Re: 2.4 and 2GB swap partition limit

Andi Kleen
2001-05-04T08:17:23Z

On Wed, May 02, 2001 at 04:17:21PM -0600, Andreas Dilger wrote:
> Andi Kleen writes:
> > On Mon, Apr 30, 2001 at 12:07:44PM -0700, David S. Miller wrote:
> > But something must have been not working with it for mmaps/shlibs
> > (not executables); at least historically.
> > At least I remember that all hell broke lose when you tried to update
> > libc by cp'ing a new one to /lib/libc.so in the 1.2 days. cp should create a
> > new inode (it uses O_CREAT) so in theory it should be coherent by the inode
> > reference; but somehow it didn't use to work and random already running
> > programs started to segfault. This was long ago. I wonder if old
> > GNU cp used O_TRUNC instead of O_CREAT, or was there some other kernel bug
> > with mappings (hopefully long since fixed). Anybody remembers?
>
> No, "cp" is still not a safe way to update libc, and I doubt it ever will be.
> cp does _not_ create a new inode (unlike mv), so you are writing "garbage"
> into the currently running executables.

Ok, the bug is that executable shlibs mappings do not get EBUSY as when you try
to write into a running executable and it's still not fixed.

> NB: my open(2) says for O_CREAT "If the file does not exist it will be
> created". This is _not_ the same as O_EXCL, which will only mean that
> open(2) will fail when it tries to create a new file.

I assumed it would just create a new inode; but seems I was wrong.
Thanks for the clarification.

-Andi