Add support for memory disk (md). The size of the memory disk

is determined by MD_IMAGE_SIZE. A file system can be embedded
into the loader with /sys/tools/embed_mfs.sh.
Note that md.c is not included when MD_IMAGE_SIZE is not set.

sys/boot/common/Makefile.inc

@@ -23,6 +23,11 @@ SRCS+=	dev_net.c
 SRCS+=  bcache.c
 .endif
 
+.if defined(MD_IMAGE_SIZE)
+CFLAGS+= -DMD_IMAGE_SIZE=${MD_IMAGE_SIZE}
+SRCS+=	md.c
+.endif
+
 # Machine-independant ISA PnP
 .if defined(HAVE_ISABUS)
 SRCS+=	isapnp.c

sys/boot/common/md.c

@@ -0,0 +1,151 @@
+/*-
+ * Copyright (c) 2009 Marcel Moolenaar
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <sys/param.h>
+#include <sys/endian.h>
+#include <sys/queue.h>
+#include <machine/stdarg.h>
+#include <stand.h>
+
+#include "bootstrap.h"
+
+#define	MD_BLOCK_SIZE	512
+
+#ifndef MD_IMAGE_SIZE
+#error Must be compiled with MD_IMAGE_SIZE defined
+#endif
+#if (MD_IMAGE_SIZE == 0 || MD_IMAGE_SIZE % MD_BLOCK_SIZE)
+#error Image size must be a multiple of 512.
+#endif
+
+/*
+ * Preloaded image gets put here.
+ * Applications that patch the object with the image can determine
+ * the size looking at the start and end markers (strings),
+ * so we want them contiguous.
+ */
+static struct {
+	u_char start[MD_IMAGE_SIZE];
+	u_char end[128];
+} md_image = {
+	.start = "MFS Filesystem goes here",
+	.end = "MFS Filesystem had better STOP here",
+};
+
+/* devsw I/F */
+static int md_init(void);
+static int md_strategy(void *, int, daddr_t, size_t, char *, size_t *);
+static int md_open(struct open_file *, ...);
+static int md_close(struct open_file *);
+static void md_print(int);
+
+struct devsw md_dev = {
+	"md",
+	DEVT_DISK,
+	md_init,
+	md_strategy,
+	md_open,
+	md_close,
+	noioctl,
+	md_print
+};
+
+static int
+md_init(void)
+{
+
+	return (0);
+}
+
+static int
+md_strategy(void *devdata, int rw, daddr_t blk, size_t size, char *buf,
+    size_t *rsize)
+{
+	struct devdesc *dev = (struct devdesc *)devdata;
+	size_t ofs;
+
+	if (dev->d_unit != 0)
+		return (ENXIO);
+
+	if (blk < 0 || blk >= (MD_IMAGE_SIZE / MD_BLOCK_SIZE))
+		return (EIO);
+
+	if (size % MD_BLOCK_SIZE)
+		return (EIO);
+
+	ofs = blk * MD_BLOCK_SIZE;
+	if ((ofs + size) > MD_IMAGE_SIZE)
+		size = MD_IMAGE_SIZE - ofs;
+
+	if (rsize != 0)
+		*rsize = size;
+
+	switch (rw) {
+	case F_READ:
+		bcopy(md_image.start + ofs, buf, size);
+		return (0);
+	case F_WRITE:
+		bcopy(buf, md_image.start + ofs, size);
+		return (0);
+	}
+
+	return (ENODEV);
+}
+
+static int
+md_open(struct open_file *f, ...)
+{
+	va_list ap;
+	struct devdesc *dev;
+
+	va_start(ap, f);
+	dev = va_arg(ap, struct devdesc *);
+	va_end(ap);
+
+	if (dev->d_unit != 0)
+		return (ENXIO);
+
+	return (0);
+}
+
+static int
+md_close(struct open_file *f)
+{
+	struct devdesc *dev;
+
+	dev = (struct devdesc *)(f->f_devdata);
+	return ((dev->d_unit != 0) ? ENXIO : 0);
+}
+
+static void
+md_print(int verbose)
+{
+
+	printf("MD (%u bytes)\n", MD_IMAGE_SIZE);
+}