64 Bits from Larry McVoy

Jim Nance (jlnance@avanticorp.com)
Mon, 4 Nov 1996 08:02:36 -0500 (EST)

Forwarded message:

> Linux is 64 bit in that the types are right. Linux is not 64 bit in that
> the file systems don't support >32 bit offsets (something that wouldn't
> be hard to fix, sounds like a version number on ext2fs).

Well Larry,
I was almost sure you were wrong, so I wrote the following test program.
Unfortunatly, I did manage to tickle enough linux bugs so that you can
claim you are right :-) So instead of claiming victory, I will submit
a bug report :-( For those intrested in reproducing this, I am running
Redhat 4.0 with redhats kernel, and the partition I am working contains an
800MB ext2 file system. Here is the program. It tries to make a large
sparse file:

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

#define GB ((long)(1024*1024*1024)/2)
#define NG (20L)

int main()
{
off_t offset;
int fd = open("bigfile", O_CREAT|O_TRUNC|O_WRONLY);

if(fd<0) {perror("open:"); exit(1);}

for(offset=0; offset<NG*GB; offset += GB) {
int num;
off_t pos = lseek(fd, offset, SEEK_SET);
if(pos!=offset) {perror("lseek:"); exit(1);}
num=write(fd,"x",1);
if(num!=1) {perror("write:"); exit(1);}
}

printf("Done!");
return 0;
}

The first thing to notice is that I have divided GB by 2. If I don't do
this the program fails after making a 1G file, and I get a nice printk()
from the ext2fs. So I divided by two and reran. Now I can make a very
large file, but something is still wrong:

total 76
-rwxrwxrwx 1 jlnance users 14378 Nov 4 07:39 a.out*
-rw-rw-rw- 1 jlnance users 544 Nov 4 07:38 big.c
-r-xrwS--T 1 jlnance users 10200547329 Nov 4 07:43 bigfile*

I don't know how the S--T bits got set on bigfile, but I certainly did
not mean to do it. I have also found that if I do much in the directory
containing bigfile, its size will eventually shrink down to 1.6G.

Anyone have any ideas?

Jim

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