Reminder:

When ABI is stable, an application build with version N of a library will works with version N+1. This allow update without need to rebuild a lot of packages.

For example, when an application use the MySQL client, it is linked with libmysqlclient.so. In reality, it will use the libmysqlclient.so.16 library. This version "16" (soname) will be the same for all the MySQL 5.1 libraries. (MySQL 5.0 provides libmysqlclient.so.15). ABI stability is guaranteed. RPM implement this check using dependencies on the versionned name of the used libraries.

$ rpm -q --provides mysql-libs
libmysqlclient.so.16()(64bit)  
libmysqlclient_r.so.16()(64bit)
...
$ rpm -q --requires mysql++
libc.so.6()(64bit)  
libgcc_s.so.1()(64bit)  
libm.so.6()(64bit)  
libmysqlclient_r.so.16()(64bit)  
libmysqlpp.so.3()(64bit)  
libpthread.so.0()(64bit)  
...

Normally, it's the developer job to ensure, upstream, this stability. When a change is necessary the library version must change (no link with the sources version). The package maintainer must rebuild all applications which use it or provide a compatibility librayry.

Of course, this is a good practice, for a packager, to check this stability before pushing an update in the distribution.

Sample:

For the update of new version 3.1.0 of mysql++, I've done this check and write this blog's entry to keep a reminder on the used method, and share it with others.

I used a simple and free tool : ABI compliance checker and the trivial test of running a simple application.

With  version 3.0.9

Build the examples provided (without the version check provided)

$ su -lc "yum install mysql++-devel"
$ cp -r /usr/share/doc/mysql++-devel-3.0.9/examples /tmp/ex309
$ cd /tmp/ex309
$ vi resetdb.cpp # delete the return 1 after the version check
$ make

Install the tool and run the analysis for version 3.0.9

$ wget http://ispras.linux-foundation.org/images/6/6e/Abi-compliance-checker-1.17.2.tar.gz
$ tar xzf Abi-compliance-checker-1.17.2.tar.gz
$ cd abi-compliance-checker-1.17.2
$ ./abi-compliance-checker.pl -d
$ mv lib_ver.xml my309.xml
$ gedit mysql++309.xml
$ abi-compliance-checker -l mysql++ -dump_abi mysql++309.xml

mysql++309.xml file, describing the library, is quite simple:

<?xml version="1.0" encoding="UTF-8"?>
<descriptor>
<version>
    3.0.9
</version>
<headers>
    /usr/include/mysql++/
</headers>
<libs>
    /usr/lib64/libmysqlpp.so
</libs>
<include_paths>
    /usr/include/mysql
</include_paths>
...

The result file will be used later.

With version 3.1.0

update the library. Examples must still works.

$ su -lc "rpm -Uvh mysql++*3.1.0*"
$ cd /tmp/ex309
$ ./simple1 -u toto -p secret
We have:
    Nuerenberger Bratwurst
    Pickle Relish
    Hot Mustard
    Hotdog Buns
    Hot Dogs
$ ./cpool -u toto -p secret
Segmentation fault (core dumped)

It seems there is a problem.

Run the analysis

$ cp mysql++309.xml mysql++310.xml
$ gedit mysql++310.xml
$ abi-compliance-checker -l mysql++ -dump_abi mysql++310.xml

Run comparison of the 2 results.

$ ./abi-compliance-checker.pl -l mysql++ \
   -d1 abi_dumps/mysql++/mysql++_3.0.9.abi.tar.gz \
   -d2 abi_dumps/mysql++/mysql++_3.1.0.abi.tar.gz
$ firefox file:$PWD/compat_reports/mysql++/3.0.9_to_3.1.0/abi_compat_report.html

Here is the report : ABI compliance report for the library mysql++ from version 3.0.9 to 3.1.0 on x86_64

In the case, it confirm the ABI breakage between the 2 versions. So, of course, the update in the stable repository will not happen.

Outcome:

Of course, this issue must be reported to the upstream developers and to other package maintainers

When I start maintaining this package (version 2.x), the library was even not versionned. So I have to work with developers to include this feature. Now I need to convince them to respect the pratices.