Add limit to page size used by overlay2 driver

Go can falsely report a larger page size than supported,
causing overlay2 mount arguments to be truncated. When overlay2
detects the mount arguments have hit the page limit, it will
switch to using relative paths. If this limit is smaller than
the actual page size there is no behavioral problems, but if it
is larger mounts can fail for images with many layers.

Closes #27384

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

daemon/graphdriver/overlay2/overlay.go

@@ -473,6 +473,15 @@ func (d *Driver) Get(id string, mountLabel string) (s string, err error) {
 
 	pageSize := syscall.Getpagesize()
 
+	// Go can return a larger page size than supported by the system
+	// as of go 1.7. This will be fixed in 1.8 and this block can be
+	// removed when building with 1.8.
+	// See https://github.com/golang/go/commit/1b9499b06989d2831e5b156161d6c07642926ee1
+	// See https://github.com/docker/docker/issues/27384
+	if pageSize > 4096 {
+		pageSize = 4096
+	}
+
 	// Use relative paths and mountFrom when the mount data has exceeded
 	// the page size. The mount syscall fails if the mount data cannot
 	// fit within a page and relative links make the mount data much