RFC: library conventions for libc5 and libc6 in hamm Take 4
Hello!
I incorporated the changes mentioned by Mark Eichin.
Furthermore I noticed that there were several issues that have not
been handlied by this proposal, so I added several sections.
These tell how to handle dependences and conflicts, source packages
and bugfixes for bo. This is a lot of new stuff. Please read it
carefully and tell me where I messed up.
Helmut
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Debian library policy supplement draft for libc5->libc6 migration
This document is meant to tell what a Debian package providing a
library should do to support both libc6 (glibc2) and libc5.
Note that these requirements are for Debian 2.0 (codename hamm).
Contents
1. Run time packages
2. Development packages
3. Source packages
4. Requirements on libraries for Debian 2.0
5. Conflicts and Dependencies
6. Handling bugfix releases for Debian 1.3 (bo)
7. Requirements on compiler packages
1. Run time packages
A package providing a shared library has to support both C library
packages, libc5 and libc6 based libraries. This must be done using
two Debian packages, each depending on the correct C library
package.
The package naming convention currently suggests to name these
packages as follows. Some packages (mostly from base) may use
locations in /lib.
based on | package name | library location
--------------------------------------------
libc6 | libfoog [1]| /usr/lib/libfoo.so.<ver>
libc5 | libfoo | /usr/lib/libc5-compat/libfoo.so.<ver> [2]
If a library runtime package contains files that are needed by
both versions of the library, a new package should be made for
just these files that both other packages depend on.
This package naming convention does _not_ apply if a package uses
different sonames for libc5 and libc6 based packages
There are two exceptions from this rule. The shared linker
ld-linux.so.1 and the C library files libc.so.5 and libm.so.5
should still be located in /lib, not in /lib/libc5-compat.
Packages based on X have to use /usr/X11R6 as prefix, not /usr.
Note that the X libraries are designed to work with both C libraries.
2. Development packages
The Debian policy requires that all files needed for compiling/linking
other packages with the library are in a separate package, the
development package. Up to now this package simply was called
libfoo-dev. As packages based on libc5 and libc6 usually cannot
use the same development files there has to be a clear statement
how to separate these. So for now the following packages are
required:
based on | package name | hierarchy locations
---------------------------------------------------------------
libc6 | libfoog-dev | /usr/{lib,include}
libc5 | libfoo-altdev | /usr/<a>-linuxlibc1/{lib,include}
Note that <a> usually is i486, but may not be hardcoded in
debian/rules. It should be obtained using
dpkg --print-gnu-build-architecture
Remember that the libfoo-altdev package has to include symlinks
/usr/<a>-linuxlibc1/lib/libfoo.so -> /usr/lib/libc5-compat/libfoo.so.<ver>
to enable using the shared libraries when compiling.
All documentation that is not depending on whether the library was
compiled for libc5 or for libc6 should be either part of the
libfoog-dev package or be put into a separate package if it is
large. In particular this includes manpages which _have_ to be part
of the libfoog-dev package.
Note that the choice to base Debian 2.0 on libc6 fixed the fact
that the main locations will be used for libc6 packages. The
alternate locations are used for libc5 based packages.
This decision does not necessarily mean that by default the
compiler uses the libc6 packages, please read section 4 for more
information. Using a four-way approach for library locations
(standard and alternate locations for libc6 and libc5 based
packages) will make Debian systems inconsistent with each other,
something we should avoid at (nearly) all costs.
3. Source packages
The source package name should _not_ be modified for hamm.
If a bugfix for bo has to be released, use bo's source package to
extract the bo source and add for each hamm release a line to
debian/changelog stating that this release was a hamm release.
Make your bugfix changes, including changes to the control file
according to section 6.
Then unpack the hamm source again, update debian/changelog and
debian/control to figure the bo release, and release a new hamm
package (including the bugfix, if it affects hamm as well). [3]
4. Requirements on libraries for Debian 2.0
Libraries (regardless of which library they're compiled against) need
to have runtime dependencies on one of libc, libdl or libm to enable
the shared linker to determin which library to use for a binary.
These runtime dependencies are _NOT_ dependencies in the Debian
way, but dependencies generated by the linker when generating the
shared library. See the binutils manual for more information.
In general we want libraries compiled for libc6 to be thread-safe.
This is, however, not practical or feasible for every library
package. Making a library thread-safe involves quite a lot of work,
much of it nontivial.
Thread-safe means that the following changes must be made to the
library packages:
- compile the library using -D_RENTRANT or -D_THREAD_SAFE
- there may be no permanent data residing in the library memory that
can be different for different threads.
this means in the first place no static or global variables that
are not in some way protected from access by a different threads
via mutexes.
- all write access to files from a library must be both protected
using some file locking mechanism in addition to using mutexes.
- at least some library functions must be protected from being
used at the same time by two threads sharing the same memory
space. This is done using mutexes.
As these usually are all nontrivial changes to a library if it isn't
thread-safe already (in which case just using -D_RENTRANT should
be used in addition to whatever the library uses to support threads),
I suggest that noone starts doing this without getting in contact with
the upstream maintainer(s).
If a library has a thread-safe version, the debian package should
use this. The performance deficits usually are very small when not
linking to libpthreads so only if there are serious reasons, the
debian package may include the non-thread-safe version.
There will be a list available that lists all libraries part of
Debian and their current status regarding compliance with these
standard requirements. This list will be posted regularly to
debian-devel by Helmut Geyer <Helmut.Geyer@iwr.uni-heidelberg.de>.
5. Conflicts & Dependencies for hamm packages
The libfoog package _has_ to conflict with all versions of the
libfoo package before it was made to use the libc5-compat
directory. Furthemore it should depend on libc6.
The libfoog-dev package must depend on libc6-dev and the libfoog
package of the same release. It has to conflict with the libfoo-dev
package.
The hamm libfoo package has to depend on libc6 and has to conflict
with libfoo-dev and libc5-dev.
The libfoo-altdev package has to depend on the libc5-altdev and
libfoo package of the same release.
6. Handling bugfixes for Debian 1.3 (bo)
Using the dependencies from Section 5. there will be problems with
making bugfix releases for bo. These have to be handled carefully
as otherwise there may be tremendous problems for people using
hamm systems.
As there is one package name used for both hamm and bo that stays
the same (libfoo), we have to very careful.
The following steps should be followed:
i) when making a bo bugfix release, be sure to make a hamm release
at the same time, using a higher release number for the hamm
release. Update the hamm package's conflicts according to
section 5.
ii) Any bo package for libfoo _has_ to conflict with libc6,
libfoo-altdev and libfoog.
iii)The libfoo-dev package has to conflict with libc5-altdev and
has to depend on libc5-dev.
7. Requirements on compiler packages
The compiler and binutils packages have to provide working
development environments for both C libraries. Basically (that is
from the compiler standpoint) there is no real difference between
the two environments, only some paths and automatic definitions
have to be changed. All this can be done (and is in fact done) by
supplying a different specs file in a different location.
The gcc packages do this as follows:
The gcc package uses libc6 by default and is installed in /usr/bin.
The alt-gcc package uses libc5 by default and is located in
/usr/i486-linuxlibc1/bin. By prepending this to the path this can
be made the default.
These requirements are fulfilled by the current gcc packages.
Remarks:
[1] the name of a library package often includes the major version
number of the library. If so, the 'g' should come before this
number, e.g. libgdbmg1 as package name for the libc6 based
runtime package for libgdbm.
[2] The location ../libc5-compat was introduced in the ldso package. As
ldso is a package on all linus distributions we'll keep it for
compatibility with other distributons even though
/usr/i486-linuxlibc1/lib would be more consistent.
[3] An example for relevant sections of the changelogs for a bugfix
release for both bo and hamm (with the last bo release being
libfoo 1.7.54-6 released on Mon, 16 Jun 1997 and the last hamm
release being libfoo 1.7.54-8 released on Wed, 18 Jun 1997):
-=-=-=-=-=-=-=-=-= bo changelog =-=-=-=-=-=-=-=-=-
libfoo (1.7.54-9) stable; urgency=low
* fixed bug #543547884
-- J.D. Maintainer <jdm@debian.org> Fri, 20 Jun 1997 08:32:03 +0200
libfoo (1.7.54-8) unstable; urgency=low
* hamm release
-- J.D. Maintainer <jdm@debian.org> Fri, 20 Jun 1997 08:32:03 +0200
libfoo (1.7.54-7) unstable; urgency=low
* hamm release
-- J.D. Maintainer <jdm@debian.org> Fri, 20 Jun 1997 08:32:03 +0200
libfoo (1.7.54-6) stable; urgency=low
* added handling of bar.
-- J.D. Maintainer <jdm@debian.org> Mon, 16 Jun 1997 18:45:14 +0200
-=-=-=-=-=-=-=-=-= hamm changelog =-=-=-=-=-=-=-=-=-
libfoo (1.7.54-10) unstable; urgency=low
* fixed bug #543547884
-- J.D. Maintainer <jdm@debian.org> Fri, 20 Jun 1997 08:52:09 +0200
libfoo (1.7.54-9) stable; urgency=low
* bo release
-- J.D. Maintainer <jdm@debian.org> Fri, 20 Jun 1997 08:52:09 +0200
libfoo (1.7.54-8) unstable; urgency=low
* finally made package compliant with those strange policy for hamm
libs.
-- J.D. Maintainer <jdm@debian.org> Wed, 18 Jun 1997 15:34:12 +0200
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--
Helmut Geyer Helmut.Geyer@iwr.uni-heidelberg.de
public PGP key available : finger geyer@saturn.iwr.uni-heidelberg.de
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