Merge "Use pread() in ZipFileRO for Linux" into gingerbread (08599621) · Commits · e / os / platform_frameworks_native

include/utils/ZipFileRO.h

+17 −7

Original line number	Original line	Diff line number	Diff line
	@@ -14,13 +14,19 @@
	* limitations under the License.		* limitations under the License.
	*/		*/

	//		/*
	// Read-only access to Zip archives, with minimal heap allocation.		* Read-only access to Zip archives, with minimal heap allocation.
	//		*
	// This is similar to the more-complete ZipFile class, but no attempt		* This is similar to the more-complete ZipFile class, but no attempt
	// has been made to make them interchangeable. This class operates under		* has been made to make them interchangeable. This class operates under
	// a very different set of assumptions and constraints.		* 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		#ifndef __LIBS_ZIPFILERO_H
	#define __LIBS_ZIPFILERO_H		#define __LIBS_ZIPFILERO_H

	@@ -55,6 +61,10 @@ typedef void* ZipEntryRO;
	* the record structure. However, this requires a private mapping of		* the record structure. However, this requires a private mapping of
	* every page that the Central Directory touches. Easier to tuck a copy		* every page that the Central Directory touches. Easier to tuck a copy
	* of the string length into the hash table entry.		* 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 {		class ZipFileRO {
	public:		public:

libs/utils/ZipFileRO.cpp

+32 −1

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

	unsigned char lfhBuf[kLFHLen];		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);		AutoMutex _l(mFdLock);

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

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