Implement lt_dlopening of only preloaded modules.

* libltdl/m4/ltdl.m4 (LTDL_INIT): Check for a libltdl that
provides lt_dladvise_preopen when deciding if installed libltdl
is 'new enough'.
* libltdl/libltdl/lt__private.h (lt__advise): Add a new
is_preload flag.
* libltdl/ltdl.c (lt_dladvise_preload): New api call to set it.
(try_dlopen): If it is set, and the search of preloaded modules
didn't return a match, don't bother searching the filesystem.
* libltdl/ltdl.h (lt_dladvise_preload): Declare it.
* doc/libtool.texi (Libltdl Interface): Document it.
* tests/lt_dladvise.at: Test it (and incidentally add some test
coverage for `libtool -dlpreopen').
* NEWS: Announce it.

1 files changed, 7 insertions, 0 deletions

diff --git a/doc/libtool.texi b/doc/libtool.texi
index b09cc2ae..7b6b3f57 100644
--- a/doc/libtool.texi
+++ b/doc/libtool.texi
@@ -3816,6 +3816,13 @@ On failure, @code{lt_dladvise_resident} returns non-zero and sets an error
 message that can be retrieved with @code{lt_dlerror}.
 @end deftypefun
 
+@deftypefun int lt_dladvise_preload (lt_dladvise *@var{advise})
+Set the @code{preload} hint on @var{advise}.  Passing an @var{advise}
+parameter to @code{lt_dlopenadvise} with this hint set causes it to
+load only preloaded modules, so that if a suitable preloaded module is
+not found, @code{lt_dlopenadvise} will return @code{NULL}.
+@end deftypefun
+
 @deftypefun int lt_dlclose (lt_dlhandle @var{handle})
 Decrement the reference count on the module @var{handle}.
 If it drops to zero and no other module depends on this module,