Re: files of size larger than fs size

[Dave Kleikamp <shaggy@austin.ibm.com>]

On Wed, 2005-03-16 at 20:52 -0800, Max wrote:
> Bryan,
> 
> I'm not experienced in filesystems. But I've derived the testcase
> program from some buggy application that occasionally created huge
> files on my fs. That was not so easy to reproduce since not every
> sequence of seeks/reads/writes results in a huge file. But finally I
> got it 100% reproducible.
> 
> So I would appriciate if somebody make any good from that testcase
> code.

man lseek tells you to test the return code against (off_t)-1.  I found
that for larger values, your test program is returning -1, but unsigned
it appears as 18446744073709551615.

> 
> Different filesizes look strange to me. What I have so far:
> 
> JFS:    281474976706576  =  2**48 - 4080
> XFS:  72057594037923856  =  2**56 - 4080
> EXT3:     1099511627784  =  2**40 + 8

I can speak for jfs, and it supports file sizes up to 2**52.  It uses 40
bits to address the logical block offset within a file with a 4K (2**12)
size block.  The individual file systems set sb->s_maxbytes to the
appropriate value.

> Thanks,
> Max
> 
> P.S. direct link to the testcase program: http://bugzilla.kernel.org/attachment.cgi?id=4729

-- 
David Kleikamp
IBM Linux Technology Center