[PATCH] vfs: return EOPNOTSUPP when ioctl_fsthaw() is not supported

[Sami Kerola <kerolasa@iki.fi>]

An attempt to freeze a filesystem that does not support such operation is
reported as EOPNOTSUPP to user.  Running unfreeze to the same filesystem
returns EINVAL.  Later is a little misleading, users can mix that message
with return value from unfreezing when filesystem is not frozen.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>
---
 fs/ioctl.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ioctl.c b/fs/ioctl.c
index cb9b02940805..1d6372ef4008 100644
--- a/fs/ioctl.c
+++ b/fs/ioctl.c
@@ -566,6 +566,10 @@ static int ioctl_fsthaw(struct file *filp)
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
+	/* If filesystem doesn't support thaw feature, return. */
+	if (!sb->s_op->unfreeze_fs)
+		return -EOPNOTSUPP;
+
 	/* Thaw */
 	if (sb->s_op->thaw_super)
 		return sb->s_op->thaw_super(sb);
-- 
2.11.0