Merge "refactored screenshot code" into gingerbread
diff --git a/include/utils/ZipFileRO.h b/include/utils/ZipFileRO.h
index e1ff780..3c1f3ca 100644
--- a/include/utils/ZipFileRO.h
+++ b/include/utils/ZipFileRO.h
@@ -14,13 +14,19 @@
* limitations under the License.
*/
-//
-// Read-only access to Zip archives, with minimal heap allocation.
-//
-// This is similar to the more-complete ZipFile class, but no attempt
-// has been made to make them interchangeable. This class operates under
-// a very different set of assumptions and constraints.
-//
+/*
+ * Read-only access to Zip archives, with minimal heap allocation.
+ *
+ * This is similar to the more-complete ZipFile class, but no attempt
+ * has been made to make them interchangeable. This class operates under
+ * a very different set of assumptions and constraints.
+ *
+ * One such assumption is that if you're getting file descriptors for
+ * use with this class as a child of a fork() operation, you must be on
+ * a pread() to guarantee correct operation. This is because pread() can
+ * atomically read at a file offset without worrying about a lock around an
+ * lseek() + read() pair.
+ */
#ifndef __LIBS_ZIPFILERO_H
#define __LIBS_ZIPFILERO_H
@@ -55,6 +61,10 @@
* the record structure. However, this requires a private mapping of
* every page that the Central Directory touches. Easier to tuck a copy
* of the string length into the hash table entry.
+ *
+ * NOTE: If this is used on file descriptors inherited from a fork() operation,
+ * you must be on a platform that implements pread() to guarantee correctness
+ * on the shared file descriptors.
*/
class ZipFileRO {
public:
diff --git a/libs/utils/ZipFileRO.cpp b/libs/utils/ZipFileRO.cpp
index bee86b2..9b1f82f 100644
--- a/libs/utils/ZipFileRO.cpp
+++ b/libs/utils/ZipFileRO.cpp
@@ -508,6 +508,36 @@
unsigned char lfhBuf[kLFHLen];
+#ifdef HAVE_PREAD
+ /*
+ * This file descriptor might be from zygote's preloaded assets,
+ * so we need to do an pread() instead of a lseek() + read() to
+ * guarantee atomicity across the processes with the shared file
+ * descriptors.
+ */
+ ssize_t actual =
+ TEMP_FAILURE_RETRY(pread(mFd, lfhBuf, sizeof(lfhBuf), localHdrOffset));
+
+ if (actual != sizeof(lfhBuf)) {
+ LOGW("failed reading lfh from offset %ld\n", localHdrOffset);
+ return false;
+ }
+
+ if (get4LE(lfhBuf) != kLFHSignature) {
+ LOGW("didn't find signature at start of lfh; wanted: offset=%ld data=0x%08x; "
+ "got: data=0x%08lx\n",
+ localHdrOffset, kLFHSignature, get4LE(lfhBuf));
+ return false;
+ }
+#else /* HAVE_PREAD */
+ /*
+ * For hosts don't have pread() we cannot guarantee atomic reads from
+ * an offset in a file. Android should never run on those platforms.
+ * File descriptors inherited from a fork() share file offsets and
+ * there would be nothing to protect from two different processes
+ * calling lseek() concurrently.
+ */
+
{
AutoMutex _l(mFdLock);
@@ -517,7 +547,7 @@
}
ssize_t actual =
- TEMP_FAILURE_RETRY(read(mFd, lfhBuf, sizeof(lfhBuf)));
+ TEMP_FAILURE_RETRY(read(mFd, lfhBuf, sizeof(lfhBuf)));
if (actual != sizeof(lfhBuf)) {
LOGW("failed reading lfh from offset %ld\n", localHdrOffset);
return false;
@@ -531,6 +561,7 @@
return false;
}
}
+#endif /* HAVE_PREAD */
off_t dataOffset = localHdrOffset + kLFHLen
+ get2LE(lfhBuf + kLFHNameLen) + get2LE(lfhBuf + kLFHExtraLen);