There is an ongoing effort to limit use of files outside of /usr (or
$prefix on general). Currently all modprobe.d paths are hardcoded to
outside of $prefix. Teach kmod to load modprobe.d from $prefix/lib.

On some distributions /usr/lib and /lib are the same directory because
of a compatibility symlink, and it is possible to craft configuration
files with sideeffects that would behave differently when loaded twice.
However, the override semantic ensures that one 'overrides' the other,
and only one configuration file of the same name is loaded from any of
the search directories.

Signed-off-by: Michal Suchanek <redacted>
---
v2: Fix commit message typo
---
 Makefile.am        | 1 +
 libkmod/libkmod.c  | 3 ++-
 man/Makefile.am    | 9 +++++++--
 man/depmod.d.xml   | 1 +
 man/modprobe.d.xml | 1 +
 tools/depmod.c     | 1 +
 6 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/Makefile.am b/Makefile.am
index 8ba85c91a0f3..7aa5bfa5638d 100644
--- a/Makefile.am
+++ b/Makefile.am

@@ -19,6 +19,7 @@ AM_CPPFLAGS = \
 	-include $(top_builddir)/config.h \
 	-I$(top_srcdir) \
 	-DSYSCONFDIR=\""$(sysconfdir)"\" \
+	-DPREFIX=\""$(prefix)"\" \
 	${zlib_CFLAGS}
 
 AM_CFLAGS = $(OUR_CFLAGS)

diff --git a/libkmod/libkmod.c b/libkmod/libkmod.c
index 2670f9a4611a..13c82b069e84 100644
--- a/libkmod/libkmod.c
+++ b/libkmod/libkmod.c

@@ -65,6 +65,7 @@ static const char *const default_config_paths[] = {
 	SYSCONFDIR "/modprobe.d",
 	"/run/modprobe.d",
 	"/usr/local/lib/modprobe.d",
+	PREFIX "/lib/modprobe.d",
 	"/lib/modprobe.d",
 	NULL
 };

@@ -237,7 +238,7 @@ static char *get_kernel_release(const char *dirname)
  *                to load from user-defined configuration parameters such as
  *                alias, blacklists, commands (install, remove). If NULL
  *                defaults to /etc/modprobe.d, /run/modprobe.d,
- *                /usr/local/lib/modprobe.d and /lib/modprobe.d. Give an empty
+ *                /usr/local/lib/modprobe.d and PREFIX/lib/modprobe.d. Give an empty