loopback-file-system-support.patch

https://bugs.debian.org/cgi-bin/bugreport.cgi?att=0;bug=468114;msg=32

On 2015-08-11, Vagrant Cascadian wrote:
> On 2015-08-11, Vagrant Cascadian wrote:
>> I've taken a quick stab as refreshing this, though I haven't yet tested
>> it. I did move mounting of the loopback to mount_loop_root in functions,
>> as I would like to eventually support loopback mounted files from NFS.
>
> Made some small changes, updated and *tested* this time! Patch below...

And added NFS support! Full patch below...

live well,
  vagrant

---
 init              | 12 ++++++++++++
 initramfs-tools.7 | 13 +++++++++++++
 scripts/functions | 40 ++++++++++++++++++++++++++++++++++++++++
 scripts/local     |  7 ++++++-
 scripts/nfs       |  4 ++++
 5 files changed, 75 insertions(+), 1 deletion(-)

diff --git a/init b/init
index 3dc9f6b..fe1005a 100755
--- a/init
+++ b/init
@@ -49,6 +49,9 @@ export ROOT=
 export ROOTDELAY=
 export ROOTFLAGS=
 export ROOTFSTYPE=
+export LOOP=
+export LOOPFLAGS=
+export LOOPFSTYPE=
 export IP=
 export DEVICE=
 export BOOT=
@@ -104,6 +107,15 @@ for x in $(cat /proc/cmdline); do
 			;;
 		esac
 		;;
+	loop=*)
+		LOOP="${x#loop=}"
+		;;
+	loopflags=*)
+		LOOPFLAGS="-o ${x#loopflags=}"
+		;;
+	loopfstype=*)
+		LOOPFSTYPE="${x#loopfstype=}"
+		;;
 	nfsroot=*)
 		# shellcheck disable=SC2034
 		NFSROOT="${x#nfsroot=}"
diff --git a/initramfs-tools.7 b/initramfs-tools.7
index 45b7de7..745e7a0 100644
--- a/initramfs-tools.7
+++ b/initramfs-tools.7
@@ -53,6 +53,19 @@ The default is 180 seconds.
 \fB\fI rootflags
 set the file system mount option string.
 
+.TP
+\fB\fI loop
+path within the original root file system to loop-mount and use as the
+real root file system.
+
+.TP
+\fB\fI loopflags
+set the loop file system mount option string, if applicable.
+
+.TP
+\fB\fI loopfstype
+set the loop file system type, if applicable.
+
 .TP
 \fB\fI nfsroot
 can be either "auto" to try to get the relevant information from DHCP or a
diff --git a/scripts/functions b/scripts/functions
index 077697f..a17e740 100644
--- a/scripts/functions
+++ b/scripts/functions
@@ -445,6 +445,46 @@ mountfs()
 	${type}_mount_fs "$1"
 }
 
+# Mount a loopback device, which is present on the mounted filesystem.
+mount_loop_root()
+{
+	mkdir -p /host
+	mount -o move "${rootmnt}" /host
+	loopfile="/host/${LOOP#/}"
+
+	while [ ! -e "$loopfile" ]; do
+		panic "ALERT! $loopfile does not exist.  Dropping to a shell!"
+	done
+
+	if [ "${readonly?}" = "y" ]; then
+		roflag=-r
+	else
+		roflag=-w
+	fi
+
+	# Get the loop filesystem type if not set
+	if [ -z "${LOOPFSTYPE}" ]; then
+	    FSTYPE=$(get_fstype "$loopfile")
+	else
+	    FSTYPE=${LOOPFSTYPE}
+	fi
+
+	# FIXME This has no error checking
+	modprobe loop
+	modprobe "${FSTYPE}"
+
+	# FIXME This has no error checking
+	if [ -z "${LOOPFLAGS}" ]; then
+		mount ${roflag} -o loop -t "${FSTYPE}" "$loopfile" "${rootmnt}"
+	else
+		mount ${roflag} -o loop -t "${FSTYPE}" "${LOOPFLAGS}" "$loopfile" "${rootmnt}"
+	fi
+
+	if [ -d "${rootmnt}/host" ]; then
+		mount -o move /host "${rootmnt}/host"
+	fi
+}
+
 # Mount the root file system.  It should be overridden by all
 # boot scripts.
 mountroot()
diff --git a/scripts/local b/scripts/local
index a103e68..2ef6413 100644
--- a/scripts/local
+++ b/scripts/local
@@ -170,7 +170,8 @@ local_mount_root()
 
 	local_premount
 
-	if [ "${readonly?}" = "y" ]; then
+	if [ "${readonly?}" = "y" ] && \
+	   { [ -z "$LOOP" ] || [ "${FSTYPE#ntfs}" = "$FSTYPE" ]; }; then
 		roflag=-r
 	else
 		roflag=-w
@@ -183,6 +184,10 @@ local_mount_root()
 	if ! mount ${roflag} ${FSTYPE:+-t "${FSTYPE}"} ${ROOTFLAGS} "${ROOT}" "${rootmnt?}"; then
 		panic "Failed to mount ${ROOT} as root file system."
 	fi
+
+	if [ "${LOOP}" ]; then
+		mount_loop_root
+	fi
 }
 
 local_mount_fs()
diff --git a/scripts/nfs b/scripts/nfs
index 40c92c7..dfa8e88 100644
--- a/scripts/nfs
+++ b/scripts/nfs
@@ -73,6 +73,10 @@ nfs_mount_root_impl()
 
 	# shellcheck disable=SC2086
 	nfsmount -o nolock ${roflag} ${NFSOPTS} "${NFSROOT}" "${rootmnt?}"
+
+	if [ "${LOOP}" ]; then
+		mount_loop_root
+	fi
 }
 
 # NFS root mounting
-- 
2.17.1