i_rdev */
+	u32 size:24, gid:8;
+	/* NAMELEN is the length of the file name, divided by 4 and
+           rounded up.  (cramfs doesn't support hard links.) */
+	/* OFFSET: For symlinks and non-empty regular files, this
+	   contains the offset (divided by 4) of the file data in
+	   compressed form (starting with an array of block pointers;
+	   see README).  For non-empty directories it is the offset
+	   (divided by 4) of the inode of the first file in that
+	   directory.  For anything else, offset is zero. */
+	u32 namelen:6, offset:26;
+};
+
+/*
+ * Superblock information at the beginning of the FS.
+ */
+struct cramfs_super {
+	u32 magic;		/* 0x28cd3d45 - random number */
+	u32 size;		/* Size of fs in bytes */
+	u32 flags;		/* 0 */
+	u32 future;		/* 0 */
+	u8 signature[16];	/* "Compressed ROMFS" */
+	u8 fsid[16];		/* random number */
+	u8 name[16];		/* user-defined name */
+	struct cramfs_inode root;	/* Root inode data */
+};
+
+/*
+ * Valid values in super.flags.  Currently we refuse to mount
+ * if (flags & ~CRAMFS_SUPPORTED_FLAGS).  Maybe that should be
+ * changed to test super.future instead.
+ */
+#define CRAMFS_SUPPORTED_FLAGS (0xff)
+
+/* Uncompression interfaces to the underlying zlib */
+int cramfs_uncompress_block(void *dst, int dstlen, void *src, int srclen);
+int cramfs_uncompress_init(void);
+int cramfs_uncompress_exit(void);
+
+#endif
diff -rNu ../linux-2.4.0/scripts/cramfs/mkcramfs.c ./scripts/cramfs/mkcramfs.c
--- ../linux-2.4.0/scripts/cramfs/mkcramfs.c	Mon Dec 18 20:54:27 2000
+++ ./scripts/cramfs/mkcramfs.c	Tue Jan  9 01:24:36 2001
@@ -17,7 +17,7 @@
 typedef unsigned short u16;
 typedef unsigned int u32;
 
-#include "cramfs.h"
+#include <linux/cramfs_fs.h>
 
 static const char *progname = "mkcramfs";
 
@@ -274,16 +274,20 @@
 }
 
 /* Returns sizeof(struct cramfs_super), which includes the root inode. */
-static unsigned int write_superblock(struct entry *root, char *base)
+static unsigned int get_superblock_size(struct entry *root, char *base)
+{
+	return sizeof(struct cramfs_super);
+}
+
+/* Returns sizeof(struct cramfs_super), which includes the root inode. */
+static unsigned int write_superblock(struct entry *root, char *base, unsigned int size)
 {
 	struct cramfs_super *super = (struct cramfs_super *) base;
 	unsigned int offset = sizeof(struct cramfs_super);
 
 	super->magic = CRAMFS_MAGIC;
 	super->flags = 0;
-	/* Note: 0x10000 is meaningless, which is a bug; but
-	   super->size is never used anyway. */
-	super->size = 0x10000;
+	super->size = size;
 	memcpy(super->signature, CRAMFS_SIGNATURE, sizeof(super->signature));
 	set_random(super->fsid, sizeof(super->fsid));
 	strncpy(super->name, "Compressed", sizeof(super->name));
@@ -521,6 +525,7 @@
 	struct entry *root_entry;
 	char *rom_image;
 	unsigned int offset;
+	unsigned int sbsize;
 	ssize_t written;
 	int fd;
 	loff_t fslen_ub = 0; /* initial guess (upper-bound) of
@@ -575,10 +580,9 @@
 		perror("ROM image map");
 		exit(1);
 	}
-	offset = write_superblock(root_entry, rom_image);
-	printf("Super block: %d bytes\n", offset);
 
-	offset = write_directory_structure(root_entry->child, rom_image, offset);
+	sbsize = get_superblock_size(root_entry, rom_image);
+	offset = write_directory_structure(root_entry->child, rom_image, sbsize);
 	printf("Directory data: %d bytes\n", offset);
 
 	offset = write_data(root_entry, rom_image, offset);
@@ -586,6 +590,11 @@
 	/* We always write a multiple of blksize bytes, so that
            losetup works. */
 	offset = ((offset - 1) | (blksize - 1)) + 1;
+
+	/* Finally, write the superblock, with the given size */
+	write_superblock(root_entry, rom_image, offset);
+	printf("Super block: %d bytes\n", sbsize);
+
 	printf("Everything: %d kilobytes\n", offset >> 10);
 
 	written = write(fd, rom_image, offset);