(libc.info.gz) Adding another Service to NSS

(libc.info.gz) NSS Module Function Internals
 
 29.4.1 Adding another Service to NSS
 ------------------------------------
 
 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.
 
    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 '.2'.  If the interface changes
 again in an incompatible way, this number will be increased.  Modules
 using the old interface will still be usable.
 
    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 "soname"
 (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:
 
      gcc -shared -o libnss_NAME.so.2 -Wl,-soname,libnss_NAME.so.2 OBJECTS
 
  Options for Linking (gcc)Link Options, to learn more about this
 command line.
 
    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
 'LD_LIBRARY_PATH'.
 
    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 '$prefix/lib', where '$prefix' corresponds to the value
 given to configure using the '--prefix' 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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