The first glibc 2.2 backwards compatbility problem....

[tytso@mit.edu]

So here's the first glibc 2.2 backwards compatiblity problem that's come
up, according to HJ Lu.....

>RedHat 7.0 uses glibc 2.2. There are some subtle changes from glibc
>2.1 to 2.2. One of them is errno. From the glibc manual:
>
>     The initial value of `errno' at program startup is zero.  Many
>     library functions are guaranteed to set it to certain nonzero
>     values when they encounter certain kinds of errors.  These error
>     conditions are listed for each function.  These functions do not
>                                               ^^^^^^^^^^^^^^^^^^^^^^
>     change `errno' when they succeed;
>     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
>This is no longer true in glibc 2.2. `errno' can change after the
>return from a glibc function, successful or not. Any applications
>depending the old documented glibc behavior may fail with glibc 2.2.
>So far, I have found elm is one of them:
>
>http://sources.redhat.com/ml/libc-hacker/2000-09/msg00134.html
>
>I don't like this change. My concern is although the glibc manual
>shouldn't have said "These functions do not change `errno' when they
>succeed;" in the first place, changing the application source code
>may not be an option for every Linux user. Glibc has to provide the
>backward compatibility on this. But most of glibc developers don't
>share my view.

What if anything should we say in the specification about this?   If we
decide to use glibc 2.2 as our base specification, I think we're going
to need to start an appendix listing differences between glibc 2.1 and
2.2.  I ***hope*** that there aren't too many of these compatibility
land mines hiding in glibc 2.2.   

						- Ted

P.S.  My other big concern is that RedHat apparently shipped a
pre-release of 2.2 (i.e., 2.1.91).  Given that Ulrich works for RedHat I
hope that someone at RH got Ulrich to sign a contract in blood stating
that there will be no compatibility problems introduced between 2.1.91
and 2.2.  Otherwise, this has the potential for causing a really big
mess.....