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Date: Sat, 15 Mar 2008 23:36:36 +0100 From: Peter Zijlstra <a.p.zijlstra@...llo.nl> To: Masami Hiramatsu <mhiramat@...hat.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, ananth@...ibm.com, jkenisto@...ibm.com, linux-kernel@...r.kernel.org, systemtap@...rces.redhat.com, prasanna@...ibm.com, shaohua.li@...el.com, davem@...emloft.net, fche@...hat.com Subject: Re: [PATCH -mm 1/5] list.h: add list_singleton On Fri, 2008-03-14 at 18:22 -0400, Masami Hiramatsu wrote: > Andrew Morton wrote: > > If your usage pattern is: > > > > struct foo { > > ... > > struct list_head bar_list; /* A list of `struct bar's */ > > }; > > > > struct bar { > > struct list_head list; /* Attached to foo.bar_list */ > > ... > > }; > > > > then yes, list_singleton() makes sense. > > > > But in other usage patterns it does not: > > > > struct foo { > > struct bar *bar_list; > > ... > > }; > > > > struct bar { > > struct list_head list; /* All the other bars go here */ > > ... > > }; > > > > In the second case, emptiness is signified by foo.bar_list==NULL. And in > > this case, code which does > > > > if (foo->bar_list && list_singleton(&foo->bar_list->list)) > > > > will fail if there is a single item on the list! > > > > The second usage pattern is uncommon and list_empty() also returns > > misleading answers when list_heads are used this way. > > I agreed. I assume that list_singleton() is used like as list_empty(). > > > > So I guess we can proceed with your list_singleton(), but I'd just like to > > flag this possible confusion, see what people think.. May I kindly ask to please not use the singleton name like this. It does not implement the singleton pattern and will be a great confusion for everybody who expects it to. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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