Signed-off-by is like a legal document to say that you haven't added any proprietary SCO UNIXWARE code to the patch. You have sign every patch if you email it. Acked-by and Reviewed-by are less clear. Acked-by means you want it to be merged, I guess? I never use Acked by because I'm not a maintainer so it's not my place to approve things. regards, dan carpenter