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| <h4 class="subsection">28.4.1 Adding another Service to NSS</h4> |
| |
| <p>The sources for a new service need not (and should not) be part of the |
| GNU C Library itself. The developer retains complete control over the |
| sources and its development. The links between the C library and the |
| new service module consists solely of the interface functions. |
| |
| <p>Each module is designed following a specific interface specification. |
| For now the version is 2 (the interface in version 1 was not adequate) |
| and this manifests in the version number of the shared library object of |
| the NSS modules: they have the extension <code>.2</code>. If the interface |
| changes again in an incompatible way, this number will be increased. |
| Modules using the old interface will still be usable. |
| |
| <p>Developers of a new service will have to make sure that their module is |
| created using the correct interface number. This means the file itself |
| must have the correct name and on ELF systems the <dfn>soname</dfn> (Shared |
| Object Name) must also have this number. Building a module from a bunch |
| of object files on an ELF system using GNU CC could be done like this: |
| |
| <pre class="smallexample"> gcc -shared -o libnss_NAME.so.2 -Wl,-soname,libnss_NAME.so.2 OBJECTS |
| </pre> |
| <p class="noindent"><a href="../gcc/Link-Options.html#Link-Options">Options for Linking</a>, to learn |
| more about this command line. |
| |
| <p>To use the new module the library must be able to find it. This can be |
| achieved by using options for the dynamic linker so that it will search |
| the directory where the binary is placed. For an ELF system this could be |
| done by adding the wanted directory to the value of |
| <code>LD_LIBRARY_PATH</code>. |
| |
| <p>But this is not always possible since some programs (those which run |
| under IDs which do not belong to the user) ignore this variable. |
| Therefore the stable version of the module should be placed into a |
| directory which is searched by the dynamic linker. Normally this should |
| be the directory <samp><span class="file">$prefix/lib</span></samp>, where <samp><span class="file">$prefix</span></samp> corresponds to |
| the value given to configure using the <code>--prefix</code> option. But be |
| careful: this should only be done if it is clear the module does not |
| cause any harm. System administrators should be careful. |
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