[PATCH v2 02/14] fs: create simple_remove() helper

From: Amir Goldstein <amir73il@gmail.com>
To: Jan Kara <jack@suse.cz>
Cc: Matthew Bobrowski <mbobrowski@mbobrowski.org>,
	linux-fsdevel@vger.kernel.org
Subject: [PATCH v2 02/14] fs: create simple_remove() helper
Date: Thu, 16 May 2019 13:26:29 +0300	[thread overview]
Message-ID: <20190516102641.6574-3-amir73il@gmail.com> (raw)
In-Reply-To: <20190516102641.6574-1-amir73il@gmail.com>

There is a common pattern among pseudo filesystems for removing a dentry
from code paths that are NOT coming from vfs_{unlink,rmdir}, using a
combination of simple_{unlink,rmdir} and d_delete().

Create an helper to perform this common operation.  This helper is going
to be used as a place holder for the new fsnotify_{unlink,rmdir} hooks.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/libfs.c         | 27 +++++++++++++++++++++++++++
 include/linux/fs.h |  1 +
 2 files changed, 28 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index 4b59b1816efb..ca1132f1d5c6 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -353,6 +353,33 @@ int simple_rmdir(struct inode *dir, struct dentry *dentry)
 }
 EXPORT_SYMBOL(simple_rmdir);
 
+/*
+ * Unlike simple_unlink/rmdir, this helper is NOT called from vfs_unlink/rmdir.
+ * Caller must guaranty that d_parent and d_name are stable.
+ */
+int simple_remove(struct inode *dir, struct dentry *dentry)
+{
+	int ret;
+
+	/*
+	 * 'simple_' operations get a dentry reference on create/mkdir and drop
+	 * it on unlink/rmdir. So we have to get dentry reference here to
+	 * protect d_delete() from accessing a freed dentry.
+	 */
+	dget(dentry);
+	if (d_is_dir(dentry))
+		ret = simple_rmdir(dir, dentry);
+	else
+		ret = simple_unlink(dir, dentry);
+
+	if (!ret)
+		d_delete(dentry);
+	dput(dentry);
+
+	return ret;
+}
+EXPORT_SYMBOL(simple_remove);
+
 int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
 		  struct inode *new_dir, struct dentry *new_dentry,
 		  unsigned int flags)
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f7fdfe93e25d..74ea5f0b3b9d 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3245,6 +3245,7 @@ extern int simple_open(struct inode *inode, struct file *file);
 extern int simple_link(struct dentry *, struct inode *, struct dentry *);
 extern int simple_unlink(struct inode *, struct dentry *);
 extern int simple_rmdir(struct inode *, struct dentry *);
+extern int simple_remove(struct inode *, struct dentry *);
 extern int simple_rename(struct inode *, struct dentry *,
 			 struct inode *, struct dentry *, unsigned int);
 extern int noop_fsync(struct file *, loff_t, loff_t, int);
-- 
2.17.1

