[PATCH] modprobe: implement -d DIR flag like the modprobe in kmod

[Adam Joseph]

This patch implements support for the `-d DIR` flag, like kmod has.  When
provided, `DIR` is a directory *beneath which* modprobe will expect to find
$CONFIG_DEFAULT_MODULES_DIR/$(uname -r) (e.g. lib/modules/$(uname -r)).

This is required on nixpkgs-based systems, which do not normally have a
/lib/modules directory.  Instead, a symbolic link at some ephemeral location
in /run points to the proper location.  For example, with mdevd instead of
systemd and the following in mdev.conf:

mdevd-conf = ''
...
$MODALIAS=.* root:root 660 @${pkgs.busybox}/bin/modprobe -d /run/booted-system/kernel-modules -b "$MODALIAS"
...
'';

Compared to setting CONFIG_DEFAULT_MODULES_DIR, a command line flag is
preferable since it allows the same busybox binary to be used both in early
userspace (where the initrd layout often follows FHS and uses /lib/modules) as
well as after switch_root.
---
 modutils/modprobe.c | 24 +++++++++++++++++-------
 1 file changed, 17 insertions(+), 7 deletions(-)

diff --git a/modutils/modprobe.c b/modutils/modprobe.c
index 543f53e99..d3690ebc1 100644
--- a/modutils/modprobe.c
+++ b/modutils/modprobe.c
@@ -114,6 +114,7 @@
 //usage:	" MODULE" IF_FEATURE_CMDLINE_MODULE_OPTIONS(" [SYMBOL=VALUE]...")
 //usage:#define modprobe_full_usage "\n\n"
 //usage:       "	-a	Load multiple MODULEs"
+//usage:     "\n	-d DIR	Use DIR as filesystem root"
 //usage:     "\n	-l	List (MODULE is a pattern)"
 //usage:     "\n	-r	Remove MODULE (stacks) or do autoclean"
 //usage:     "\n	-q	Quiet"
@@ -130,7 +131,7 @@
  * Note2: -b is always accepted, but if !FEATURE_MODPROBE_BLACKLIST,
  * it is a no-op.
  */
-#define MODPROBE_OPTS  "alrDb"
+#define MODPROBE_OPTS  "ad:lrDb"
 /* -a and -D _are_ in fact compatible */
 #define MODPROBE_COMPLEMENTARY "q-v:v-q:l--arD:r--alD:a--lr:D--rl"
 //#define MODPROBE_OPTS  "acd:lnrt:C:b"
@@ -138,20 +139,21 @@
 enum {
 	OPT_INSERT_ALL   = (INSMOD_OPT_UNUSED << 0), /* a */
 	//OPT_DUMP_ONLY  = (INSMOD_OPT_UNUSED << x), /* c */
-	//OPT_DIRNAME    = (INSMOD_OPT_UNUSED << x), /* d */
-	OPT_LIST_ONLY    = (INSMOD_OPT_UNUSED << 1), /* l */
+	OPT_DIRNAME      = (INSMOD_OPT_UNUSED << 1), /* d */
+	OPT_LIST_ONLY    = (INSMOD_OPT_UNUSED << 2), /* l */
 	//OPT_SHOW_ONLY  = (INSMOD_OPT_UNUSED << x), /* n */
-	OPT_REMOVE       = (INSMOD_OPT_UNUSED << 2), /* r */
+	OPT_REMOVE       = (INSMOD_OPT_UNUSED << 3), /* r */
 	//OPT_RESTRICT   = (INSMOD_OPT_UNUSED << x), /* t */
 	//OPT_VERONLY    = (INSMOD_OPT_UNUSED << x), /* V */
 	//OPT_CONFIGFILE = (INSMOD_OPT_UNUSED << x), /* C */
-	OPT_SHOW_DEPS    = (INSMOD_OPT_UNUSED << 3), /* D */
-	OPT_BLACKLIST    = (INSMOD_OPT_UNUSED << 4) * ENABLE_FEATURE_MODPROBE_BLACKLIST,
+	OPT_SHOW_DEPS    = (INSMOD_OPT_UNUSED << 4), /* D */
+	OPT_BLACKLIST    = (INSMOD_OPT_UNUSED << 5) * ENABLE_FEATURE_MODPROBE_BLACKLIST,
 };
 #if ENABLE_LONG_OPTS
 static const char modprobe_longopts[] ALIGN1 =
 	/* nobody asked for long opts (yet) */
 	// "all\0"          No_argument "a"
+	// "dirname\0"      required_argument "d"
 	// "list\0"         No_argument "l"
 	// "remove\0"       No_argument "r"
 	// "quiet\0"        No_argument "q"
@@ -559,17 +561,25 @@ int modprobe_main(int argc UNUSED_PARAM, char **argv)
 	int rc;
 	unsigned opt;
 	struct module_entry *me;
+	const char* dirname;
 
 	INIT_G();
 
 	opt = getopt32long(argv, "^" INSMOD_OPTS MODPROBE_OPTS "\0" MODPROBE_COMPLEMENTARY,
 			modprobe_longopts
 			INSMOD_ARGS
+			, &dirname
 	);
 	argv += optind;
 
 	/* Goto modules location */
-	xchdir(CONFIG_DEFAULT_MODULES_DIR);
+	if (opt & OPT_DIRNAME) {
+		xchdir(dirname);
+		xchdir(&CONFIG_DEFAULT_MODULES_DIR[1]);
+	} else {
+		xchdir(CONFIG_DEFAULT_MODULES_DIR);
+	}
+
 	uname(&G.uts);
 	xchdir(G.uts.release);
 
-- 
2.44.0