nativelibc/posix-io/lseek.c

#include <windows.h>
#include <nt.h>
#include <unistd.h>

off_t lseek(int fd, off_t offset, int whence) {
	IO_STATUS_BLOCK io_status;
	FILE_POSITION_INFORMATION position;
	FILE_STANDARD_INFORMATION standard;
	long int status = NtQueryInformationFile((void *)fd, &io_status, &position, sizeof position, FilePositionInformation);
	if(status) return -1;
	switch(whence) {
		case SEEK_SET:
			position.CurrentByteOffset.QuadPart = offset;
			break;
		case SEEK_CUR:
			position.CurrentByteOffset.QuadPart += offset;
			break;
		case SEEK_END:
			status = NtQueryInformationFile((void *)fd, &io_status, &standard, sizeof standard, FileStandardInformation);
			if(status) return -1;
			position.CurrentByteOffset.QuadPart = standard.EndOfFile.QuadPart + offset;
			break;
		default:
			//errno = EINVAL;
			return -1;
	}
	status = NtSetInformationFile((void *)fd, &io_status, &position, sizeof position, FilePositionInformation);
	return status ? -1 : position.CurrentByteOffset.QuadPart;
}