Use pxelinux "ipappend" option to choose rootfs source

This fixes the issue described in the first 'netkeys' commit, where the
network would need to be available even when it was not used.

The "ipappend" option results in a $BOOTIF variable in the initrd
environment.  This variable is now used to determine whether to wait on
the network for a rootfs & keys, or to wait on the boot device becoming
available to determine whether it has the keys.

That is, there may or may not be a boot device which may or may not
have keys and/or rootfs, but we will always know for sure whether
it does, therefore there are no races and no waiting on the network
unnecessarily.

The qemu.sh script was updated to provide the BOOTIF variable when PXE
boot is emulated.

1 files changed, 15 insertions, 9 deletions

diff --git a/src/initrd/btrfs-create.sh b/src/initrd/btrfs-create.sh
index a1a53ed..8a0cd87 100644
--- a/src/initrd/btrfs-create.sh
+++ b/src/initrd/btrfs-create.sh
@@ -27,22 +27,28 @@ ceil4()
   printf '%d\n' "$x"
 }
 
+cdrom_has_rootfs()
+{
+    [ ! "$BOOTIF" ] || return
+    bootwait samizdat-cdrom
+    [ -d /cdrom/rootfs ]
+}
+
 losetup_layers()
 {
-    if netbooting; then
+    if cdrom_has_rootfs; then
+        local fs fs_rw
+        for fs in /cdrom/rootfs/*.btrfs; do
+            fs_rw=/"${fs##*/}".rw
+            dd if=/dev/zero of="$fs_rw" bs=1M count=10
+            losetup_snapshot "$fs" "$fs_rw" || return
+        done
+    else
         bootwait samizdat-nbd-dev
         dd if=/dev/zero of=/nbd0.rw bs=1M count=10
         dm_snapshot /dev/nbd0 /nbd0.rw
         return
     fi
-
-    bootwait samizdat-cdrom
-    local fs fs_rw
-    for fs in /cdrom/rootfs/*.btrfs; do
-        fs_rw=/"${fs##*/}".rw
-        dd if=/dev/zero of="$fs_rw" bs=1M count=10
-        losetup_snapshot "$fs" "$fs_rw" || return
-    done
 }
 
 init_samizdat()