HP IO Accelerator for BladeSystem c-Class Performance Tuning Uživatelský manuál stáhnout pdf (Strana 27)

Programming using direct I/O 27

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;

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HP IO Accelerator for BladeSystem c-Class Performance Tuning Uživatelský manuál Strana 27