libkmod: tools: Introduce 'module alternative' directory (was: module fallback)

Makefile.am

@@ -32,6 +32,8 @@ AM_CPPFLAGS = \
 	-DSYSCONFDIR=\""$(sysconfdir)"\" \
 	-DDISTCONFDIR=\""$(distconfdir)"\" \
 	-DMODULE_DIRECTORY=\""$(module_directory)"\" \
+	-DENABLE_ALTERNATIVE_DIR=\""$(enable_alternative_dir)
+	-DMODULE_ALTERNATIVE_DIRECTORY=\""$(module_alternative_directory)"\" \
 	${zlib_CFLAGS}
 
 AM_CFLAGS = $(OUR_CFLAGS)
@@ -198,7 +200,7 @@ MODULE_PLAYGROUND = testsuite/module-playground
 BUILD_MODULES = $(AM_V_GEN) $(top_srcdir)/scripts/setup-modules.sh $(top_srcdir) $(top_builddir) $(MODULE_PLAYGROUND)
 ROOTFS = testsuite/rootfs
 ROOTFS_PRISTINE = $(top_srcdir)/testsuite/rootfs-pristine
-CREATE_ROOTFS = $(AM_V_GEN) $(top_srcdir)/scripts/setup-rootfs.sh $(ROOTFS_PRISTINE) $(ROOTFS) $(MODULE_PLAYGROUND) $(top_builddir)/config.h $(sysconfdir) $(module_directory)
+CREATE_ROOTFS = $(AM_V_GEN) $(top_srcdir)/scripts/setup-rootfs.sh $(ROOTFS_PRISTINE) $(ROOTFS) $(MODULE_PLAYGROUND) $(top_builddir)/config.h $(sysconfdir) $(module_directory) $(module_alternative_directory)
 
 build-module-playground:
 	$(BUILD_MODULES)

configure.ac

@@ -89,8 +89,16 @@ AC_ARG_WITH([module_directory],
         [], [with_module_directory=/lib/modules])
 AC_SUBST([module_directory], [$with_module_directory])
 
+AC_ARG_ENABLE([enable_alternative_dir],
+	AS_HELP_STRING([--enable-alternative-dir], [enable alternative module directory @<:@default=disabled@:>@]),
+	[], [enable_alternative_dir=no])
+AC_ARG_WITH([module_alternative_directory],
+        AS_HELP_STRING([--with-module-alternative_directory=DIR], [alternative directory in which to look for kernel modules @<:@default=/run/modules@:>@]),
+        [], [with_module_alternative_directory=/run/modules])
+AC_SUBST([module_alternative_directory], [$with_module_alternative_directory])
+
 # Check all directory arguments for consistency.
-for ac_var in	distconfdir module_directory
+for ac_var in	distconfdir module_directory module_alternative_directory
 do
   eval ac_val=\$$ac_var
   # Remove trailing slashes.
@@ -335,26 +343,28 @@ AC_MSG_RESULT([
 	$PACKAGE $VERSION
 	=======
 
-	module_directory:	${module_directory}
-	prefix:			${prefix}
-	sysconfdir:		${sysconfdir}
-	distconfdir:		${distconfdir}
-	libdir:			${libdir}
-	includedir:		${includedir}
-	bindir:			${bindir}
-	Bash completions dir:   ${with_bashcompletiondir}
-
-	compiler:		${CC}
-	cflags:			${with_cflags} ${CFLAGS}
-	ldflags:		${with_ldflags} ${LDFLAGS}
-
-	tools:			${enable_tools}
-	logging:		${enable_logging}
-	compression:		zstd=${with_zstd}  xz=${with_xz}  zlib=${with_zlib}
-	debug:			${enable_debug}
-	coverage:		${enable_coverage}
-	doc:			${enable_gtk_doc}
-	man:			${enable_manpages}
-
-	features:               ${with_features}
+	module_directory:		${module_directory}
+	enable_alternative_dir:		${enable_alternative_dir}
+	module_alternative_directory:	${module_alternative_directory}
+	prefix:				${prefix}
+	sysconfdir:			${sysconfdir}
+	distconfdir:			${distconfdir}
+	libdir:				${libdir}
+	includedir:			${includedir}
+	bindir:				${bindir}
+	Bash completions dir:   	${with_bashcompletiondir}
+
+	compiler:			${CC}
+	cflags:				${with_cflags} ${CFLAGS}
+	ldflags:			${with_ldflags} ${LDFLAGS}
+
+	tools:				${enable_tools}
+	logging:			${enable_logging}
+	compression:			zstd=${with_zstd}  xz=${with_xz}  zlib=${with_zlib}
+	debug:				${enable_debug}
+	coverage:			${enable_coverage}
+	doc:				${enable_gtk_doc}
+	man:				${enable_manpages}
+
+	features:               	${with_features}
 ])

man/Makefile.am

@@ -18,6 +18,7 @@ define generate_manpage
 	sed -e 's|@SYSCONFDIR@|$(sysconfdir)|g' | \
 	sed -e 's|@DISTCONFDIR@|$(distconfdir)|g' | \
 	sed -e 's|@MODULE_DIRECTORY@|$(module_directory)|g' | \
+	sed -e 's|@MODULE_ALTERNATIVE_DIRECTORY@|$(module_alternative_directory)|g' | \
 	$(SCDOC) > $@
 endef
 

man/insmod.8.scd

@@ -18,6 +18,13 @@ Only the most general of error messages are reported: as the work of trying to
 link the module is now done inside the kernel, the *dmesg*(1) usually gives more
 information about errors.
 
+*insmod* will look by default at modules stored in @MODULE_DIRECTORY@, but if
+the folder is missing or the module is not found and kmod is compiled with
+@enable-alternative-dir=true@, it will automatically look at the fallback
+directory @MODULE_ALTERNATIVE_DIRECTORY@.
+In that case, this program will only fail if the provided module is not found in
+both directories.
+
 # OPTIONS
 
 *-f*, *--force*

man/lsmod.8.scd

@@ -13,6 +13,9 @@ lsmod - Show the status of modules in the Linux Kernel
 *lsmod* is a trivial program which nicely formats the contents of the
 _/proc/modules_, showing what kernel modules are currently loaded.
 
+*lsmod* will look by default at modules stored in @MODULE_DIRECTORY@, but if
+the folder is missing , it will automatically look at the fallback directory @MODULE_ALTERNATIVE_DIRECTORY@.
+
 # OPTIONS
 
 *-s*, *--syslog*

man/modinfo.8.scd

@@ -15,9 +15,19 @@ modinfo - Show information about a Linux Kernel module
 # DESCRIPTION
 
 *modinfo* extracts information from the Linux Kernel modules given on the
-command line. If the module name is not a filename, then the @MODULE_DIRECTORY@/
-_version_ directory is searched, as is also done by *modprobe*(8) when loading
-kernel modules.
+command line.
+
+*modinfo* will search by default for modules stored in @MODULE_DIRECTORY@, but
+if the folder is missing or the module is not found and kmod is compiled with
+@enable-alternative-dir=true@, it will automatically look at the fallback
+directory @MODULE_ALTERNATIVE_DIRECTORY@.
+In that case, this program will only fail if the provided module is not found in
+both directories.
+
+If the module name is not a filename, then the @MODULE_DIRECTORY@/
+_version_ directory is searched first, and then if enabled
+@MODULE_ALTERNATIVE_DIRECTORY@/_version_, as is also done by *modprobe*(8) when
+loading kernel modules.
 
 *modinfo* by default lists each attribute of the module in form _fieldname_ :
 _value_, for easy reading. The filename is listed the same way (although it's

man/modprobe.8.scd

@@ -44,6 +44,30 @@ is relative, it must explicitly start with "./". Note that this may fail when
 using a path to a module with dependencies not matching the installed *depmod*
 database.
 
+*modprobe* will search by default for modules stored in @MODULE_DIRECTORY@, but
+if the folder is missing or the module is not found and kmod is compiled with
+@enable-alternative-dir=true@, it will automatically look at the fallback
+directory @MODULE_ALTERNATIVE_DIRECTORY@.
+In that case, this program will only fail if the provided module is not found in
+both directories.
+
+The rationale for @MODULE_ALTERNATIVE_DIRECTORY@ is that this folder could be
+used to reference pre-build or distro-provided default modules, and leave
+@MODULE_DIRECTORY@ to point custom locally generated modules. In this way, the
+first lookup always happens in @MODULE_DIRECTORY@ and will always reference the
+local modules, but if for some reason some module is missing,
+@MODULE_ALTERNATIVE_DIRECTORY@ could be used as fallback as source of default
+standard modules.
+
+Another specific use case for this is with UKIs (Unified Kernel Image).
+In this scenario, there is the possibility of not keeping two copies of the
+kernel modules (one for initramfs and not for rootfs), but instead copy the ones
+in initramfs to tmpfs, e.g. in /run/modules. Note that modules are not directly
+copied in rootfs because it might also be read-only mounted.
+This copy is feasible because an UKI ships kernel and initramfs together, so
+there is no need to locally build anything, avoiding kernel-initramfs version
+mismatches.
+
 # OPTIONS
 
 *-a*, *--all*

man/rmmod.8.scd

@@ -15,6 +15,13 @@ kernel (when module unloading support is provided). Most users will want to use
 *modprobe*(8) with the *-r* option instead since it removes unused dependent
 modules as well.
 
+*rmmod* will look by default at modules stored in @MODULE_DIRECTORY@, but if
+the folder is missing or the module is not found and kmod is compiled with
+@enable-alternative-dir=true@, it will automatically look at the fallback
+directory @MODULE_ALTERNATIVE_DIRECTORY@.
+In that case, this program will only fail if the provided module is not found in
+both directories.
+
 When a list of modules is provided, the program will process them one at a time.
 If a module is not found, *rmmod* will immediately exit with an error code.
 Should the module removal fail, the program will log an error AND continue with

meson.build

@@ -193,6 +193,9 @@ datadir = prefixdir / get_option('datadir')
 
 distconfdir = get_option('distconfdir')
 moduledir = get_option('moduledir')
+enablealternativedir = get_option('enable-alternative-dir')
+modulealternativedir = get_option('modulealternativedir')
+cdata.set10('ENABLE_ALTERNATIVE_DIR', enablealternativedir)
 
 bashcompletiondir = get_option('bashcompletiondir')
 fishcompletiondir = get_option('fishcompletiondir')
@@ -204,6 +207,7 @@ _customdirs = [
   # The defaults are hard-coded due to historical reasons
   ['distconfdir', prefixdir / 'lib',  'DISTCONFDIR'],
   ['moduledir',   '/lib/modules',     'MODULE_DIRECTORY'],
+  ['modulealternativedir', '/run/modules', 'MODULE_ALTERNATIVE_DIRECTORY'],
 ]
 
 foreach tuple : _customdirs
@@ -472,6 +476,7 @@ _kmod_variables = [
   'sysconfdir=' + sysconfdir,
   'distconfdir=' + distconfdir,
   'module_directory=' + moduledir,
+  'module_alternative_directory=' + modulealternativedir,
 ]
 
 # Don't (space) escape variables with space-separated lists, for consistency
@@ -565,6 +570,7 @@ summary({
 summary({
   'distconfdir' : distconfdir,
   'moduledir'   : moduledir,
+  'modulealternativedir'   : modulealternativedir,
 }, section : 'Kmod specific')
 
 summary({
@@ -574,13 +580,14 @@ summary({
 }, section : 'Shell completions')
 
 summary({
-  'tools'           : get_option('tools'),
-  'logging'         : get_option('logging'),
-  'debug-messages'  : get_option('debug-messages'),
-  'build-tests'     : get_option('build-tests'),
-  'manpages'        : get_option('manpages'),
-  'docs'            : get_option('docs'),
-  'dlopen'          : get_option('dlopen'),
+  'tools'                       : get_option('tools'),
+  'logging'                     : get_option('logging'),
+  'debug-messages'              : get_option('debug-messages'),
+  'build-tests'                 : get_option('build-tests'),
+  'enable-alternative-dir'      : get_option('enable-alternative-dir'),
+  'manpages'                    : get_option('manpages'),
+  'docs'                        : get_option('docs'),
+  'dlopen'                      : get_option('dlopen'),
 }, section : 'Options')
 
 summary({

meson_options.txt

@@ -12,6 +12,19 @@ option(
   description : 'Directory to look for kernel modules. Default: /lib/modules',
 )
 
+option(
+  'enable-alternative-dir',
+  type : 'boolean',
+  value : false,
+  description : 'Always use a fallback alternative directory to look for kernel modules. Default: false',
+)
+
+option(
+  'modulealternativedir',
+  type : 'string',
+  description : 'Alternative directory to look for kernel modules, if enable-alternative-dir is true. Otherwise unused. Default: /run/modules',
+)
+
 option(
   'bashcompletiondir',
   type : 'string',

scripts/setup-rootfs.sh

@@ -8,6 +8,7 @@ MODULE_PLAYGROUND=$3
 CONFIG_H=$4
 SYSCONFDIR=$5
 MODULE_DIRECTORY=$6
+MODULE_ALTERNATIVE_DIRECTORY=$7
 
 # create rootfs from rootfs-pristine
 

testsuite/meson.build

@@ -28,6 +28,7 @@ create_rootfs = custom_target(
     meson.project_build_root() / 'config.h',
     sysconfdir,
     moduledir,
+    modulealternativedir,
   ],
   output : 'stamp-rootfs',
   console : true,

testsuite/rootfs-pristine/test-modinfo/builtin/run/modules/6.11.0

@@ -0,0 +1 @@
+../../../external/lib/modules/4.4.4

testsuite/rootfs-pristine/test-modinfo/external/run/modules/4.4.4

@@ -0,0 +1 @@
+../../../builtin/lib/modules/6.11.0

testsuite/test-modinfo.c

@@ -124,4 +124,49 @@ DEFINE_TEST(test_modinfo_builtin,
 		.out = TESTSUITE_ROOTFS "test-modinfo/correct-builtin.txt",
 	});
 
+static noreturn int test_modinfo_alternative(const struct test *t)
+{
+	const char *const args[] = {
+		// clang-format off
+		progname,
+		"-F", "filename",
+		"mod-simple",
+		NULL,
+		// clang-format on
+	};
+	test_spawn_prog(progname, args);
+	exit(EXIT_FAILURE);
+}
+DEFINE_TEST(test_modinfo_alternative,
+	.description = "check if modinfo finds module in alternative directory",
+	.config = {
+		[TC_ROOTFS] = TESTSUITE_ROOTFS "test-modinfo/builtin",
+		[TC_UNAME_R] = "6.11.0",
+	},
+	.output = {
+		.out = TESTSUITE_ROOTFS "test-modinfo/correct-external.txt",
+	});
+
+static noreturn int test_modinfo_alternative_inv(const struct test *t)
+{
+	const char *const args[] = {
+		// clang-format off
+		progname,
+		"intel_uncore",
+		NULL,
+		// clang-format on
+	};
+	test_spawn_prog(progname, args);
+	exit(EXIT_FAILURE);
+}
+DEFINE_TEST(test_modinfo_alternative_inv,
+	.description = "check if modinfo finds module in alternative directory",
+	.config = {
+		[TC_ROOTFS] = TESTSUITE_ROOTFS "test-modinfo/external",
+		[TC_UNAME_R] = "4.4.4",
+	},
+	.output = {
+		.out = TESTSUITE_ROOTFS "test-modinfo/correct-builtin.txt",
+	});
+
 TESTSUITE_MAIN();