What drives RPM Provides for shared libraries?

[Nicholas Miell]

On 12/21/2010 07:42 PM, Matt McCutchen wrote:
> On Tue, 2010-12-21 at 22:10 -0500, Tom Lane wrote:
>> I'm fooling around with trying to update mysql from 5.1.x to 5.5.x.
>> One of the things that's happened in that transition is that they've
>> dropped the separate "libmysqlclient_r.so" library --- presumably
>> everything in regular "libmysqlclient.so" is now thread-safe.
>> Upstream's idea of maintaining ABI compatibility is to provide
>> symlinks, libmysqlclient_r.so.16.0.0 -> libmysqlclient.so.16.0.0
>> etc.  I find that that only sort of works --- RPM fails to generate
>> the --provides entries that it used to.  So for example I have
>> this with the old RPMs:
>>
>> $ rpm -qp mysql-libs-5.1.52-1.fc13.x86_64.rpm --provides
>> config(mysql-libs) = 5.1.52-1.fc13
>> libmysqlclient.so.16()(64bit)  
>> libmysqlclient.so.16(libmysqlclient_16)(64bit)  
>> libmysqlclient_r.so.16()(64bit)  
>> libmysqlclient_r.so.16(libmysqlclient_16)(64bit)  
>> mysql-libs = 5.1.52-1.fc13
>> mysql-libs(x86-64) = 5.1.52-1.fc13
>>
>> but the closest I've been able to get with the new ones is
>>
>> $ rpm -qp mysql-libs-5.5.8-1.fc13.x86_64.rpm --provides
>> config(mysql-libs) = 5.5.8-1.fc13
>> libmysqlclient.so.16()(64bit)  
>> libmysqlclient.so.16(libmysqlclient_16)(64bit)  
>> mysql-libs = 5.5.8-1.fc13
>> mysql-libs(x86-64) = 5.5.8-1.fc13
>>
>> I thought for a bit that RPM was ignoring symlinks for this purpose, but
>> even copying instead of symlinking the library didn't get me a second
>> set of provides items.  What drives those decisions?
> 
> I guess RPM is using the SONAME embedded in the library, which you can
> see with "readelf -d".  Assuming that ld.so is happy to satisfy a NEEDED
> entry for libmysqlclient_r.so.16 by opening a file with that name and
> getting a library with SONAME libmysqlclient.so.16, it seems that rpm
> should add the Provides based on the file name.
> 

ld.so isn't happy with that (lookups aren't based on filenames, so
symlinks won't do anything and it will never find the library).

You need to create an empty shared library with the
libmysqlclient_r.so.16 SONAME that has a DT_AUXILIARY entry for
libmysqlclient.so.16.