commit b1dbab45772beca259c60f704d33a215f8a8c2ca
author J. Richard Barnette <jrbarnette@chromium.org> Mon Jan 23 15:04:08 2012 -0800
committer Gerrit <chrome-bot@google.com> Mon Jan 23 17:36:31 2012 -0800
tree 22a7261ac42ec84a23500cc2ed56824e1e612f5a
parent 286a00661a371385ce5c125ceab8a91223bcdbdc

Fix a race condition when mounting loopback devices.

The previous code selected and configured the loopback device in two
separate stages.  This allowed for the possiblity that some other
code could claim the same loopback claimed by patch_kernel, leading
to failures.

BUG=chromium-os:24975
TEST=cros_generate_update_payload --output=<outfile> --image=<infile> --patch_kernel
TEST=image_to_live.sh

Change-Id: I5ea89f9e8519f1c02be22af3c172bfc7b52129ad
Reviewed-on: https://gerrit.chromium.org/gerrit/14646
Commit-Ready: Richard Barnette <jrbarnette@chromium.org>
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: David James <davidjames@chromium.org>

host/cros_generate_update_payload

diff --git a/host/cros_generate_update_payload b/host/cros_generate_update_payload
index af1c4bc..edbf303 100755
--- a/host/cros_generate_update_payload
+++ b/host/cros_generate_update_payload
@@ -47,7 +47,6 @@
 DST_KERNEL=""
 DST_ROOT=""
 STATE_MNT=""
-STATE_LOOP_DEV=""
 
 # Pass an arg to not exit 1 at the end
 cleanup() {
@@ -63,14 +62,10 @@
     DST_MNT=""
   fi
   if [ -n "$STATE_MNT" ]; then
-    sudo umount "$STATE_MNT"
+    sudo umount -d "$STATE_MNT" || true
     [ -d "$STATE_MNT" ] && rmdir "$STATE_MNT"
     STATE_MNT=""
   fi
-  if [ -n "$STATE_LOOP_DEV" ]; then
-    sudo losetup -d "$STATE_LOOP_DEV"
-    STATE_LOOP_DEV=""
-  fi
   rm -f "$SRC_KERNEL"
   rm -f "$SRC_ROOT"
   rm -f "$DST_KERNEL"
@@ -109,18 +104,14 @@
 
   echo "Patching kernel" $KERN_FILE
   echo "   into" $IMAGE
-  STATE_LOOP_DEV=$(sudo losetup -f)
-  [ -n "$STATE_LOOP_DEV" ] || die "no free loop device"
   local offset=$(partoffset "${IMAGE}" 1)
   offset=$(($offset * 512))
-  sudo losetup -o "$offset" "$STATE_LOOP_DEV" "$IMAGE"
   STATE_MNT=$(mktemp -d /tmp/state.XXXXXX)
-  sudo mount --read-only "$STATE_LOOP_DEV" "$STATE_MNT"
+  sudo mount -o ro,loop,offset=$offset "$IMAGE" "$STATE_MNT"
   dd if="$STATE_MNT"/vmlinuz_hd.vblock of="$KERN_FILE" conv=notrunc 2>/dev/null
-  sudo umount "$STATE_MNT"
+  sudo umount -d "$STATE_MNT"
+  rmdir "$STATE_MNT"
   STATE_MNT=""
-  sudo losetup -d "$STATE_LOOP_DEV"
-  STATE_LOOP_DEV=""
 }
 
 extract_kern_root() {