[PATCH 1/2] fs: Add and export file_needs_remove_privs

[Bernd Schubert <bschubert@ddn.com>]

File systems want to hold a shared lock for DIO writes,
but may need to drop file priveliges - that a requires an
exclusive lock. The new export function file_needs_remove_privs()
is added in order to first check if that is needed.

Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Dharmendra Singh <dsingh@ddn.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Bernd Schubert <bschubert@ddn.com>
---
 fs/inode.c         | 8 ++++++++
 include/linux/fs.h | 1 +
 2 files changed, 9 insertions(+)

diff --git a/fs/inode.c b/fs/inode.c
index 67611a360031..9b05db602e41 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -2013,6 +2013,14 @@ int dentry_needs_remove_privs(struct mnt_idmap *idmap,
 	return mask;
 }
 
+int file_needs_remove_privs(struct file *file)
+{
+	struct dentry *dentry = file_dentry(file);
+
+	return dentry_needs_remove_privs(file_mnt_idmap(file), dentry);
+}
+EXPORT_SYMBOL_GPL(file_needs_remove_privs);
+
 static int __remove_privs(struct mnt_idmap *idmap,
 			  struct dentry *dentry, int kill)
 {
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 562f2623c9c9..9245f0de00bc 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2721,6 +2721,7 @@ extern struct inode *new_inode_pseudo(struct super_block *sb);
 extern struct inode *new_inode(struct super_block *sb);
 extern void free_inode_nonrcu(struct inode *inode);
 extern int setattr_should_drop_suidgid(struct mnt_idmap *, struct inode *);
+int file_needs_remove_privs(struct file *);
 extern int file_remove_privs(struct file *);
 int setattr_should_drop_sgid(struct mnt_idmap *idmap,
 			     const struct inode *inode);
-- 
2.39.2