Fix MFS builds when both MD_ROOT_SIZE and MFS_IMAGE are specified

MD_ROOT_SIZE and embed_mfs.sh were basically retired as part of
https://reviews.freebsd.org/D2903 .
However, when building a kernel with 'options MD_ROOT_SIZE' specified, this
results in a non-working MFS, as within sys/dev/md/md.c we fall within the
wrong # ifdef.

This patch implements the following:

* Allow kernels to be built without the MD_ROOT_SIZE option, which results
  in a kernel built as per D2903.
* Allow kernels to be built with the MD_ROOT_SIZE option, which results
  in a kernel built similarly to the pre-D2903 way, with the following
  differences:
  * The MFS is now put in a separate section within the kernel (oldmfs,
    so it differs from the mfs section introduced by D2903).
  * embed_mfs.sh is changed, so it looks up the oldmfs section within the
    kernel, gets its size and offset, sees if the MFS will fit within the
    allocated oldmfs section and only if all is well does a dd of the MFS
    image into the kernel.

Submitted by:	Stanislav Galabov <sgalabov@gmail.com>
Reviewed by:	brooks, imp
Differential Revision:	https://reviews.freebsd.org/D5093

1 files changed, 16 insertions, 4 deletions

diff --git a/sys/tools/embed_mfs.sh b/sys/tools/embed_mfs.sh
index 785cf3f..3f20257 100644
--- a/sys/tools/embed_mfs.sh
+++ b/sys/tools/embed_mfs.sh
@@ -32,8 +32,20 @@
 # $2: MFS image filename
 #
 
-obs=`strings -at d $1 | grep "MFS Filesystem goes here" | awk '{print $1}'`
-dd if=$2 ibs=8192 of=$1 obs=${obs} oseek=1 conv=notrunc 2> /dev/null
+mfs_size=`stat -f '%z' $2 2> /dev/null`
+# If we can't determine MFS image size - bail.
+[ -z ${mfs_size} ] && echo "Can't determine MFS image size" && exit 1
 
-strings $1 | grep 'MFS Filesystem had better STOP here' > /dev/null || \
-	(rm $1 && echo "MFS image too large" && false)
+sec_info=`objdump -h $1 2> /dev/null | grep " oldmfs "`
+# If we can't find the mfs section within the given kernel - bail.
+[ -z "${sec_info}" ] && echo "Can't locate mfs section within kernel" && exit 1
+
+sec_size=`echo ${sec_info} | awk '{printf("%d", "0x" $3)}' 2> /dev/null`
+sec_start=`echo ${sec_info} | awk '{printf("%d", "0x" $6)}' 2> /dev/null`
+
+# If the mfs section size is smaller than the mfs image - bail.
+[ ${sec_size} -lt ${mfs_size} ] && echo "MFS image too large" && exit 1
+
+# Dump the mfs image into the mfs section
+dd if=$2 ibs=8192 of=$1 obs=${sec_start} oseek=1 conv=notrunc 2> /dev/null && \
+    echo "MFS image embedded into kernel" && exit 0