live: mount ISO squashfs directly out of the rootfs image

cosa now uses identical initramfs and rootfs images in the PXE and ISO
artifacts.  Instead of expecting /root.squashfs, find the rootfs image
in the ISO pxeboot directory and mount the squashfs from a fixed offset
in the cpio archive.  Use the existence of the coreos.liveiso= karg,
rather than a flag file, to detect that we're ISO-booted.  In ISO mode,
use bsdtar to read the osmet files out of the rootfs image.

overlay.d/05core/usr/lib/dracut/modules.d/20live/coreos-liveiso-persist-osmet.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=Persist osmet files (ISO)
+DefaultDependencies=false
+ConditionPathExists=/run/ostree-live
+ConditionKernelCommandLine=coreos.liveiso
+RequiresMountsFor=/run/media/iso
+Before=initrd-switch-root.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=/usr/bin/mkdir -p /run/coreos-installer/osmet
+# bsdtar reads cpio archives, and unlike cpio(1L), knows how to seek over
+# members it isn't reading
+ExecStart=/usr/bin/bsdtar -x -C /run/coreos-installer/osmet -f /run/media/iso/images/pxeboot/rootfs.img *.osmet

overlay.d/05core/usr/lib/dracut/modules.d/20live/coreos-live-persist-osmet.service → overlay.d/05core/usr/lib/dracut/modules.d/20live/coreos-livepxe-persist-osmet.service

@@ -1,9 +1,11 @@
 [Unit]
-Description=Persist osmet files
+Description=Persist osmet files (PXE)
 DefaultDependencies=false
 ConditionPathExists=/run/ostree-live
+ConditionKernelCommandLine=!coreos.liveiso
 # Downloads and unpacks the osmet files if not already appended
 After=coreos-livepxe-rootfs.service
+Before=initrd-switch-root.target
 
 [Service]
 Type=oneshot

overlay.d/05core/usr/lib/dracut/modules.d/20live/coreos-livepxe-rootfs.service

@@ -3,7 +3,7 @@ Description=Acquire live PXE rootfs image
 DefaultDependencies=false
 ConditionPathExists=/usr/lib/initrd-release
 ConditionPathExists=/run/ostree-live
-ConditionPathExists=/etc/coreos-live-want-rootfs
+ConditionKernelCommandLine=!coreos.liveiso
 
 After=basic.target
 # Network is enabled here

overlay.d/05core/usr/lib/dracut/modules.d/20live/live-generator

@@ -52,9 +52,10 @@ ExecStartPre=/usr/sbin/ostree-cmdline start
 ExecStartPost=/usr/sbin/ostree-cmdline stop
 EOF
 
-# In this case, the rootfs is already unpacked into the initrd, or we need
-# to retrieve it
-if [ -f /etc/coreos-live-want-rootfs ]; then
+isoroot=$(getarg coreos.liveiso= ||:)
+if [ -z "${isoroot}" ]; then
+    # In this case, the rootfs is already unpacked into the initrd, or we need
+    # to retrieve it
     cat >"${UNIT_DIR}/sysroot.mount" <<EOF
 # Automatically generated by live-generator
 
@@ -70,12 +71,6 @@ Where=/sysroot
 Type=squashfs
 EOF
 else
-    isoroot=$(getarg coreos.liveiso=)
-    if [ -z "${isoroot}" ]; then
-        echo "Missing required coreos.liveiso kernel argument" 1>&2
-        exit 1
-    fi
-
     # And in this case, it's on the ISO
     mkdir -p /run/media/iso
     isosrc=dev/disk/by-label/${isoroot}
@@ -113,9 +108,13 @@ Before=initrd-root-fs.target
 RequiresMountsFor=/run/media/iso
 
 [Mount]
-What=/run/media/iso/root.squashfs
+What=/run/media/iso/images/pxeboot/rootfs.img
 Where=/sysroot
 Type=squashfs
+# Offset of the squashfs within the rootfs cpio.  Assumes newc format
+# and that a file named "root.squashfs" is the first member.  This offset
+# is checked by coreos-assembler cmd-buildextend-live at build time.
+Options=offset=124
 EOF
 fi
 

overlay.d/05core/usr/lib/dracut/modules.d/20live/module-setup.sh

@@ -41,7 +41,10 @@ install() {
     install_and_enable_unit "coreos-live-clear-sssd-cache.service" \
         "ignition-complete.target"
 
-    install_and_enable_unit "coreos-live-persist-osmet.service" \
+    install_and_enable_unit "coreos-liveiso-persist-osmet.service" \
+        "default.target"
+
+    install_and_enable_unit "coreos-livepxe-persist-osmet.service" \
         "default.target"
 
     inst_simple "$moddir/coreos-liveiso-reconfigure-nm-wait-online.service" \