target: make target db location configurable

This commit adds the read-write attribute "dbroot",
in the top-level CONFIGFS (core) target directory,
normally /sys/kernel/config/target. This attribute
defaults to "/var/target" but can be changed by
writing a new pathname string to it. Changing this
attribute is only allowed when no fabric drivers
are loaded and the supplied value specifies an
existing directory.

Target modules that care about the target database
root directory will be modified to use this
attribute in a future commit.

Signed-off-by: Lee Duncan <[e-mail]>
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/target/target_core_configfs.c

···
 
 CONFIGFS_ATTR_RO(target_core_item_, version);
 
+char db_root[DB_ROOT_LEN] = DB_ROOT_DEFAULT;
+static char db_root_stage[DB_ROOT_LEN];
+
+static ssize_t target_core_item_dbroot_show(struct config_item *item,
+					    char *page)
+{
+	return sprintf(page, "%s\n", db_root);
+}
+
+static ssize_t target_core_item_dbroot_store(struct config_item *item,
+					const char *page, size_t count)
+{
+	ssize_t read_bytes;
+	struct file *fp;
+
+	mutex_lock(&g_tf_lock);
+	if (!list_empty(&g_tf_list)) {
+		mutex_unlock(&g_tf_lock);
+		pr_err("db_root: cannot be changed: target drivers registered");
+		return -EINVAL;
+	}
+
+	if (count > (DB_ROOT_LEN - 1)) {
+		mutex_unlock(&g_tf_lock);
+		pr_err("db_root: count %d exceeds DB_ROOT_LEN-1: %u\n",
+		       (int)count, DB_ROOT_LEN - 1);
+		return -EINVAL;
+	}
+
+	read_bytes = snprintf(db_root_stage, DB_ROOT_LEN, "%s", page);
+	if (!read_bytes) {
+		mutex_unlock(&g_tf_lock);
+		return -EINVAL;
+	}
+	if (db_root_stage[read_bytes - 1] == '\n')
+		db_root_stage[read_bytes - 1] = '\0';
+
+	/* validate new db root before accepting it */
+	fp = filp_open(db_root_stage, O_RDONLY, 0);
+	if (IS_ERR(fp)) {
+		mutex_unlock(&g_tf_lock);
+		pr_err("db_root: cannot open: %s\n", db_root_stage);
+		return -EINVAL;
+	}
+	if (!S_ISDIR(fp->f_inode->i_mode)) {
+		filp_close(fp, 0);
+		mutex_unlock(&g_tf_lock);
+		pr_err("db_root: not a directory: %s\n", db_root_stage);
+		return -EINVAL;
+	}
+	filp_close(fp, 0);
+
+	strncpy(db_root, db_root_stage, read_bytes);
+
+	mutex_unlock(&g_tf_lock);
+
+	return read_bytes;
+}
+
+CONFIGFS_ATTR(target_core_item_, dbroot);
+
 static struct target_fabric_configfs *target_core_get_fabric(
 	const char *name)
 {
···
  */
 static struct configfs_attribute *target_core_fabric_item_attrs[] = {
 	&target_core_item_attr_version,
+	&target_core_item_attr_dbroot,
 	NULL,
 };
 

drivers/target/target_core_internal.h

···
 /* target_core_xcopy.c */
 extern struct se_portal_group xcopy_pt_tpg;
 
+/* target_core_configfs.c */
+#define DB_ROOT_LEN		4096
+#define	DB_ROOT_DEFAULT		"/var/target"
+
+extern char db_root[];
+
 #endif /* TARGET_CORE_INTERNAL_H */