ovl: warn instead of error if d_type is not supported

ovl: warn instead of error if d_type is not supported

commit e7c0b5991dd1be7b6f6dc2b54a15a0f47b64b007 upstream.

overlay needs underlying fs to support d_type. Recently I put in a
patch in to detect this condition and started failing mount if
underlying fs did not support d_type.

But this breaks existing configurations over kernel upgrade. Those who
are running docker (partially broken configuration) with xfs not
supporting d_type, are surprised that after kernel upgrade docker does
not run anymore.

https://github.com/docker/docker/issues/22937#issuecomment-229881315

So instead of erroring out, detect broken configuration and warn
about it. This should allow existing docker setups to continue
working after kernel upgrade.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 45aebeaf4f67 ("ovl: Ensure upper filesystem supports d_type")
Cc: <stable@vger.kernel.org> 4.6
Signed-off-by: SZ Lin (林上智) <sz.lin@moxa.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[sw0312.kim: cherry-pick linux-4.4.y commit 7eaa995c75bd to fix smack deny issue on overlayfs]
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Change-Id: I00157d6950ea475852a59259ff2dbd9cb06c9837