o Add support for getting dependencies for a device.

o  dmsetup dependencies <dev>

libdm/ioctl/libdevmapper.c

@@ -75,6 +75,11 @@ int dm_task_get_info(struct dm_task *dmt, struct dm_info *info)
 	return 1;
 }
 
+struct dm_deps *dm_task_get_deps(struct dm_task *dmt)
+{
+	return (struct dm_deps *) (((void *) dmt->dmi) + dmt->dmi->data_start);
+}
+
 int dm_task_set_ro(struct dm_task *dmt)
 {
 	dmt->read_only = 1;
@@ -171,6 +176,8 @@ static void *_add_target(struct target *t, void *out, void *end)
 
 static struct dm_ioctl *_flatten(struct dm_task *dmt)
 {
+	const size_t min_size = 16 * 1024;
+
 	struct dm_ioctl *dmi;
 	struct target *t;
 	size_t len = sizeof(struct dm_ioctl);
@@ -191,6 +198,13 @@ static struct dm_ioctl *_flatten(struct dm_task *dmt)
 	if (dmt->newname)
 		len += strlen(dmt->newname) + 1;
 
+	/*
+	 * Give len a minimum size so that we have space to store
+	 * dependencies or status information.
+	 */
+	if (len < min_size)
+		len = min_size;
+
 	if (!(dmi = malloc(len)))
 		return NULL;
 
@@ -276,6 +290,10 @@ int dm_task_run(struct dm_task *dmt)
 		command = DM_INFO;
 		break;
 
+	case DM_DEVICE_DEPS:
+		command = DM_DEP;
+		break;
+
 	case DM_DEVICE_RENAME:
 		command = DM_RENAME;
 		break;

libdm/libdevmapper.h

@@ -39,6 +39,7 @@ enum {
 	DM_DEVICE_RESUME,
 
 	DM_DEVICE_INFO,
+	DM_DEVICE_DEPS,
 	DM_DEVICE_RENAME,
 
 	DM_DEVICE_VERSION,
@@ -66,10 +67,18 @@ struct dm_info {
 	unsigned int target_count;
 };
 
+struct dm_deps {
+	unsigned int count;
+	dev_t device[0];
+};
+
 int dm_get_library_version(char *version, size_t size);
-int dm_task_get_driver_version(struct dm_task *dmt, char *version, size_t size);
+int dm_task_get_driver_version(struct dm_task *dmt, char *version,
+			       size_t size);
 int dm_task_get_info(struct dm_task *dmt, struct dm_info *dmi);
 
+struct dm_deps *dm_task_get_deps(struct dm_task *dmt);
+
 int dm_task_set_ro(struct dm_task *dmt);
 int dm_task_set_newname(struct dm_task *dmt, const char *newname);
 int dm_task_set_minor(struct dm_task *dmt, int minor);

tools/dmsetup.c

@@ -18,6 +18,7 @@
 #include <errno.h>
 #include <unistd.h>
 #include <getopt.h>
+#include <linux/kdev_t.h>
 
 #define LINE_SIZE 1024
 
@@ -264,6 +265,48 @@ static int _info(int argc, char **argv)
 	return r;
 }
 
+static int _deps(int argc, char **argv)
+{
+	int r = 0, i;
+	struct dm_deps *deps;
+
+	/* remove <dev_name> */
+	struct dm_task *dmt;
+	struct dm_info info;
+
+	if (!(dmt = dm_task_create(DM_DEVICE_DEPS)))
+		return 0;
+
+	if (!dm_task_set_name(dmt, argv[1]))
+		goto out;
+
+	if (!dm_task_run(dmt))
+		goto out;
+
+	if (!(deps = dm_task_get_deps(dmt)))
+		goto out;
+
+	if (!info.exists) {
+		printf("Device does not exist.\n");
+		r = 1;
+		goto out;
+	}
+
+	printf("%d dependencies\t:", deps->count);
+
+	for (i = 0; i < deps->count; i++)
+		printf(" (%d, %d)",
+		       (int) MAJOR(deps->device[i]),
+		       (int) MINOR(deps->device[i]));
+	printf("\n");
+
+	r = 1;
+
+ out:
+	dm_task_destroy(dmt);
+	return r;
+}
+
 
 /*
  * dispatch table
@@ -284,6 +327,7 @@ static struct command _commands[] = {
 	{"resume", "<dev_name>", 1, _resume},
 	{"reload", "<dev_name> <table_file>", 2, _reload},
 	{"info", "<dev_name>", 1, _info},
+	{"dependencies", "<dev_name>", 1, _deps},
 	{"rename", "<dev_name> <new_name>", 2, _rename},
 	{"version", "", 0, _version},
 	{NULL, NULL, 0, NULL}