[PATCH v2 0/4] configfs: implement committable items and add sample code

[PATCH v2 0/4] configfs: implement committable items and add sample code

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Committable items in configfs are well defined and documented but unfortunately
so far never implemented.

The use-case we have over at the GPIO subsystem is using configfs in
conjunction with sysfs to replace our current gpio-mockup testing module
with one that will be much more flexible and will allow complete coverage
of the GPIO uAPI.

The current gpio-mockup module is controlled using module parameters which
forces the user to reload it everytime they need to change the chip
configuration or layout and makes it difficult to extend its functionality.

Testing module based on configfs would allow fine-grained control over dummy
GPIO chips but since GPIO devices must be configured before they are
instantiated, we need committable items.

This implements them and adds code examples to configfs_sample module. The
first two patches are just cosmetic.

v1 -> v2:
- fix a 'set but not used' build warning reported by kernel test robot

Bartosz Golaszewski (4):
  configfs: increase the item name length
  configfs: use BIT() for internal flags
  configfs: implement committable items
  samples: configfs: add a committable group

 Documentation/filesystems/configfs.rst |   6 +-
 fs/configfs/configfs_internal.h        |  22 +--
 fs/configfs/dir.c                      | 237 ++++++++++++++++++++++++-
 fs/configfs/file.c                     |   8 +
 include/linux/configfs.h               |   3 +-
 samples/configfs/configfs_sample.c     | 150 ++++++++++++++++
 6 files changed, 406 insertions(+), 20 deletions(-)

-- 
2.29.1

[PATCH v2 1/4] configfs: increase the item name length

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

20 characters limit for item name is relatively small. Let's increase it
to 32 to fit '04-committable-children' - a name we'll use in the sample
code for committable items.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
---
 include/linux/configfs.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 2e8c69b43c64..4f76dcc08134 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -27,7 +27,7 @@
 #include <linux/kref.h>   /* struct kref */
 #include <linux/mutex.h>  /* struct mutex */
 
-#define CONFIGFS_ITEM_NAME_LEN	20
+#define CONFIGFS_ITEM_NAME_LEN	32
 
 struct module;
 
-- 
2.29.1

[PATCH v2 2/4] configfs: use BIT() for internal flags

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

For better readability and maintenance: use the BIT() macro for flag
definitions.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
---
 fs/configfs/configfs_internal.h | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index 22dce2d35a4b..855f00868654 100644
--- a/fs/configfs/configfs_internal.h
+++ b/fs/configfs/configfs_internal.h
@@ -46,16 +46,16 @@ struct configfs_dirent {
 	struct configfs_fragment *s_frag;
 };
 
-#define CONFIGFS_ROOT		0x0001
-#define CONFIGFS_DIR		0x0002
-#define CONFIGFS_ITEM_ATTR	0x0004
-#define CONFIGFS_ITEM_BIN_ATTR	0x0008
-#define CONFIGFS_ITEM_LINK	0x0020
-#define CONFIGFS_USET_DIR	0x0040
-#define CONFIGFS_USET_DEFAULT	0x0080
-#define CONFIGFS_USET_DROPPING	0x0100
-#define CONFIGFS_USET_IN_MKDIR	0x0200
-#define CONFIGFS_USET_CREATING	0x0400
+#define CONFIGFS_ROOT			BIT(0)
+#define CONFIGFS_DIR			BIT(1)
+#define CONFIGFS_ITEM_ATTR		BIT(2)
+#define CONFIGFS_ITEM_BIN_ATTR		BIT(3)
+#define CONFIGFS_ITEM_LINK		BIT(5)
+#define CONFIGFS_USET_DIR		BIT(6)
+#define CONFIGFS_USET_DEFAULT		BIT(7)
+#define CONFIGFS_USET_DROPPING		BIT(8)
+#define CONFIGFS_USET_IN_MKDIR		BIT(9)
+#define CONFIGFS_USET_CREATING		BIT(10)
 #define CONFIGFS_NOT_PINNED	(CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)
 
 extern struct mutex configfs_symlink_mutex;
-- 
2.29.1

[PATCH v2 3/4] configfs: implement committable items

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

This implements configfs committable items. We mostly follow the
documentation except that we extend config_group_ops with uncommit_item()
callback for reverting the changes made by commit_item().

Each committable group has two sub-directories: pending and live. New
items can only be created in pending/. Attributes can only be modified
while the item is in pending/. Once it's ready to be committed, it must
be moved over to live/ using the rename() system call. This is when the
commit_item() function will be called.

Implementation-wise: we reuse the default group mechanism to elegantly
plug the new pseude-groups into configfs. The pending group inherits the
parent group's operations so that config_items can be seamlesly created
in it using the callbacks supplied by the user as part of the committable
group itself.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
---
 Documentation/filesystems/configfs.rst |   6 +-
 fs/configfs/configfs_internal.h        |   2 +
 fs/configfs/dir.c                      | 237 ++++++++++++++++++++++++-
 fs/configfs/file.c                     |   8 +
 include/linux/configfs.h               |   1 +
 5 files changed, 245 insertions(+), 9 deletions(-)

diff --git a/Documentation/filesystems/configfs.rst b/Documentation/filesystems/configfs.rst
index 1d3d6f4a82a9..7e0e7c356450 100644
--- a/Documentation/filesystems/configfs.rst
+++ b/Documentation/filesystems/configfs.rst
@@ -290,6 +290,7 @@ config_item_type::
 		struct config_group *(*make_group)(struct config_group *group,
 						   const char *name);
 		int (*commit_item)(struct config_item *item);
+		int (*uncommit_item)(struct config_item *item);
 		void (*disconnect_notify)(struct config_group *group,
 					  struct config_item *item);
 		void (*drop_item)(struct config_group *group,
@@ -490,9 +491,6 @@ pass up an error.
 Committable Items
 =================
 
-Note:
-     Committable items are currently unimplemented.
-
 Some config_items cannot have a valid initial state.  That is, no
 default values can be specified for the item's attributes such that the
 item can do its work.  Userspace must configure one or more attributes,
@@ -532,4 +530,4 @@ method returns zero and the item is moved to the "live" directory.
 As rmdir(2) does not work in the "live" directory, an item must be
 shutdown, or "uncommitted".  Again, this is done via rename(2), this
 time from the "live" directory back to the "pending" one.  The subsystem
-is notified by the ct_group_ops->uncommit_object() method.
+is notified by the ct_group_ops->uncommit_item() method.
diff --git a/fs/configfs/configfs_internal.h b/fs/configfs/configfs_internal.h
index 855f00868654..22b649567b13 100644
--- a/fs/configfs/configfs_internal.h
+++ b/fs/configfs/configfs_internal.h
@@ -56,6 +56,8 @@ struct configfs_dirent {
 #define CONFIGFS_USET_DROPPING		BIT(8)
 #define CONFIGFS_USET_IN_MKDIR		BIT(9)
 #define CONFIGFS_USET_CREATING		BIT(10)
+#define CONFIGFS_GROUP_PENDING		BIT(11)
+#define CONFIGFS_GROUP_LIVE		BIT(12)
 #define CONFIGFS_NOT_PINNED	(CONFIGFS_ITEM_ATTR | CONFIGFS_ITEM_BIN_ATTR)
 
 extern struct mutex configfs_symlink_mutex;
diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c
index b0983e2a4e2c..cbd298681221 100644
--- a/fs/configfs/dir.c
+++ b/fs/configfs/dir.c
@@ -655,6 +655,13 @@ static void detach_groups(struct config_group *group)
 
 		inode_unlock(d_inode(child));
 
+		/*
+		 * Free memory allocated for the pending and live directories
+		 * of committable groups.
+		 */
+		if (sd->s_type & (CONFIGFS_GROUP_PENDING | CONFIGFS_GROUP_LIVE))
+			kfree(sd->s_element);
+
 		d_delete(child);
 		dput(child);
 	}
@@ -859,6 +866,133 @@ static void configfs_detach_item(struct config_item *item)
 	configfs_remove_dir(item);
 }
 
+static bool is_committable_group(struct config_item *item)
+{
+	const struct config_item_type *type = item->ci_type;
+
+	if (type && type->ct_group_ops &&
+	    type->ct_group_ops->commit_item &&
+	    type->ct_group_ops->uncommit_item)
+		return true;
+
+	return false;
+}
+
+struct pending_group_data {
+	struct config_group group;
+	struct config_item_type type;
+	struct configfs_group_operations group_ops;
+};
+
+struct live_group_data {
+	struct config_group group;
+	struct config_item_type type;
+};
+
+static int create_pending_group(struct config_item *parent_item,
+				struct configfs_fragment *frag)
+{
+	const struct config_item_type *parent_type = parent_item->ci_type;
+	struct pending_group_data *pending;
+	struct configfs_dirent *sd;
+	int ret;
+
+	pending = kzalloc(sizeof(*pending), GFP_KERNEL);
+	if (!pending)
+		return -ENOMEM;
+
+	/*
+	 * Let's inherit the group_ops from the parent except for item
+	 * committing and uncommitting.
+	 */
+	memcpy(&pending->group_ops, parent_type->ct_group_ops,
+	       sizeof(struct configfs_group_operations));
+	pending->type.ct_group_ops = &pending->group_ops;
+	pending->type.ct_group_ops->commit_item = NULL;
+	pending->type.ct_group_ops->uncommit_item = NULL;
+
+	/* Let's directly reuse item_ops. */
+	pending->type.ct_item_ops = parent_type->ct_item_ops;
+	pending->type.ct_owner = parent_type->ct_owner;
+
+	config_group_init_type_name(&pending->group, "pending", &pending->type);
+
+	ret = create_default_group(to_config_group(parent_item),
+				   &pending->group, frag);
+	if (ret) {
+		kfree(pending);
+		return ret;
+	}
+
+	link_group(to_config_group(parent_item), &pending->group);
+
+	sd = pending->group.cg_item.ci_dentry->d_fsdata;
+	/* Allow creating config_items in 'pending' group. */
+	sd->s_type |= (CONFIGFS_GROUP_PENDING | CONFIGFS_USET_DIR);
+
+	return 0;
+}
+
+static int create_live_group(struct config_item *parent_item,
+			     struct configfs_fragment *frag)
+{
+	struct live_group_data *live;
+	struct configfs_dirent *sd;
+	int ret;
+
+	live = kzalloc(sizeof(*live), GFP_KERNEL);
+	if (!live)
+		return -ENOMEM;
+
+	live->type.ct_owner = parent_item->ci_type->ct_owner;
+
+	config_group_init_type_name(&live->group, "live", &live->type);
+
+	ret = create_default_group(to_config_group(parent_item),
+				   &live->group, frag);
+	if (ret) {
+		kfree(live);
+		return ret;
+	}
+
+	link_group(to_config_group(parent_item), &live->group);
+
+	sd = live->group.cg_item.ci_dentry->d_fsdata;
+	sd->s_type |= CONFIGFS_GROUP_LIVE;
+
+	return 0;
+}
+
+static int create_committable_groups(struct config_item *parent_item,
+				     struct configfs_fragment *frag)
+{
+	struct configfs_dirent *sd;
+	int ret;
+
+	ret = create_pending_group(parent_item, frag);
+	if (ret)
+		return ret;
+
+	ret = create_live_group(parent_item, frag);
+	if (ret) {
+		detach_groups(to_config_group(parent_item));
+		return ret;
+	}
+
+	/* Disallow creating items directly in the committable group. */
+	sd = parent_item->ci_dentry->d_fsdata;
+	sd->s_type &= ~CONFIGFS_USET_DIR;
+
+	return 0;
+}
+
+static void dentry_mark_dead(struct config_item *item, struct dentry *dentry)
+{
+	configfs_detach_item(item);
+	d_inode(dentry)->i_flags |= S_DEAD;
+	dont_mount(dentry);
+}
+
 static int configfs_attach_group(struct config_item *parent_item,
 				 struct config_item *item,
 				 struct dentry *dentry,
@@ -884,11 +1018,15 @@ static int configfs_attach_group(struct config_item *parent_item,
 		inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
 		configfs_adjust_dir_dirent_depth_before_populate(sd);
 		ret = populate_groups(to_config_group(item), frag);
-		if (ret) {
-			configfs_detach_item(item);
-			d_inode(dentry)->i_flags |= S_DEAD;
-			dont_mount(dentry);
+		if (ret)
+			dentry_mark_dead(item, dentry);
+
+		if (is_committable_group(item)) {
+			ret = create_committable_groups(item, frag);
+			if (ret)
+				dentry_mark_dead(item, dentry);
 		}
+
 		configfs_adjust_dir_dirent_depth_after_populate(sd);
 		inode_unlock(d_inode(dentry));
 		if (ret)
@@ -1455,7 +1593,7 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 	struct config_item *parent_item;
 	struct config_item *item;
 	struct configfs_subsystem *subsys;
-	struct configfs_dirent *sd;
+	struct configfs_dirent *sd, *parent_sd;
 	struct configfs_fragment *frag;
 	struct module *subsys_owner = NULL, *dead_item_owner = NULL;
 	int ret;
@@ -1474,6 +1612,12 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 		return -EINVAL;
 	}
 
+	parent_sd = dentry->d_parent->d_fsdata;
+	if (parent_sd->s_type & CONFIGFS_GROUP_LIVE) {
+		config_item_put(parent_item);
+		return -EPERM;
+	}
+
 	/* configfs_mkdir() shouldn't have allowed this */
 	BUG_ON(!subsys->su_group.cg_item.ci_type);
 	subsys_owner = subsys->su_group.cg_item.ci_type->ct_owner;
@@ -1560,9 +1704,92 @@ static int configfs_rmdir(struct inode *dir, struct dentry *dentry)
 	return 0;
 }
 
+static int configfs_rename(struct inode *old_dir, struct dentry *old_dentry,
+			   struct inode *new_dir, struct dentry *new_dentry,
+			   unsigned int flags)
+{
+	struct configfs_dirent *sd, *old_parent_sd, *new_parent_sd;
+	struct dentry *old_parent_dentry, *new_parent_dentry;
+	struct dentry *committable_group_dentry;
+	struct config_item *committable_group_item, *item, *new_parent_item;
+	struct configfs_subsystem *committable_group_subsys;
+	struct configfs_group_operations *committable_group_ops;
+	int ret = 0;
+
+	if (flags)
+		return -EINVAL;
+
+	old_parent_dentry = old_dentry->d_parent;
+	new_parent_dentry = new_dentry->d_parent;
+
+	sd = old_dentry->d_fsdata;
+	old_parent_sd = old_dentry->d_parent->d_fsdata;
+	new_parent_sd = new_dentry->d_parent->d_fsdata;
+
+	if (!old_parent_sd || !new_parent_sd)
+		return -EPERM;
+
+	/*
+	 * Renaming must always be between a 'pending' and a 'live' group and
+	 * both need to have the same parent.
+	 */
+	if (!((old_parent_sd->s_type & CONFIGFS_GROUP_PENDING) &&
+	      (new_parent_sd->s_type & CONFIGFS_GROUP_LIVE)) &&
+	    !((old_parent_sd->s_type & CONFIGFS_GROUP_LIVE) &&
+	      (new_parent_sd->s_type & CONFIGFS_GROUP_PENDING)))
+		return -EPERM;
+
+	if (old_parent_dentry->d_parent != new_parent_dentry->d_parent)
+		return -EPERM;
+
+	committable_group_dentry = old_parent_dentry->d_parent;
+	/*
+	 * Grab a reference to the committable group for the duration of
+	 * this function.
+	 */
+	committable_group_item =
+		configfs_get_config_item(committable_group_dentry);
+	committable_group_subsys =
+		to_config_group(committable_group_item)->cg_subsys;
+	committable_group_ops = committable_group_item->ci_type->ct_group_ops;
+
+	item = sd->s_element;
+	new_parent_item = new_parent_sd->s_element;
+
+	if (WARN_ON(!is_committable_group(committable_group_item))) {
+		/* This would be a result of a programming error in configfs. */
+		config_item_put(committable_group_item);
+		return -EPERM;
+	}
+
+	mutex_lock(&committable_group_subsys->su_mutex);
+	spin_lock(&configfs_dirent_lock);
+
+	if ((old_parent_sd->s_type & CONFIGFS_GROUP_PENDING) &&
+	    (new_parent_sd->s_type & CONFIGFS_GROUP_LIVE))
+		ret = committable_group_ops->commit_item(item);
+	else
+		ret = committable_group_ops->uncommit_item(item);
+	if (ret)
+		goto out;
+
+	new_dentry->d_fsdata = sd;
+	list_move(&sd->s_sibling, &new_parent_sd->s_children);
+	item->ci_parent = new_parent_item;
+	d_move(old_dentry, new_dentry);
+
+out:
+	spin_unlock(&configfs_dirent_lock);
+	mutex_unlock(&committable_group_subsys->su_mutex);
+	config_item_put(committable_group_item);
+
+	return ret;
+}
+
 const struct inode_operations configfs_dir_inode_operations = {
 	.mkdir		= configfs_mkdir,
 	.rmdir		= configfs_rmdir,
+	.rename		= configfs_rename,
 	.symlink	= configfs_symlink,
 	.unlink		= configfs_unlink,
 	.lookup		= configfs_lookup,
diff --git a/fs/configfs/file.c b/fs/configfs/file.c
index 1f0270229d7b..a20e55fd05e8 100644
--- a/fs/configfs/file.c
+++ b/fs/configfs/file.c
@@ -243,9 +243,17 @@ fill_write_buffer(struct configfs_buffer * buffer, const char __user * buf, size
 static int
 flush_write_buffer(struct file *file, struct configfs_buffer *buffer, size_t count)
 {
+	struct config_item *parent_item = buffer->item->ci_parent;
 	struct configfs_fragment *frag = to_frag(file);
+	struct configfs_dirent *sd;
 	int res = -ENOENT;
 
+	if (parent_item && parent_item->ci_dentry) {
+		sd = parent_item->ci_dentry->d_fsdata;
+		if (sd->s_type & CONFIGFS_GROUP_LIVE)
+			return -EPERM;
+	}
+
 	down_read(&frag->frag_sem);
 	if (!frag->frag_dead)
 		res = buffer->attr->store(buffer->item, buffer->page, count);
diff --git a/include/linux/configfs.h b/include/linux/configfs.h
index 4f76dcc08134..ff6b0e408136 100644
--- a/include/linux/configfs.h
+++ b/include/linux/configfs.h
@@ -219,6 +219,7 @@ struct configfs_group_operations {
 	struct config_item *(*make_item)(struct config_group *group, const char *name);
 	struct config_group *(*make_group)(struct config_group *group, const char *name);
 	int (*commit_item)(struct config_item *item);
+	int (*uncommit_item)(struct config_item *item);
 	void (*disconnect_notify)(struct config_group *group, struct config_item *item);
 	void (*drop_item)(struct config_group *group, struct config_item *item);
 };
-- 
2.29.1

[PATCH v2 4/4] samples: configfs: add a committable group

[Bartosz Golaszewski]

From: Bartosz Golaszewski <bgolaszewski@baylibre.com>

Add an example of using committable items to configfs samples. Each
config item has two attributes: read-write 'storeme' which works
similarly to other examples in this file and a read-only 'committed'
attribute which changes its value between false and true depending on
whether it's committed or not at the moment.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
---
 samples/configfs/configfs_sample.c | 150 +++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)

diff --git a/samples/configfs/configfs_sample.c b/samples/configfs/configfs_sample.c
index f9008be7a8a1..08fc22c7aa55 100644
--- a/samples/configfs/configfs_sample.c
+++ b/samples/configfs/configfs_sample.c
@@ -315,6 +315,155 @@ static struct configfs_subsystem group_children_subsys = {
 
 /* ----------------------------------------------------------------- */
 
+/*
+ * 04-committable-children
+ *
+ * This is an example of a committable group.  It's similar to the simple
+ * children example but each config_item has an additional 'committed'
+ * attribute which is read-only and is only modified when the config_item
+ * is moved from the 'pending' to the 'live' directory.
+ */
+
+struct committable_child {
+	struct config_item item;
+	int storeme;
+	bool committed;
+};
+
+static inline struct committable_child *
+to_committable_child(struct config_item *item)
+{
+	return container_of(item, struct committable_child, item);
+}
+
+static ssize_t
+committable_child_storeme_show(struct config_item *item, char *page)
+{
+	return sprintf(page, "%d\n", to_committable_child(item)->storeme);
+}
+
+static ssize_t committable_child_storeme_store(struct config_item *item,
+					       const char *page, size_t count)
+{
+	struct committable_child *child = to_committable_child(item);
+	int ret;
+
+	ret = kstrtoint(page, 10, &child->storeme);
+	if (ret)
+		return ret;
+
+	return count;
+}
+
+CONFIGFS_ATTR(committable_child_, storeme);
+
+static ssize_t
+committable_child_committed_show(struct config_item *item, char *page)
+{
+	return sprintf(page, "%s\n",
+		to_committable_child(item)->committed ? "true" : "false");
+}
+
+CONFIGFS_ATTR_RO(committable_child_, committed);
+
+static struct configfs_attribute *committable_child_attrs[] = {
+	&committable_child_attr_storeme,
+	&committable_child_attr_committed,
+	NULL,
+};
+
+static void committable_child_release(struct config_item *item)
+{
+	kfree(to_committable_child(item));
+}
+
+static struct configfs_item_operations committable_child_item_ops = {
+	.release	= committable_child_release,
+};
+
+static const struct config_item_type committable_child_type = {
+	.ct_item_ops	= &committable_child_item_ops,
+	.ct_attrs	= committable_child_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+struct committable_children {
+	struct config_group group;
+};
+
+static struct config_item *
+committable_children_make_item(struct config_group *group, const char *name)
+{
+	struct committable_child *child;
+
+	child = kzalloc(sizeof(*child), GFP_KERNEL);
+	if (!child)
+		return ERR_PTR(-ENOMEM);
+
+	config_item_init_type_name(&child->item, name, &committable_child_type);
+
+	return &child->item;
+}
+
+static ssize_t
+committable_children_description_show(struct config_item *item, char *page)
+{
+	return sprintf(page,
+"[04-committable-children]\n"
+"\n"
+"This subsystem allows creation of committable config_items.  The subsystem\n"
+"has two subdirectories: pending and live.  New config_items can only be\n"
+"created in pending/ and they have one writable and readable attribute as\n"
+"well as a single read-only attribute.  The latter is only changed once the\n"
+"item is 'committed'.  This is done by moving the config_item (using\n"
+"rename()) to the live/ directory.  At that point even the read-write\n"
+"attributes can no longer be written to.\n");
+}
+
+CONFIGFS_ATTR_RO(committable_children_, description);
+
+static struct configfs_attribute *committable_children_attrs[] = {
+	&committable_children_attr_description,
+	NULL,
+};
+
+static int committable_children_commit_item(struct config_item *item)
+{
+	to_committable_child(item)->committed = true;
+
+	return 0;
+}
+
+static int committable_children_uncommit_item(struct config_item *item)
+{
+	to_committable_child(item)->committed = false;
+
+	return 0;
+}
+
+static struct configfs_group_operations committable_children_group_ops = {
+	.make_item	= committable_children_make_item,
+	.commit_item	= committable_children_commit_item,
+	.uncommit_item	= committable_children_uncommit_item,
+};
+
+static const struct config_item_type committable_children_type = {
+	.ct_group_ops	= &committable_children_group_ops,
+	.ct_attrs	= committable_children_attrs,
+	.ct_owner	= THIS_MODULE,
+};
+
+static struct configfs_subsystem committable_children_subsys = {
+	.su_group = {
+		.cg_item = {
+			.ci_namebuf = "04-committable-children",
+			.ci_type = &committable_children_type,
+		},
+	},
+};
+
+/* ----------------------------------------------------------------- */
+
 /*
  * We're now done with our subsystem definitions.
  * For convenience in this module, here's a list of them all.  It
@@ -326,6 +475,7 @@ static struct configfs_subsystem *example_subsys[] = {
 	&childless_subsys.subsys,
 	&simple_children_subsys,
 	&group_children_subsys,
+	&committable_children_subsys,
 	NULL,
 };
 
-- 
2.29.1

Re: [PATCH v2 2/4] configfs: use BIT() for internal flags

[Christoph Hellwig]

On Mon, Nov 30, 2020 at 05:47:02PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> 
> For better readability and maintenance: use the BIT() macro for flag
> definitions.

This does not improve readability, as I now need to look up a macro,
one that doesn't make any sense at all.  If you really prefer bit based
numbering just use the totally obvious (1 << bit) syntax.

Re: [PATCH v2 3/4] configfs: implement committable items

[Christoph Hellwig]

On Mon, Nov 30, 2020 at 05:47:03PM +0100, Bartosz Golaszewski wrote:
> From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> 
> This implements configfs committable items. We mostly follow the
> documentation except that we extend config_group_ops with uncommit_item()
> callback for reverting the changes made by commit_item().
> 
> Each committable group has two sub-directories: pending and live. New
> items can only be created in pending/. Attributes can only be modified
> while the item is in pending/. Once it's ready to be committed, it must
> be moved over to live/ using the rename() system call. This is when the
> commit_item() function will be called.
> 
> Implementation-wise: we reuse the default group mechanism to elegantly
> plug the new pseude-groups into configfs. The pending group inherits the
> parent group's operations so that config_items can be seamlesly created
> in it using the callbacks supplied by the user as part of the committable
> group itself.

This looks pretty awkward in the hierachy, but I can't really think
of anything else.  One idea would be to require fsync to stage updates,
but that isn't really very well discoverable.

Re: [PATCH v2 3/4] configfs: implement committable items

[Bartosz Golaszewski]

On Tue, Dec 1, 2020 at 12:26 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Mon, Nov 30, 2020 at 05:47:03PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > This implements configfs committable items. We mostly follow the
> > documentation except that we extend config_group_ops with uncommit_item()
> > callback for reverting the changes made by commit_item().
> >
> > Each committable group has two sub-directories: pending and live. New
> > items can only be created in pending/. Attributes can only be modified
> > while the item is in pending/. Once it's ready to be committed, it must
> > be moved over to live/ using the rename() system call. This is when the
> > commit_item() function will be called.
> >
> > Implementation-wise: we reuse the default group mechanism to elegantly
> > plug the new pseude-groups into configfs. The pending group inherits the
> > parent group's operations so that config_items can be seamlesly created
> > in it using the callbacks supplied by the user as part of the committable
> > group itself.
>
> This looks pretty awkward in the hierachy, but I can't really think
> of anything else.  One idea would be to require fsync to stage updates,
> but that isn't really very well discoverable.

I'm not sure how that would work. fsync() a directory once the item is
configured to instantiate it?

I was thinking about different solutions other than the one already
defined but it always requires at least some kind of an additional
attribute (not defined by the user) to "commit" an item and in the end
rename() looks like a good candidate to me. We could possibly drop the
pending and live groups and simple use a magic suffix for committed
items e.g.: `mv myitem myitem_committed` but this would be even less
intuitive.

If this patch is extended with:

@@ -1103,6 +1103,8 @@ static void configfs_dump_one(struct
configfs_dirent *sd, int level)
  type_print(CONFIGFS_USET_DIR);
  type_print(CONFIGFS_USET_DEFAULT);
  type_print(CONFIGFS_USET_DROPPING);
+ type_print(CONFIGFS_GROUP_PENDING);
+ type_print(CONFIGFS_GROUP_LIVE);
 #undef type_print
 }

Then dumping the committable subsystem shows:

[  133.603035] configfs:    "04-committable-children":
[  133.603045] configfs:     CONFIGFS_DIR
[  133.603050] configfs:      "live":
[  133.603054] configfs:       CONFIGFS_DIR
[  133.603058] configfs:       CONFIGFS_USET_DIR
[  133.603062] configfs:       CONFIGFS_USET_DEFAULT
[  133.603066] configfs:       CONFIGFS_GROUP_LIVE
[  133.603070] configfs:        "dupa":
[  133.603074] configfs:         CONFIGFS_DIR
[  133.603078] configfs:          "committed":
[  133.603082] configfs:           CONFIGFS_ITEM_ATTR
[  133.603086] configfs:          "storeme":
[  133.603090] configfs:           CONFIGFS_ITEM_ATTR
[  133.603094] configfs:      "pending":
[  133.603160] configfs:       CONFIGFS_DIR
[  133.603167] configfs:       CONFIGFS_USET_DIR
[  133.603175] configfs:       CONFIGFS_USET_DEFAULT
[  133.603183] configfs:       CONFIGFS_GROUP_PENDING
[  133.603191] configfs:      "description":
[  133.603198] configfs:       CONFIGFS_ITEM_ATTR

Which doesn't look that bad IMO.

Bartosz

Re: [PATCH v2 2/4] configfs: use BIT() for internal flags

[Bartosz Golaszewski]

On Tue, Dec 1, 2020 at 12:22 PM Christoph Hellwig <hch@lst.de> wrote:
>
> On Mon, Nov 30, 2020 at 05:47:02PM +0100, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bgolaszewski@baylibre.com>
> >
> > For better readability and maintenance: use the BIT() macro for flag
> > definitions.
>
> This does not improve readability, as I now need to look up a macro,
> one that doesn't make any sense at all.  If you really prefer bit based
> numbering just use the totally obvious (1 << bit) syntax.

(1 << bit) is better than a number in hex but BIT() has been in the
kernel for so long that I doubt anyone needs to look it up.

Anyway, it's your call, it'll be (1 << bit) in v3.

Bartosz