am f84a5918: Merge "Use pread() in ZipFileRO for Linux" into gingerbread (2a877ed7) · Commits · e / os / android_frameworks_native-old

include/utils/ZipFileRO.h

+17 −7

Original line number	Diff line number	Diff line
		@@ -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 @@ typedef void* ZipEntryRO;
		* 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:

+32 −1

Original line number	Diff line number	Diff line
		@@ -508,6 +508,36 @@ bool ZipFileRO::getEntryInfo(ZipEntryRO entry, int* pMethod, size_t* pUncompLen,

		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);

		@@ -531,6 +561,7 @@ bool ZipFileRO::getEntryInfo(ZipEntryRO entry, int* pMethod, size_t* pUncompLen,
		return false;
		}
		}
		#endif /* HAVE_PREAD */

		off_t dataOffset = localHdrOffset + kLFHLen
		+ get2LE(lfhBuf + kLFHNameLen) + get2LE(lfhBuf + kLFHExtraLen);