I'd prefer some variation on:

    int samedirfile( Dir *a, Dir *b )
    {
            if( a == b )
                    return 1;
    
            return  ( a && b ) &&
                    ( a->qid.type == b->qid.type ) &&
                    ( a->qid.path == b->qid.path ) &&
                    ( a->qid.vers == b->qid.vers ) &&
                    ( a->dev      == b->dev ) &&
                    ( a->type     == b->type );
    }
    
    ...
    
    if( samedirfile( a, b ) ) {
            fprint(2, "cp: %s and %s are the same file\n", an, bn);
            ret = 1;
    }

I think it's fascinating that we prefer styles that are almost opposites:

    int samedirfile(Dir *a, Dir *b) {
        if(a == b) {
            return 1;
        }

        return (a && b)
            && (a->qid.type == b->qid.type)
            && (a->qid.path == b->qid.path)
            && (a->qid.vers == b->qid.vers)
            && (a->dev == b->dev)
            && (a->type == b->type);
    }
    
    ...
    
    if(samedirfile(a, b)) {
        fprint(2, "cp: %s and %s are the same file\n", an, bn);
        ret = 1;
    }

I'll note I actually have a slight preference for prepended continuation operators like you have, but I stick to the style used at work for the sake of my sanity in trying to write consistent code.

I'm so, so, so glad that new languages are banning braceless if/else bodies.

So how about that python? </trololololo>

I should have of course said "some" :)