From a3d1e7eb5abe3aa1095bc75d1a6760d3809bd672 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Mon, 18 Nov 2019 09:43:10 -0500
Subject: simple_recursive_removal(): kernel-side rm -rf for ramfs-style
 filesystems

two requirements: no file creations in IS_DEADDIR and no cross-directory
renames whatsoever.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/libfs.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

(limited to 'fs/libfs.c')

diff --git a/fs/libfs.c b/fs/libfs.c
index 1463b038ffc4..c686bd9caac6 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -19,6 +19,7 @@
 #include <linux/buffer_head.h> /* sync_mapping_buffers */
 #include <linux/fs_context.h>
 #include <linux/pseudo_fs.h>
+#include <linux/fsnotify.h>
 
 #include <linux/uaccess.h>
 
@@ -239,6 +240,75 @@ const struct inode_operations simple_dir_inode_operations = {
 };
 EXPORT_SYMBOL(simple_dir_inode_operations);
 
+static struct dentry *find_next_child(struct dentry *parent, struct dentry *prev)
+{
+	struct dentry *child = NULL;
+	struct list_head *p = prev ? &prev->d_child : &parent->d_subdirs;
+
+	spin_lock(&parent->d_lock);
+	while ((p = p->next) != &parent->d_subdirs) {
+		struct dentry *d = container_of(p, struct dentry, d_child);
+		if (simple_positive(d)) {
+			spin_lock_nested(&d->d_lock, DENTRY_D_LOCK_NESTED);
+			if (simple_positive(d))
+				child = dget_dlock(d);
+			spin_unlock(&d->d_lock);
+			if (likely(child))
+				break;
+		}
+	}
+	spin_unlock(&parent->d_lock);
+	dput(prev);
+	return child;
+}
+
+void simple_recursive_removal(struct dentry *dentry,
+                              void (*callback)(struct dentry *))
+{
+	struct dentry *this = dget(dentry);
+	while (true) {
+		struct dentry *victim = NULL, *child;
+		struct inode *inode = this->d_inode;
+
+		inode_lock(inode);
+		if (d_is_dir(this))
+			inode->i_flags |= S_DEAD;
+		while ((child = find_next_child(this, victim)) == NULL) {
+			// kill and ascend
+			// update metadata while it's still locked
+			inode->i_ctime = current_time(inode);
+			clear_nlink(inode);
+			inode_unlock(inode);
+			victim = this;
+			this = this->d_parent;
+			inode = this->d_inode;
+			inode_lock(inode);
+			if (simple_positive(victim)) {
+				d_invalidate(victim);	// avoid lost mounts
+				if (d_is_dir(victim))
+					fsnotify_rmdir(inode, victim);
+				else
+					fsnotify_unlink(inode, victim);
+				if (callback)
+					callback(victim);
+				dput(victim);		// unpin it
+			}
+			if (victim == dentry) {
+				inode->i_ctime = inode->i_mtime =
+					current_time(inode);
+				if (d_is_dir(dentry))
+					drop_nlink(inode);
+				inode_unlock(inode);
+				dput(dentry);
+				return;
+			}
+		}
+		inode_unlock(inode);
+		this = child;
+	}
+}
+EXPORT_SYMBOL(simple_recursive_removal);
+
 static const struct super_operations simple_super_operations = {
 	.statfs		= simple_statfs,
 };
-- 
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