On Tue, Mar 19, 2013 at 8:50 PM, Victor Buciuc <victor.buciuc@gmail.com> wrote:

On Tue, Mar 19, 2013 at 5:34 PM, Arlie Stephens <arlie@worldash.org> wrote:

...

Hi Folks,

I'm trying to understand the linux way of doing things, so as to write code which will be easier for experienced linux kernel people to understand. Yesterday I wound up in a 3 engineer discussion about something conceptually simple, that just didn't want to be done with the tools at hand; what's worse, the only ways I could see to do it were (a) do my own linked lists or (b) write some routines that relied kind of heavily on the never-mentioned-in-documentation details of linux/list.h I'll probably go with option (b), as that seems less insane, but I thought I might as well ask here as well.

Here's the problem. I have a collection of resources. Call them A,B,C,D but note that resources get added at run time, so I don't know how many to expect. I want to go through them in a round robin fashion, but not all at once. On the first request, I use A. On a later request I use B, etc. This seems to me to map naturally to a circular linked list, with a "cursor" - a pointer of some kind to the next one I want to use. To make my specific situation more interesting, I actually have multiple cursors - that may or may not happen to point to the same node at any given time, but usually will not.

This is where I wish I could draw pictures in ascii emails ;-) Perhaps the following will come through halfway sanely:

C1 C2 C3 V / V A<->B<->C-<->D ^------------^

Hi,

Another option might be to not iterate through the list but to simply move the element you're processing to the end of the list using list_rotate_left[1]. And you could use list_next_entry[2] to get the next entry after the head. You'll have to check that the list is empty, tough.

This would cost you some extra operations but you'll use the existing interface.

[1] http://lxr.linux.no/linux+v3.8.3/include/linux/list.h#L214 [2] http://lxr.linux.no/linux+v3.8.3/include/linux/list.h#L361

Regards, Victor Buciuc.

Forgot to send to the list. Regards, Victor Buciuc.