Support userspace-only disks

Commits e147e00 and c4f1bff in Ganeti add support for userspace-only
disks. That means that we could have an instance without a local
block device (e.g. using the embedded support in QEMU for rbd by
passing -drive file=rbd:pool/image_name without the need of a
/dev/rdbX device).

This patch does the following:

Introduce a find_disk() helper method that first checks the
DISK_IDX_PATH and if it is not exported then it returns
DISK_IDX_URI.

Introduce a losetup_disk() helper method that is used during
export/import and in case we have an ntfsdump/extdump image type.
Signed-off-by: Dimitris Aragiorgis <dimitris.aragiorgis@gmail.com>

snf-image-host/common.sh.in

@@ -102,7 +102,7 @@ get_api10_arguments() {
     esac
 
     instance=$INSTANCE_NAME
-    if [ $DISK_COUNT -lt 1 -o -z "$DISK_0_PATH" ]; then
+    if [ $DISK_COUNT -lt 1 ]; then
         log_error "At least one disk is needed"
         exit 1
     fi
@@ -111,15 +111,15 @@ get_api10_arguments() {
             log_error "Missing OS API Variable: \`EXPORT_DEVICE'"
             exit 1
         fi
-        blockdev=$EXPORT_DEVICE
+        export_disk=$EXPORT_DEVICE
     elif [ "$SCRIPT_NAME" = "import" ]; then
         if [ -z "$IMPORT_DEVICE" ]; then
             log_error "Missing OS API Variable: \`IMPORT_DEVICE'"
             exit 1
         fi
-        blockdev=$IMPORT_DEVICE
+        import_disk=$IMPORT_DEVICE
     else
-        blockdev=$DISK_0_PATH
+        disk0=$(find_disk 0)
     fi
     if [ "$SCRIPT_NAME" = "rename" -a -z "$OLD_INSTANCE_NAME" ]; then
         log_error "Missing OS API Variable: \`OLD_INSTANCE_NAME'"
@@ -213,6 +213,47 @@ format_disk0() {
 EOF
 }
 
+# This is used for export/import and in case we have an fsdump image type.
+# If the give disk is a block device this is a no-op.
+losetup_disk() {
+    local disk bdev
+
+    disk="$1"
+
+    if [ -b "$disk" ]; then
+        echo "$disk"
+    elif [ -f "$disk" ] ; then
+        bdev=$($LOSETUP --show -f "$disk")
+        add_cleanup $LOSETUP -d "$bdev"
+        echo $bdev
+    else
+        log_error "Cannot losetup $disk: not a regular file"
+        report_error "Could not use disk provided by Ganeti"
+        exit 1
+    fi
+}
+
+find_disk() {
+    local idx path uri
+
+    idx=$1
+
+    eval path=\$DISK_${idx}_PATH
+    eval uri=\$DISK_${idx}_URI
+
+    # Here we check if we have a valid disk path (block device or regular file)
+    if [ -b "$path" -o -f "$path" ]; then
+        echo $path
+    # Otherwise we choose the userspace URI and
+    # hope that snf-image can handle it
+    elif [ -n "$uri" ]; then
+        echo $uri
+    else
+        log_error "Disk information not exported by Ganeti"
+        exit 1
+    fi
+}
+
 create_floppy() {
     local img target IFS index name tm
 

snf-image-host/create

@@ -133,17 +133,12 @@ case $BACKEND_TYPE in
         ;;
 esac
 
-# If the target device is not a real block device we'll first losetup it.
-# This is needed for file disks.
-if [ ! -b "$blockdev" ]; then
-    original_blockdev="$blockdev"
-    blockdev=$($LOSETUP --show -f "$blockdev")
-    add_cleanup $LOSETUP -d "$blockdev"
-fi
-
 case "$IMAGE_TYPE" in
     ntfsdump|extdump)
-        # Create partitions
+        # Create a corresponding blockdev if required
+        blockdev=$(losetup_disk "$disk0")
+
+        # Create partitions on blockdev
         format_disk0 "$blockdev" "$IMAGE_TYPE"
 
         # Install a new MBR
@@ -159,7 +154,7 @@ case "$IMAGE_TYPE" in
         fi
         ;;
     diskdump)
-        target="$blockdev"
+        target="$disk0"
         ;;
     *)
         log_error "Unknown Image format: \`$IMAGE_TYPE'"

snf-image-host/export

@@ -26,11 +26,7 @@ ganeti_os_main
 
 # If the device we will export from, is not a real block device,
 # we'll first losetup it. This is needed for file disks.
-if [ ! -b "$blockdev" ]; then
-    original_blockdev="$blockdev"
-    blockdev=$($LOSETUP --show -f "$blockdev")
-    add_cleanup $LOSETUP -d "$blockdev"
-fi
+blockdev=$(losetup_disk "$export_disk")
 
 # Export disk's predicted size to Ganeti.
 # Used to provide a time estimate of the export process to the user.

snf-image-host/import

@@ -26,11 +26,7 @@ ganeti_os_main
 
 # If the device we will import to, is not a real block device,
 # we'll first losetup it. This is needed for file disks.
-if [ ! -b "$blockdev" ]; then
-    original_blockdev="$blockdev"
-    blockdev=$($LOSETUP --show -f "$blockdev")
-    add_cleanup $LOSETUP -d "$blockdev"
-fi
+blockdev=$(losetup_disk "$import_disk")
 
 $DD of="$blockdev" bs=4M
 

snf-image-host/kvm-common.sh

-# Copyright (C) 2013-2015 GRNET S.A. and individual contributors
+# Copyright (C) 2013-2016 GRNET S.A. and individual contributors
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -29,7 +29,7 @@ assign_disk_devices_to() {
 }
 
 launch_helper() {
-    local result_file result snapshot rc floppy i disk_path disks
+    local result_file result snapshot rc floppy i disks
 
     floppy="$1"
 
@@ -41,8 +41,7 @@ launch_helper() {
 
     disks=""
     for ((i=0; i < DISK_COUNT; i++)); do
-        eval disk_path=\"\$DISK_${i}_PATH\"
-        disks+=" -drive file=$disk_path,format=raw,if=virtio,cache=none"
+        disks+=" -drive file=$(find_disk $i),format=raw,if=virtio,cache=none"
     done
 
     set +e

snf-image-host/xen-common.sh

@@ -40,7 +40,7 @@ launch_helper() {
 
     set -- c d e f g h i j k l m n o p q r
     for ((i = 0; i < DISK_COUNT; i++)); do
-        eval disk_path=\"\$DISK_${i}_PATH\"
+        disk_path="$(find_disk $i)"
         case $(stat -L -c %F "$disk_path") in
         "regular file")
             ftype=file