android ota 增量包 升级失败

最近做ota增量包升级，
先编译好内核系统， 把整个系统烧入到机器，并制作update.zip .
修改内核，预制apk， 编译内核系统，制作update2.zip
制作差分包：

build/tools/releasetools/ota_from_target_files -v --block -p out/host/linux-x86 -k build/target/product/security/testkey -i update.zip update2.zip ota_update.zip

升级ota_update.zip .
失败。
在/cache/recovery/last_log 如下：
Finding update package...
I:Update location: /cache/update.zip
Opening update package...
I:read key e=3 hash=20
I:1 key(s) loaded from /res/keys
Verifying update package...
I:comment is 1738 bytes; signature 1720 bytes from end
I:whole-file signature verified against RSA key 0
I:verify_file returned 0
Installing update...
installing nexell.pyrope updater extensions
filename=EMMC:/dev/block/platform/dw_mmc.0/by-num/p1:18301148:96aceac9b90e93bd3caa7d505a0efb5091e6c7f8:18301148:59cc83d2f20b09300beabeecfeaf915e736af184
colons=5
pairs=2
Verifying current system...
i=2 ,partition=/dev/block/platform/dw_mmc.0/by-num/p1
zzh contents of partition "/dev/block/platform/dw_mmc.0/by-num/p1" didn't match EMMC:/dev/block/platform/dw_mmc.0/by-num/p1:18301148:96aceac9b90e93bd3caa7d505a0efb5091e6c7f8:18301148:59cc83d2f20b09300beabeecfeaf915e736af184
file "EMMC:/dev/block/platform/dw_mmc.0/by-num/p1:18301148:96aceac9b90e93bd3caa7d505a0efb5091e6c7f8:18301148:59cc83d2f20b09300beabeecfeaf915e736af184" doesn't have any of expected sha1 sums; checking cache
failed to stat "/cache/saved.file": No such file or directory
failed to load cache file
script aborted: "EMMC:/dev/block/platform/dw_mmc.0/by-num/p1:18301148:96aceac9b90e93bd3caa7d505a0efb5091e6c7f8:18301148:59cc83d2f20b09300beabeecfeaf915e736af184" has unexpected contents.
"EMMC:/dev/block/platform/dw_mmc.0/by-num/p1:18301148:96aceac9b90e93bd3caa7d505a0efb5091e6c7f8:18301148:59cc83d2f20b09300beabeecfeaf915e736af184" has unexpected contents.
E:Error in /cache/update.zip
(Status 7)

Installation aborted.
OTA failed! Please power off the device to keep it in this state and file a bug report!