Adding a build id check to blob cache.

Add a build id field to the header structure in blob cache. Add build
id support with reading and writing the cache. When the cache gets
written it writes the build id at the end of the header. When read it
checks to see if there is a match between the current version and the
version in the cache. If not, it invalidates the cache which would
typically only occur during an ota update.  Also remove blob cache
from the host build.

bug: 18262905

Change-Id: I753b1de1986703a4c1c8691b9d2bb533b2546143

1 files changed, 14 insertions, 5 deletions

diff --git a/libutils/BlobCache.cpp b/libutils/BlobCache.cpp
index 0ea09cf..126995b 100644
--- a/libutils/BlobCache.cpp
+++ b/libutils/BlobCache.cpp
@@ -25,13 +25,15 @@
 #include <utils/Errors.h>
 #include <utils/Log.h>
 
+#include <cutils/properties.h>
+
 namespace android {
 
 // BlobCache::Header::mMagicNumber value
 static const uint32_t blobCacheMagic = ('_' << 24) + ('B' << 16) + ('b' << 8) + '$';
 
 // BlobCache::Header::mBlobCacheVersion value
-static const uint32_t blobCacheVersion = 2;
+static const uint32_t blobCacheVersion = 3;
 
 // BlobCache::Header::mDeviceVersion value
 static const uint32_t blobCacheDeviceVersion = 1;
@@ -165,7 +167,7 @@ static inline size_t align4(size_t size) {
 }
 
 size_t BlobCache::getFlattenedSize() const {
-    size_t size = align4(sizeof(Header));
+    size_t size = align4(sizeof(Header) + PROPERTY_VALUE_MAX);
     for (size_t i = 0; i < mCacheEntries.size(); i++) {
         const CacheEntry& e(mCacheEntries[i]);
         sp<Blob> keyBlob = e.getKey();
@@ -187,10 +189,13 @@ status_t BlobCache::flatten(void* buffer, size_t size) const {
     header->mBlobCacheVersion = blobCacheVersion;
     header->mDeviceVersion = blobCacheDeviceVersion;
     header->mNumEntries = mCacheEntries.size();
+    char buildId[PROPERTY_VALUE_MAX];
+    header->mBuildIdLength = property_get("ro.build.id", buildId, "");
+    memcpy(header->mBuildId, buildId, header->mBuildIdLength);
 
     // Write cache entries
     uint8_t* byteBuffer = reinterpret_cast<uint8_t*>(buffer);
-    off_t byteOffset = align4(sizeof(Header));
+    off_t byteOffset = align4(sizeof(Header) + header->mBuildIdLength);
     for (size_t i = 0; i < mCacheEntries.size(); i++) {
         const CacheEntry& e(mCacheEntries[i]);
         sp<Blob> keyBlob = e.getKey();
@@ -239,15 +244,19 @@ status_t BlobCache::unflatten(void const* buffer, size_t size) {
         ALOGE("unflatten: bad magic number: %" PRIu32, header->mMagicNumber);
         return BAD_VALUE;
     }
+    char buildId[PROPERTY_VALUE_MAX];
+    int len = property_get("ro.build.id", buildId, "");
     if (header->mBlobCacheVersion != blobCacheVersion ||
-            header->mDeviceVersion != blobCacheDeviceVersion) {
+            header->mDeviceVersion != blobCacheDeviceVersion ||
+            len != header->mBuildIdLength ||
+            strncmp(buildId, header->mBuildId, len)) {
         // We treat version mismatches as an empty cache.
         return OK;
     }
 
     // Read cache entries
     const uint8_t* byteBuffer = reinterpret_cast<const uint8_t*>(buffer);
-    off_t byteOffset = align4(sizeof(Header));
+    off_t byteOffset = align4(sizeof(Header) + header->mBuildIdLength);
     size_t numEntries = header->mNumEntries;
     for (size_t i = 0; i < numEntries; i++) {
         if (byteOffset + sizeof(EntryHeader) > size) {