Lustre discuss - May 2006 - Error with O_DIRECT on Lustre

Is O_DIRECT supported on Lustre for write()?

I got an EINVAL error when I write to a file opened with mode O_DIRECT. 
The write amount is the same as the file system block size, which is 4MB 
on the machine I ran. According to Lustre manual, this should be fine as 
long as the I/O is aligned with 512B. Read is fine, though.

Attached is the the code.  I compiled it with gcc.

Wei-keng
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#include <stdio.h>
#include <stdlib.h>

#define __USE_GNU
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>   /* __USE_GNU to use O_DIRECT defined in bits/fcntl.h
*/
#include <unistd.h>

#include <errno.h>
extern int errno;

/*---< main()
>-------------------------------------------------------------*/
int main(int argc, char **argv)
{
    int         i, err, fd, block_size;
    mode_t      io_mode;
    char       *buf, *filename;
    long long   offset = 0;
    struct stat statBuf;

    filename = "/cfs/projects/widescratch/users/wkliao/testfile.dat";

    /* get system block size */
    stat(filename, &statBuf);
    block_size = statBuf.st_blksize;
    printf("Writing to file: %s  
block_size=%d\n",filename,block_size);

    buf = (char*) malloc(block_size);
    for (i=0; i<block_size; i++) buf[i] = ''z'';

    io_mode = O_CREAT | O_WRONLY | O_DIRECT;

    fd = open(filename, io_mode, 0600);
    if (fd == -1) printf("Error when open file %s\n", filename);

    err = write(fd, buf, block_size);
    if (err == -1)
        printf("WRITE Error: offset=%lld len=%d -
errno=%d(EINVAL=%d)\n",offset,block_size,errno,EINVAL);
    else
        printf("WRITE Success: offset=%lld len=%d
err=%d\n",offset,block_size,err);
    else
        printf("WRITE Success: offset=%lld len=%d
err=%d\n",offset,block_size,err);

    close(fd);
    free(buf);
    return 0;
}