[lustre-discuss] Hole Identification in file

[lokesh jaliminche]

Hi,

Does lustre support SEEK_HOLE/SEEK_DATA flag for lseek?

I did some experiment with the below program to find out if lustre supports
SEEK_HOLE and SEEK_DATA flag. I found that lustre always returns the end of
the file for SEEK_HOLE and 0 for SEEK_DATA and as per the man page this is
the simplest implementation that file system can have(If they dont want to
support these flags). So just wanted to confirm.

Program :
========
#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#define SEEK_OFF 10485760
int main()
{
    int fd;
    char buffer[80];
    int i = 0;
    static char message[]="Hello world";
    fd=open("myfile", O_RDWR);
    if (fd != -1)
        return 1;
    printf("creating hole by writing at each of %d strides\n", SEEK_OFF);
    for (i = 1; i < 10; i++)
    {
        int seek_off = i * SEEK_OFF;
        int sz;
        printf("seek_off %ld\n", lseek(fd, seek_off, SEEK_SET));
        sz = write(fd,message,sizeof(message));
        printf("write size = %d\n", sz);
        printf("String : %s\n", message);
    }
    printf("Demonstrating SEEK_HOLE and SEEK_DATA %d \n", SEEK_OFF);
    int start_off = 0;
    lseek(fd, 0, SEEK_SET);
    printf("after SEEK_HOLE start_off %ld\n", lseek(fd, 0, SEEK_HOLE));
    printf("after SEEK_DATA start_off %ld\n", lseek(fd, start_off,
SEEK_DATA));
    printf("after SEEK_HOLE start_off %ld\n", lseek(fd, 10485760,
SEEK_HOLE));
    printf("after SEEK_DATA start_off %ld\n", lseek(fd, (10485760 *2 ),
SEEK_DATA));
    close(fd);
}

output:
=====
after SEEK_HOLE start_off 94372142
after SEEK_DATA start_off 0
after SEEK_HOLE start_off 94372142
after SEEK_DATA start_off 0

Regards,
Lokesh
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