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SubjectRe: Filesize limitation
On Tue, 4 Nov 1997, Rogier Wolff wrote:

> Richard B. Johnson wrote:
> >
> > On Mon, 3 Nov 1997, Andre Uratsuka Manoel wrote:
> >
> > >
> > > Hello gentlemen,
> > >
> > > I was contact by people asking about filesize limits in Linux as
> > > they tried to create a 2GB file, but couldn't. I figured the problem
> > > might be the filesize limitation. At least that is what I'd expect to
> > > happen with a file that size. Am I right on that? If it is so, is there
> > > a 64-bit filesystem for Linux?
> > >
> > There is plenty of "room" available in the object types that would
> > define a file in Linux for an ext2 file-system (like fpos_t, etc.)
>
> No there isn't.

yes there is - fpos_t is moving towards 64bit I think....
> > I don't have a spare disk large enough to make a 2Gb file. However,
>
> You don't need to. Make a file with a large hole in it.
>
> > I would guess that if you can't make one (with large enough media), there
> > is either a bug in the program that tries to create it or possibly a
> > bug in the kernel. You don't need 64 bits to manipulate a 2 Gb file.
>
> Nope. The minix filesystem limits you to 256Mb of file.
> The ext2fs limits you to 2G files.

No - it allows 64bit files :)
... providing the kernel can handle it though...
[afaik, but backed up by a thread a couple of months ago]

> Try the following:
>
> # create a file "testfile", seek to 2G-2Mb, write one Mb of zeroes.
> dd if=/dev/zero of=testfile seek=2046 bs=1024k count=1
> # OK.
>
> # Append some kilobytes of zeroes, until we hit the limit.
> dd if=/dev/zero bs=1k >> testfile
> # File too large after 1023 blocks output.

dd (or bash in this case) doesn't (yet) handle the large file access
sysctl's.... (llseek and friends :)
and as an "append to file" requires a lseek to the end of the file...
[incidentally, I can't remember why, but write() has this problem too]

> # See how much disk space this uses:
> ls -ls testfile
> # 2058 blocks on my system. Around 2Mb. Each of the two dd commands
> # generated an allocation of about 1Mb.
>
> Someone sent me a short DOS program to analyse an image today. My
> reaction was: I wouldn't write a program for that I should have a tool
> already on my system to do that. So I did. Same here. Enough tools
> available on a standard Linux box to experiment with from the command
> line.....

According to the thread I followed:
1. ext2fs is happy with 64bit limits
2. Linux/Alpha doesn't have a problem with this IIRC
3. The 64bit sysctls are still being built.....
(as a hint: they appeared in 2.1.60....)
4. glibc-2.1 will be the first system to support them (already do)
Now any and all of these could be wrong... But one clue: This thread
happened a month or three ago....
G'day, eh? :)
- Teunis

PS: glibc-2.1 isn't exactly common (yet). Most tools aren't linked to
that. Ergo most tools can't handle >2G files. Yet.
(though I suppose one could write one's own hooks into the large
filesystem support... :)


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