[PATCH v3 2/4] ovl: split ovl_want_write() into two helpers

[Amir Goldstein <amir73il@gmail.com>]

ovl_get_mnt_write() gets write access to upper mnt without taking freeze
protection on upper sb and ovl_start_write() only takes freeze
protection on upper sb.

These helpers will be used to breakup the large ovl_want_write() scope
during copy up into finer grained freeze protection scopes.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/overlayfs/overlayfs.h |  4 ++++
 fs/overlayfs/util.c      | 26 ++++++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 72f57d919aa9..6da49bf78b90 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -398,7 +398,11 @@ static inline bool ovl_open_flags_need_copy_up(int flags)
 }
 
 /* util.c */
+int ovl_get_mnt_write(struct dentry *dentry);
+void ovl_start_write(struct dentry *dentry);
 int ovl_want_write(struct dentry *dentry);
+void ovl_put_mnt_write(struct dentry *dentry);
+void ovl_end_write(struct dentry *dentry);
 void ovl_drop_write(struct dentry *dentry);
 struct dentry *ovl_workdir(struct dentry *dentry);
 const struct cred *ovl_override_creds(struct super_block *sb);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 753734c55647..980e128ba0a4 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -17,12 +17,38 @@
 #include <linux/ratelimit.h>
 #include "overlayfs.h"
 
+/* Get write access to upper mnt - may fail if upper sb was remounted ro */
+int ovl_get_mnt_write(struct dentry *dentry)
+{
+	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
+	return __mnt_want_write(ovl_upper_mnt(ofs));
+}
+
+/* Get write access to upper sb - may block if upper sb is frozen */
+void ovl_start_write(struct dentry *dentry)
+{
+	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
+	sb_start_write(ovl_upper_mnt(ofs)->mnt_sb);
+}
+
 int ovl_want_write(struct dentry *dentry)
 {
 	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
 	return mnt_want_write(ovl_upper_mnt(ofs));
 }
 
+void ovl_put_mnt_write(struct dentry *dentry)
+{
+	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
+	__mnt_drop_write(ovl_upper_mnt(ofs));
+}
+
+void ovl_end_write(struct dentry *dentry)
+{
+	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
+	sb_end_write(ovl_upper_mnt(ofs)->mnt_sb);
+}
+
 void ovl_drop_write(struct dentry *dentry)
 {
 	struct ovl_fs *ofs = OVL_FS(dentry->d_sb);
-- 
2.34.1