[PATCH 2/4] vfs: allow exclusive freezing of filesystems

["Darrick J. Wong" <djwong@xxxxxxxxxx>]

From: Darrick J. Wong <djwong@xxxxxxxxxx>

Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx>
---
 fs/super.c         |   33 +++++++++++++++++++++++++++++++++
 include/linux/fs.h |    2 ++
 2 files changed, 35 insertions(+)


diff --git a/fs/super.c b/fs/super.c
index 01891f9e6d5e..46abd21f94ac 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1762,6 +1762,24 @@ int freeze_super(struct super_block *sb)
 }
 EXPORT_SYMBOL(freeze_super);
 
+/**
+ * freeze_super_excl - lock the filesystem exclusively and force it into a
+ * consistent state.
+ * @sb: the super to lock
+ * @cookie: magic cookie to associate with this freeze so that only the caller
+ * can thaw the filesystem
+ *
+ * Syncs the super to make sure the filesystem is consistent and calls the fs's
+ * freeze_fs.  Subsequent calls to this without first thawing the fs will
+ * return -EBUSY.  The filesystem must not already be frozen, and can only be
+ * thawed by passing the same cookie to thaw_super_excl.
+ */
+int freeze_super_excl(struct super_block *sb, unsigned long cookie)
+{
+	return __freeze_super(sb, cookie);
+}
+EXPORT_SYMBOL(freeze_super_excl);
+
 static int thaw_super_locked(struct super_block *sb, unsigned long cookie)
 {
 	int error;
@@ -1813,6 +1831,21 @@ int thaw_super(struct super_block *sb)
 }
 EXPORT_SYMBOL(thaw_super);
 
+/**
+ * thaw_super_excl -- unfreeze filesystem
+ * @sb: the super to thaw
+ * @cookie: magic cookie passed to freeze_super_excl
+ *
+ * Releases an exclusive freeze on a filesystem and marks it writeable again
+ * after freeze_super().
+ */
+int thaw_super_excl(struct super_block *sb, unsigned long cookie)
+{
+	down_write(&sb->s_umount);
+	return thaw_super_locked(sb, cookie);
+}
+EXPORT_SYMBOL(thaw_super_excl);
+
 /*
  * Create workqueue for deferred direct IO completions. We allocate the
  * workqueue when it's first needed. This avoids creating workqueue for
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 800772361b1e..3a65bcc45f67 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2272,6 +2272,8 @@ extern int user_statfs(const char __user *, struct kstatfs *);
 extern int fd_statfs(int, struct kstatfs *);
 extern int freeze_super(struct super_block *super);
 extern int thaw_super(struct super_block *super);
+extern int freeze_super_excl(struct super_block *super, unsigned long cookie);
+extern int thaw_super_excl(struct super_block *super, unsigned long cookie);
 extern __printf(2, 3)
 int super_setup_bdi_name(struct super_block *sb, char *fmt, ...);
 extern int super_setup_bdi(struct super_block *sb);