[PATCH 3/5] fs: add mnt_want_write_trylock()

[Jens Axboe <axboe@kernel.dk>]

trylock variant of mnt_want_write() - this ends up being pretty trivial,
as we already have a trylock variant of the sb_start_write() helper.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/namespace.c        | 18 ++++++++++++++++++
 include/linux/mount.h |  1 +
 2 files changed, 19 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index cebaa3e81794..7881cb5595af 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -359,6 +359,24 @@ int mnt_want_write(struct vfsmount *m)
 }
 EXPORT_SYMBOL_GPL(mnt_want_write);
 
+/**
+ * mnt_want_write_trylock - try to get write access to a mount
+ * @m: the mount on which to take a write
+ *
+ * trylock variant of @mnt_want_write. See description above.
+ */
+int mnt_want_write_trylock(struct vfsmount *m)
+{
+	int ret;
+
+	if (!sb_start_write_trylock(m->mnt_sb))
+		return -EAGAIN;
+	ret = __mnt_want_write(m);
+	if (ret)
+		sb_end_write(m->mnt_sb);
+	return ret;
+}
+
 /**
  * mnt_clone_write - get write access to a mount
  * @mnt: the mount on which to take a write
diff --git a/include/linux/mount.h b/include/linux/mount.h
index aaf343b38671..e267e622d843 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -78,6 +78,7 @@ struct file; /* forward dec */
 struct path;
 
 extern int mnt_want_write(struct vfsmount *mnt);
+extern int mnt_want_write_trylock(struct vfsmount *mnt);
 extern int mnt_want_write_file(struct file *file);
 extern int mnt_clone_write(struct vfsmount *mnt);
 extern void mnt_drop_write(struct vfsmount *mnt);
-- 
2.29.2