kernfs: add kernfs_ops->open/release() callbacks

Add ->open/release() methods to kernfs_ops.  ->open() is called when
the file is opened and ->release() when the file is either released or
severed.  These callbacks can be used, for example, to manage
persistent caching objects over multiple seq_file iterations.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Acked-by: Zefan Li <lizefan@huawei.com>

1 files changed, 45 insertions, 6 deletions

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index d0b6fb13ead0..20c396291ac1 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -708,7 +708,8 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
 	if (error)
 		goto err_free;
 
-	((struct seq_file *)file->private_data)->private = of;
+	of->seq_file = file->private_data;
+	of->seq_file->private = of;
 
 	/* seq_file clears PWRITE unconditionally, restore it if WRITE */
 	if (file->f_mode & FMODE_WRITE)
@@ -717,13 +718,22 @@ static int kernfs_fop_open(struct inode *inode, struct file *file)
 	/* make sure we have open node struct */
 	error = kernfs_get_open_node(kn, of);
 	if (error)
-		goto err_close;
+		goto err_seq_release;
+
+	if (ops->open) {
+		/* nobody has access to @of yet, skip @of->mutex */
+		error = ops->open(of);
+		if (error)
+			goto err_put_node;
+	}
 
 	/* open succeeded, put active references */
 	kernfs_put_active(kn);
 	return 0;
 
-err_close:
+err_put_node:
+	kernfs_put_open_node(kn, of);
+err_seq_release:
 	seq_release(inode, file);
 err_free:
 	kfree(of->prealloc_buf);
@@ -733,11 +743,32 @@ err_out:
 	return error;
 }
 
+/* used from release/drain to ensure that ->release() is called exactly once */
+static void kernfs_release_file(struct kernfs_node *kn,
+				struct kernfs_open_file *of)
+{
+	if (!(kn->flags & KERNFS_HAS_RELEASE))
+		return;
+
+	mutex_lock(&of->mutex);
+	if (!of->released) {
+		/*
+		 * A file is never detached without being released and we
+		 * need to be able to release files which are deactivated
+		 * and being drained.  Don't use kernfs_ops().
+		 */
+		kn->attr.ops->release(of);
+		of->released = true;
+	}
+	mutex_unlock(&of->mutex);
+}
+
 static int kernfs_fop_release(struct inode *inode, struct file *filp)
 {
 	struct kernfs_node *kn = filp->f_path.dentry->d_fsdata;
 	struct kernfs_open_file *of = kernfs_of(filp);
 
+	kernfs_release_file(kn, of);
 	kernfs_put_open_node(kn, of);
 	seq_release(inode, filp);
 	kfree(of->prealloc_buf);
@@ -746,12 +777,12 @@ static int kernfs_fop_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
-void kernfs_unmap_bin_file(struct kernfs_node *kn)
+void kernfs_drain_open_files(struct kernfs_node *kn)
 {
 	struct kernfs_open_node *on;
 	struct kernfs_open_file *of;
 
-	if (!(kn->flags & KERNFS_HAS_MMAP))
+	if (!(kn->flags & (KERNFS_HAS_MMAP | KERNFS_HAS_RELEASE)))
 		return;
 
 	spin_lock_irq(&kernfs_open_node_lock);
@@ -763,10 +794,16 @@ void kernfs_unmap_bin_file(struct kernfs_node *kn)
 		return;
 
 	mutex_lock(&kernfs_open_file_mutex);
+
 	list_for_each_entry(of, &on->files, list) {
 		struct inode *inode = file_inode(of->file);
-		unmap_mapping_range(inode->i_mapping, 0, 0, 1);
+
+		if (kn->flags & KERNFS_HAS_MMAP)
+			unmap_mapping_range(inode->i_mapping, 0, 0, 1);
+
+		kernfs_release_file(kn, of);
 	}
+
 	mutex_unlock(&kernfs_open_file_mutex);
 
 	kernfs_put_open_node(kn, NULL);
@@ -965,6 +1002,8 @@ struct kernfs_node *__kernfs_create_file(struct kernfs_node *parent,
 		kn->flags |= KERNFS_HAS_SEQ_SHOW;
 	if (ops->mmap)
 		kn->flags |= KERNFS_HAS_MMAP;
+	if (ops->release)
+		kn->flags |= KERNFS_HAS_RELEASE;
 
 	rc = kernfs_add_one(kn);
 	if (rc) {