Go: Don't grow sparse file too fast

APFS exhibits a weird behavior wrt sparse files: we cannot create (or
grow) them "too fast": there's a limit, apparently related to the
available disk space.  However, if the additional space is small
enough, we can procede way beyond the available disk space.  So grow
incrementally, by steps of 1GB.

More details available in docker/for-mac#2383.

Signed-off-by: Akim Demaille <akim.demaille@docker.com>

go/disk.go

@@ -223,7 +223,28 @@ func (d *RawDisk) getCurrentSize() (int, error) {
 
 // Resize the virtual size of the disk
 func (d *RawDisk) resize() error {
-	return os.Truncate(d.Path, int64(d.Size)*mib)
+	s, err := d.getCurrentSize()
+	if err != nil {
+		return fmt.Errorf("Cannot resize %q: %v", d, err)
+	}
+	log.Infof("Resize %q from %vMiB to %vMiB", d, s, d.GetSize())
+	// APFS exhibits a weird behavior wrt sparse files: we cannot
+	// create (or grow) them "too fast": there's a limit,
+	// apparently related to the available disk space.  However,
+	// if the additional space is small enough, we can procede way
+	// beyond the available disk space.  So grow incrementally,
+	// by steps of 1GB.
+	for s < d.Size {
+		s += 1000
+		if d.Size < s {
+			s = d.Size
+		}
+		if err := os.Truncate(d.Path, int64(s)*mib); err != nil {
+			return fmt.Errorf("Cannot resize %q to %vMiB: %v", d, s, err)
+		}
+	}
+	log.Infof("Resized %q to %vMiB", d, d.GetSize())
+	return nil
 }
 
 // Stop cleans up this disk when we are quitting.