HP c-Class Performance Tuning manual Programming using direct I/O

int open(char* filename);

int write(char* buf, int size_t); int close();

size_t gbytesWritten() { return bytes_written / 1000 / 1000 / 1000; } private:

int fd;

size_t bytes_written; };

int DirectFile::open(char* filename) { int ret = 0;

fd = ::open(filename, O_DIRECT O_WRONLY, S_IRUSR S_IWUSR S_IRGRP); if( fd == -1 ) {

ret = -1;

}

bytes_written = 0; return ret;

}

int DirectFile::write(char* buf, int bufsize) {

int written = pwrite(fd, buf, bufsize, bytes_written); if( written >= 0 )

bytes_written += written; return written;

}

int main( int argc, char **argv) { char* buf;

int ret = 0; enum { numpages = 256, };

int pagesize = getpagesize();

int bufsize = pagesize * numpages;

if( ret = posix_memalign((void**)&buf, pagesize, bufsize) ) { cerr << "Memalign failed" << endl;

exit(ret);

}

memset(buf, 0xaa, bufsize); DirectFile file;

if( file.open(FILENAME) ) {

cerr << "Open of " << FILENAME << " failed" << endl;

Programming using direct I/O 27