/* Mark that we've taken i_mutex */
sd->s_type |= CONFIGFS_USET_DROPPING;
+ /*
+ * Yup, recursive. If there's a problem, blame
+ * deep nesting of default_groups
+ */
ret = configfs_detach_prep(sd->s_dentry);
if (!ret)
continue;
config_item_put(item);
}
+#ifdef DEBUG
+static void configfs_dump_one(struct configfs_dirent *sd, int level)
+{
+ printk(KERN_INFO "%*s\"%s\":\n", level, " ", configfs_get_name(sd));
+
+#define type_print(_type) if (sd->s_type & _type) printk(KERN_INFO "%*s %s\n", level, " ", #_type);
+ type_print(CONFIGFS_ROOT);
+ type_print(CONFIGFS_DIR);
+ type_print(CONFIGFS_ITEM_ATTR);
+ type_print(CONFIGFS_ITEM_LINK);
+ type_print(CONFIGFS_USET_DIR);
+ type_print(CONFIGFS_USET_DEFAULT);
+ type_print(CONFIGFS_USET_DROPPING);
+#undef type_print
+}
+
+static int configfs_dump(struct configfs_dirent *sd, int level)
+{
+ struct configfs_dirent *child_sd;
+ int ret = 0;
+
+ configfs_dump_one(sd, level);
+
+ if (!(sd->s_type & (CONFIGFS_DIR|CONFIGFS_ROOT)))
+ return 0;
+
+ list_for_each_entry(child_sd, &sd->s_children, s_sibling) {
+ ret = configfs_dump(child_sd, level + 2);
+ if (ret)
+ break;
+ }
+
+ return ret;
+}
+#endif
+
+
+/*
+ * configfs_depend_item() and configfs_undepend_item()
+ *
+ * WARNING: Do not call these from a configfs callback!
+ *
+ * This describes these functions and their helpers.
+ *
+ * Allow another kernel system to depend on a config_item. If this
+ * happens, the item cannot go away until the dependant can live without
+ * it. The idea is to give client modules as simple an interface as
+ * possible. When a system asks them to depend on an item, they just
+ * call configfs_depend_item(). If the item is live and the client
+ * driver is in good shape, we'll happily do the work for them.
+ *
+ * Why is the locking complex? Because configfs uses the VFS to handle
+ * all locking, but this function is called outside the normal
+ * VFS->configfs path. So it must take VFS locks to prevent the
+ * VFS->configfs stuff (configfs_mkdir(), configfs_rmdir(), etc). This is
+ * why you can't call these functions underneath configfs callbacks.
+ *
+ * Note, btw, that this can be called at *any* time, even when a configfs
+ * subsystem isn't registered, or when configfs is loading or unloading.
+ * Just like configfs_register_subsystem(). So we take the same
+ * precautions. We pin the filesystem. We lock each i_mutex _in_order_
+ * on our way down the tree. If we can find the target item in the
+ * configfs tree, it must be part of the subsystem tree as well, so we
+ * do not need the subsystem semaphore. Holding the i_mutex chain locks
+ * out mkdir() and rmdir(), who might be racing us.
+ */
+
+/*
+ * configfs_depend_prep()
+ *
+ * Only subdirectories count here. Files (CONFIGFS_NOT_PINNED) are
+ * attributes. This is similar but not the same to configfs_detach_prep().
+ * Note that configfs_detach_prep() expects the parent to be locked when it
+ * is called, but we lock the parent *inside* configfs_depend_prep(). We
+ * do that so we can unlock it if we find nothing.
+ *
+ * Here we do a depth-first search of the dentry hierarchy looking for
+ * our object. We take i_mutex on each step of the way down. IT IS
+ * ESSENTIAL THAT i_mutex LOCKING IS ORDERED. If we come back up a branch,
+ * we'll drop the i_mutex.
+ *
+ * If the target is not found, -ENOENT is bubbled up and we have released
+ * all locks. If the target was found, the locks will be cleared by
+ * configfs_depend_rollback().
+ *
+ * This adds a requirement that all config_items be unique!
+ *
+ * This is recursive because the locking traversal is tricky. There isn't
+ * much on the stack, though, so folks that need this function - be careful
+ * about your stack! Patches will be accepted to make it iterative.
+ */
+static int configfs_depend_prep(struct dentry *origin,
+ struct config_item *target)
+{
+ struct configfs_dirent *child_sd, *sd = origin->d_fsdata;
+ int ret = 0;
+
+ BUG_ON(!origin || !sd);
+
+ /* Lock this guy on the way down */
+ mutex_lock(&sd->s_dentry->d_inode->i_mutex);
+ if (sd->s_element == target) /* Boo-yah */
+ goto out;
+
+ list_for_each_entry(child_sd, &sd->s_children, s_sibling) {
+ if (child_sd->s_type & CONFIGFS_DIR) {
+ ret = configfs_depend_prep(child_sd->s_dentry,
+ target);
+ if (!ret)
+ goto out; /* Child path boo-yah */
+ }
+ }
+
+ /* We looped all our children and didn't find target */
+ mutex_unlock(&sd->s_dentry->d_inode->i_mutex);
+ ret = -ENOENT;
+
+out:
+ return ret;
+}
+
+/*
+ * This is ONLY called if configfs_depend_prep() did its job. So we can
+ * trust the entire path from item back up to origin.
+ *
+ * We walk backwards from item, unlocking each i_mutex. We finish by
+ * unlocking origin.
+ */
+static void configfs_depend_rollback(struct dentry *origin,
+ struct config_item *item)
+{
+ struct dentry *dentry = item->ci_dentry;
+
+ while (dentry != origin) {
+ mutex_unlock(&dentry->d_inode->i_mutex);
+ dentry = dentry->d_parent;
+ }
+
+ mutex_unlock(&origin->d_inode->i_mutex);
+}
+
+int configfs_depend_item(struct configfs_subsystem *subsys,
+ struct config_item *target)
+{
+ int ret;
+ struct configfs_dirent *p, *root_sd, *subsys_sd = NULL;
+ struct config_item *s_item = &subsys->su_group.cg_item;
+
+ /*
+ * Pin the configfs filesystem. This means we can safely access
+ * the root of the configfs filesystem.
+ */
+ ret = configfs_pin_fs();
+ if (ret)
+ return ret;
+
+ /*
+ * Next, lock the root directory. We're going to check that the
+ * subsystem is really registered, and so we need to lock out
+ * configfs_[un]register_subsystem().
+ */
+ mutex_lock(&configfs_sb->s_root->d_inode->i_mutex);
+
+ root_sd = configfs_sb->s_root->d_fsdata;
+
+ list_for_each_entry(p, &root_sd->s_children, s_sibling) {
+ if (p->s_type & CONFIGFS_DIR) {
+ if (p->s_element == s_item) {
+ subsys_sd = p;
+ break;
+ }
+ }
+ }
+
+ if (!subsys_sd) {
+ ret = -ENOENT;
+ goto out_unlock_fs;
+ }
+
+ /* Ok, now we can trust subsys/s_item */
+
+ /* Scan the tree, locking i_mutex recursively, return 0 if found */
+ ret = configfs_depend_prep(subsys_sd->s_dentry, target);
+ if (ret)
+ goto out_unlock_fs;
+
+ /* We hold all i_mutexes from the subsystem down to the target */
+ p = target->ci_dentry->d_fsdata;
+ p->s_dependent_count += 1;
+
+ configfs_depend_rollback(subsys_sd->s_dentry, target);
+
+out_unlock_fs:
+ mutex_unlock(&configfs_sb->s_root->d_inode->i_mutex);
+
+ /*
+ * If we succeeded, the fs is pinned via other methods. If not,
+ * we're done with it anyway. So release_fs() is always right.
+ */
+ configfs_release_fs();
+
+ return ret;
+}
+EXPORT_SYMBOL(configfs_depend_item);
+
+/*
+ * Release the dependent linkage. This is much simpler than
+ * configfs_depend_item() because we know that that the client driver is
+ * pinned, thus the subsystem is pinned, and therefore configfs is pinned.
+ */
+void configfs_undepend_item(struct configfs_subsystem *subsys,
+ struct config_item *target)
+{
+ struct configfs_dirent *sd;
+
+ /*
+ * Since we can trust everything is pinned, we just need i_mutex
+ * on the item.
+ */
+ mutex_lock(&target->ci_dentry->d_inode->i_mutex);
+
+ sd = target->ci_dentry->d_fsdata;
+ BUG_ON(sd->s_dependent_count < 1);
+
+ sd->s_dependent_count -= 1;
+
+ /*
+ * After this unlock, we cannot trust the item to stay alive!
+ * DO NOT REFERENCE item after this unlock.
+ */
+ mutex_unlock(&target->ci_dentry->d_inode->i_mutex);
+}
+EXPORT_SYMBOL(configfs_undepend_item);
static int configfs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
if (sd->s_type & CONFIGFS_USET_DEFAULT)
return -EPERM;
+ /*
+ * Here's where we check for dependents. We're protected by
+ * i_mutex.
+ */
+ if (sd->s_dependent_count)
+ return -EBUSY;
+
/* Get a working ref until we have the child */
parent_item = configfs_get_config_item(dentry->d_parent);
subsys = to_config_group(parent_item)->cg_subsys;
projects / linux-2.6 / commitdiff