autoload i2c-dev module when needed

["Michal Minář" <miminar-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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Hello,

we've got following request (viz [1]):

i2cdetect requires the i2c-dev module be loaded so the appropriate
/dev entries are created. This is not done automatically, so when
i2cdetect is initially run it gives the false impression that no
buses/devices exist:

# i2cdetect -l
# modprobe i2c-dev
# i2cdetect -l
i2c-0	i2c       	i915 gmbus ssc                  	I2C adapter
i2c-1	i2c       	i915 gmbus vga                  	I2C adapter
i2c-2	i2c       	i915 gmbus panel                	I2C adapter
i2c-3	i2c       	i915 gmbus dpc                  	I2C adapter
i2c-4	i2c       	i915 gmbus dpb                  	I2C adapter
i2c-5	i2c       	i915 gmbus dpd                  	I2C adapter
i2c-6	i2c       	DPDDC-C                         	I2C adapter
i2c-7	i2c       	DPDDC-D                         	I2C adapter


Attached is a patch that autoloads i2c-dev module when neccessary. If
you like it and have commit rights, push it please instead of me. If
you don't like it, don't hold back and tell me.

Best regards,
Michal Minar

[1] https://bugzilla.redhat.com/show_bug.cgi?id=913203
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Index: i2c-tools-3.1.0/tools/i2cbusses.c
===================================================================
--- i2c-tools-3.1.0.orig/tools/i2cbusses.c
+++ i2c-tools-3.1.0/tools/i2cbusses.c
@@ -37,9 +37,15 @@
 #include <dirent.h>
 #include <fcntl.h>
 #include <errno.h>
+#ifdef USE_LIBKMOD
+	#include <libkmod.h>
+#endif
 #include "i2cbusses.h"
 #include <linux/i2c-dev.h>
 
+#define BUFLEN 512
+#define I2C_DEV_MOD_NAME "i2c_dev"
+
 enum adt { adt_dummy, adt_isa, adt_i2c, adt_smbus, adt_unknown };
 
 struct adap_type {
@@ -60,6 +66,70 @@ static struct adap_type adap_types[5] =
 	  .algo		= "N/A", },
 };
 
+/**
+ * Try to load i2c_dev kernel mode. Do nothing, if module is already loaded.
+ * Returns 1 on success, 0 otherwise.
+ */
+static int try_load_i2c_dev_mod(void) {
+	int err = 0, loaded = 0;
+	char errbuf[BUFLEN] = { 0 };
+#ifdef USE_LIBKMOD
+	int flags = 0;
+	struct kmod_ctx *ctx;
+	struct kmod_list *l, *list = NULL;
+
+	ctx = kmod_new(NULL, NULL);
+	if (!ctx) {
+		snprintf(errbuf, BUFLEN, "kmod_new() failed!");
+		goto done;
+	}
+	if (kmod_module_new_from_lookup(ctx, I2C_DEV_MOD_NAME, &list) < 0 || list == NULL) {
+		snprintf(errbuf, BUFLEN, I2C_DEV_MOD_NAME " module lookup failed");
+		goto ctx_unref;
+	}
+
+	flags |= KMOD_PROBE_APPLY_BLACKLIST_ALIAS_ONLY;
+	kmod_list_foreach(l, list) {
+		struct kmod_module *mod = kmod_module_get_module(l);
+		err = kmod_module_probe_insert_module(mod, flags, NULL, NULL, NULL, NULL);
+		if (err == -ENOENT) {
+			snprintf(errbuf, BUFLEN,
+					"unknown symbol in module \"%s\", or unknown parameter (see dmesg)",
+					kmod_module_get_name(mod));
+		} else if (err < 0) {
+			snprintf(errbuf, BUFLEN, "(module %s): %s",
+					kmod_module_get_name(mod), strerror(-err));
+		} else {
+			kmod_module_unref(mod);
+			++loaded;
+			break;
+		}
+		kmod_module_unref(mod);
+	}
+
+list_unref:
+	kmod_module_unref_list(list);
+ctx_unref:
+	kmod_unref(ctx);
+#else
+	err = system("modprobe " I2C_DEV_MOD_NAME);
+	if (err < 0) {
+		snprintf(errbuf, BUFLEN, "failed to execute modprobe command");
+	} else if (err > 0) {
+		snprintf(errbuf, BUFLEN, "modprobe command exited with code %d",
+				WEXITSTATUS(err));
+	} else {
+		++loaded;
+		goto done;
+	}
+#endif
+	if (errbuf[0])
+		fprintf(stderr, "Failed to load required " I2C_DEV_MOD_NAME
+			   	" kernel module: %s\n", errbuf);
+done:
+	return loaded;
+}
+
 static enum adt i2c_get_funcs(int i2cbus)
 {
 	unsigned long funcs;
@@ -206,8 +276,12 @@ struct i2c_adap *gather_i2c_busses(void)
 	   i2c-dev and what we really care about are the i2c-dev numbers.
 	   Unfortunately the names are harder to get in i2c-dev */
 	strcat(sysfs, "/class/i2c-dev");
-	if(!(dir = opendir(sysfs)))
-		goto done;
+	if(!(dir = opendir(sysfs))) {
+		if (!try_load_i2c_dev_mod())
+			goto done;
+		if ((!(dir = opendir(sysfs))))
+			goto done;
+	}
 	/* go through the busses */
 	while ((de = readdir(dir)) != NULL) {
 		if (!strcmp(de->d_name, "."))
Index: i2c-tools-3.1.0/tools/Module.mk
===================================================================
--- i2c-tools-3.1.0.orig/tools/Module.mk
+++ i2c-tools-3.1.0/tools/Module.mk
@@ -15,6 +15,11 @@ TOOLS_CFLAGS	:= -Wstrict-prototypes -Wsh
 
 TOOLS_TARGETS	:= i2cdetect i2cdump i2cset i2cget
 
+ifeq ($(shell pkg-config --exists libkmod && echo 1), 1)
+    TOOLS_CFLAGS  += $(shell pkg-config --cflags libkmod) -DUSE_LIBKMOD
+    LDFLAGS += $(shell pkg-config --libs libkmod)
+endif
+
 #
 # Programs
 #

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