#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

int main( int argc, char **argv )
{
    int fd;
    off_t *offsets;
    struct stat sb;
    int numReads = 1024;

    // get page-sized buffer (Linux direct IO
    // fails unless IO requests are exact
    // multiples of page size)
    size_t readSize = sysconf( _SC_PAGESIZE );

    // get page-aligned buffer (Linux can't handle
    // direct IO unless it's page-aligned)
    char *buffer = valloc( readSize );

    // must actually touch the memory to create
    // the physical page mapping in the process
    // address space
    memset( buffer, 0, readSize );

    // get an array for offsets to read from, since
    // calling lrand48() during the read loop can
    // be slow enough to impact the results, especially
    // on fast devices
    offsets = ( off_t * ) calloc( numReads, sizeof( offsets[ 0 ] ) );

    // need to do direct IO to avoid page cache
#ifdef __linux
    fd = open( argv[ 1 ], O_RDONLY | O_DIRECT );
#else
    fd = open( argv[ 1 ], O_RDONLY );
#endif

#ifdef __sun
    directio( fd, DIRECTIO_ON );
#endif

    fstat( fd, &sb );

    for ( ii = 0; ii < numReads; ii++ )
    {
        // get a random offset that's no larger
        // than the file/device we're reading
        offsets[ ii ] = ( off_t ) lrand48();
        offsets[ ii ] <<= 32;
        offsets[ ii ] += ( off_t ) lrand48();
        offsets[ ii ] %= sb.st_size;
        // mask to get 512-byte offsets
        offsets[ ii ] &= ( off_t ) 0xFFFFFFFFFFFFFE00;
    }

    // do the reads
    // add code to get start time here
    for ( ii = 0; ii < numReads, ii++ )
    {
        pread( fd, buffer, readSize, offsets[ ii ] );
    }
    // add code to get finish time here, then
    // print out results
    
    return( 0 );
}

./RandomIOTest /dev/sda1

./RandomIOtest /dev/rdsk/c1t2d4s2