O_DIRECT wierd behavior..

From: Suresh Gopalakrishnan (gsuresh@cs.rutgers.edu)
Date: Sat Dec 15 2001 - 19:47:46 EST

I tried this small piece of code from an old post in the archive:

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

#define O_DIRECT 040000 /* direct disk access hint */

int main()
        char buf[16384];
        int fd;
        char *p;

        p = (char *)((((unsigned long)buf) + 8191) & ~8191L);
        fd = open("/tmp/blah", O_CREAT | O_RDWR | O_DIRECT);

        printf("write returns %i\n", write(fd, buf, 8192));
        printf("write returns %i\n", write(fd, p, 1));

        return 0;

Output is:

write returns -1
Filesize limit exceeded (core dumped)

$ ls -l /tmp/blah
---------- 1 gsuresh users 4294967274 Dec 15 19:15 /tmp/blah

The kernel is 2.4.16 and /tmp is ext2. (It runs fine on 2.4.2).

Any idea why this happens and how to fix this?


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This archive was generated by hypermail 2b29 : Sat Dec 15 2001 - 21:00:30 EST