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(libc.info)NSS Module Names

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The Naming Scheme of the NSS Modules
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The name of each function consist of various parts:

            _nss_SERVICE_FUNCTION

   SERVICE of course corresponds to the name of the module this
function is found in.(1)  The FUNCTION part is derived from the
interface function in the C library itself.  If the user calls the
function `gethostbyname' and the service used is `files' the function

            _nss_files_gethostbyname_r

in the module

            libnss_files.so.2

is used.  You see, what is explained above in not the whole truth.  In
fact the NSS modules only contain reentrant versions of the lookup
functions.  I.e., if the user would call the `gethostbyname_r' function
this also would end in the above function.  For all user interface
functions the C library maps this call to a call to the reentrant
function.  For reentrant functions this is trivial since the interface
is (nearly) the same.  For the non-reentrant version The library keeps
internal buffers which are used to replace the user supplied buffer.

   I.e., the reentrant functions _can_ have counterparts.  No service
module is forced to have functions for all databases and all kinds to
access them.  If a function is not available it is simply treated as if
the function would return `unavail' (Note: Actions in the NSS
configuration).

   The file name `libnss_files.so.2' would be on a Solaris 2 system
`nss_files.so.2'.  This is the difference mentioned above.  Sun's NSS
modules are usable as modules which get indirectly loaded only.

   The NSS modules in the GNU C Library are prepared to be used as
normal libraries themselves.  This is _not_ true at the moment, though.
However,  the organization of the name space in the modules does not
make it impossible like it is for Solaris.  Now you can see why the
modules are still libraries.(2)

   ---------- Footnotes ----------

   (1) Now you might ask why this information is duplicated.  The
answer is that we want to make it possible to link directly with these
shared objects.

   (2) There is a second explanation: we were too lazy to change the
Makefiles to allow the generation of shared objects not starting with
`lib' but don't tell this to anybody.