- // If the file is large, try to use mmap to read it in. We don't use mmap
- // for small files, because this can severely fragment our address space. Also
- // don't try to map files that are exactly a multiple of the system page size,
- // as the file would not have the required null terminator.
- //
- // FIXME: Can we just mmap an extra page in the latter case?
- if (FileSize >= 4096*4 &&
- (FileSize & (sys::Process::GetPageSize()-1)) != 0) {
- if (const char *Pages = sys::Path::MapInFilePages(FD, FileSize)) {
- return GetNamedBuffer<MemoryBufferMMapFile>(StringRef(Pages, FileSize),
- Filename);
+ // Don't try to map files that are exactly a multiple of the system page size
+ // if we need a null terminator.
+ if ((FileSize & (PageSize -1)) == 0)
+ return false;
+
+ return true;
+}
+
+error_code MemoryBuffer::getOpenFile(int FD, const char *Filename,
+ OwningPtr<MemoryBuffer> &result,
+ uint64_t FileSize, uint64_t MapSize,
+ int64_t Offset,
+ bool RequiresNullTerminator) {
+ static int PageSize = sys::Process::GetPageSize();
+
+ // Default is to map the full file.
+ if (MapSize == uint64_t(-1)) {
+ // If we don't know the file size, use fstat to find out. fstat on an open
+ // file descriptor is cheaper than stat on a random path.
+ if (FileSize == uint64_t(-1)) {
+ struct stat FileInfo;
+ // TODO: This should use fstat64 when available.
+ if (fstat(FD, &FileInfo) == -1) {
+ return error_code(errno, posix_category());
+ }
+ FileSize = FileInfo.st_size;
+ }
+ MapSize = FileSize;
+ }
+
+ if (shouldUseMmap(FD, FileSize, MapSize, Offset, RequiresNullTerminator,
+ PageSize)) {
+ off_t RealMapOffset = Offset & ~(PageSize - 1);
+ off_t Delta = Offset - RealMapOffset;
+ size_t RealMapSize = MapSize + Delta;
+
+ if (const char *Pages = sys::Path::MapInFilePages(FD,
+ RealMapSize,
+ RealMapOffset)) {
+ result.reset(GetNamedBuffer<MemoryBufferMMapFile>(
+ StringRef(Pages + Delta, MapSize), Filename, RequiresNullTerminator));
+ return error_code::success();