gentoo-overlay/dev-util/strace/metadata.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE pkgmetadata SYSTEM "http://www.gentoo.org/dtd/metadata.dtd">
<pkgmetadata>
  <herd>base-system</herd>
  <use>
    <flag name="aio">
      Enable <pkg>dev-libs/libaio</pkg> support for tracing Asynchronous I/O operations
    </flag>
  </use>
</pkgmetadata>