list_merge behaves like list_splice, except it can be used with
headless lists. that is, the resulting list will have @head
immediately preceeding @list.
This is used by the contig list feature in the Elevator I/O scheduler
Signed-off-by: Nate Diller <[email protected]>
---
list.h | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
---
diff -urpN -X dontdiff linux-2.6.18-rc1-mm2/include/linux/list.h
linux-dput/include/linux/list.h
--- linux-2.6.18-rc1-mm2/include/linux/list.h 2006-07-18
15:00:53.000000000 -0700
+++ linux-dput/include/linux/list.h 2006-08-03 18:42:00.000000000 -0700
@@ -357,6 +357,27 @@ static inline void list_splice_init(stru
}
}
+/**
+ * list_merge - merge two headless lists
+ * @list: the new list to merge.
+ * @head: the place to add it in the first list.
+ *
+ * This is similar to list_splice(), except it merges every item onto @list,
+ * not excluding @head itself. It is a noop if @head already immediately
+ * preceeds @list.
+ */
+static inline void list_merge(struct list_head *list, struct list_head *head)
+{
+ struct list_head *last = list->prev;
+ struct list_head *at = head->next;
+
+ list->prev = head;
+ head->next = list;
+
+ last->next = at;
+ at->prev = last;
+}
+
/**
* list_entry - get the struct for this entry
* @ptr: the &struct list_head pointer.
On Thu, 3 Aug 2006 19:15:15 -0700
"Nate Diller" <[email protected]> wrote:
> +/**
> + * list_merge - merge two headless lists
> + * @list: the new list to merge.
> + * @head: the place to add it in the first list.
> + *
> + * This is similar to list_splice(), except it merges every item onto @list,
> + * not excluding @head itself. It is a noop if @head already immediately
> + * preceeds @list.
"precedes"
> + */
> +static inline void list_merge(struct list_head *list, struct list_head *head)
> +{
> + struct list_head *last = list->prev;
> + struct list_head *at = head->next;
> +
> + list->prev = head;
> + head->next = list;
> +
> + last->next = at;
> + at->prev = last;
> +}
Interesting. I didn't realise that none of the existing functions could do
this. I wonder if we can flesh the comment out a bit: define "headless" a
little more verbosely.
Should we call it list_splice_headless() or something? list_merge is a bit
vague.
"Nate Diller" <[email protected]> writes:
> + * This is similar to list_splice(), except it merges every item onto @list,
> + * not excluding @head itself. It is a noop if @head already immediately
> + * preceeds @list.
"not excluding"? Is that the same as "including"?
--
Ben Pfaff
email: [email protected]
web: http://benpfaff.org
On Thu, 3 Aug 2006, Andrew Morton wrote:
> On Thu, 3 Aug 2006 19:15:15 -0700
> "Nate Diller" <[email protected]> wrote:
>
> > +/**
> > + * list_merge - merge two headless lists
> > + * @list: the new list to merge.
> > + * @head: the place to add it in the first list.
> > + *
> > + * This is similar to list_splice(), except it merges every item onto @list,
> > + * not excluding @head itself. It is a noop if @head already immediately
> > + * preceeds @list.
>
> "precedes"
>
> > + */
> > +static inline void list_merge(struct list_head *list, struct list_head *head)
> > +{
> > + struct list_head *last = list->prev;
> > + struct list_head *at = head->next;
> > +
> > + list->prev = head;
> > + head->next = list;
> > +
> > + last->next = at;
> > + at->prev = last;
> > +}
>
> Interesting. I didn't realise that none of the existing functions could do
> this. I wonder if we can flesh the comment out a bit: define "headless" a
> little more verbosely.
>
> Should we call it list_splice_headless() or something? list_merge is a bit
> vague.
>
Yes, please do explicitly mention headless. I could see someone using
this for something with a head and causing some strange bugs.
Also, it might be a good idea to get rid of the "head" in the parameter.
Perhaps call it "start" or something else. It's a little confusing to
have a headless list operation that calls the start of a list "head".
-- Steve