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SubjectRe: [PATCH 1/4] list.h: Add list_splice_tail() and list_splice_tail_init()
On Wed, Aug 06, 2008 at 01:26:19PM -0700, Luis Rodriguez wrote:
> On Tue, Aug 05, 2008 at 02:03:15AM -0700, Peter Zijlstra wrote:
> > On Mon, 2008-08-04 at 15:48 -0700, Luis R. Rodriguez wrote:
> > > If you are using linked lists for queues list_splice() will not do what
> > > you would expect even if you use the elements passed reversed. We need
> > > to handle these differently. We add list_splice_tail() and
> > > list_splice_tail_init()
> >
> > In the -rt tree we have this:
> >
> > ---
> > rt: list_splice2
> >
> > Introduce list_splice2{,_tail}() which will splice a sub-list denoted
> > by two list items instead of the full list.
> >
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
>
> I like your version of list_splice_tail() and list_splice_tail_init()
> more as you re-use __list_splice() and fix it for its use instad of
> adding a new __list_splice_tail(). You also caught some users of
> __list_splice() for tail purposes. Its a good thing both versions
> are functionally equivalent :) otherwise one of us was doing something
> wrong.
>
> We just need to also clarify list_splice() is for stacks and not
> queues, I can add that. You patch however fails with checkpatch and
> forgot to add kdoc. I'll correct it.
>
> Last, list_splice2() should go in a separate patch and could use just a
> little bit more documentation as exactly what it does. Also the last
> hunk doesn't apply as 2.6.27 doesn't have lib/lock_list.c yet. To get ath9k
> in 2.6.27 we need list_splice_tail() and list_splice_tail_init(),
> how's this for 2.6.27:

Sorry, I forgot to add my kdoc for list_splice_tail_init(), here it is
with it added:
--
list.h: Add list_splice_tail() and list_splice_tail_init()

If you are using linked lists for queues list_splice() will not do what
you would expect even if you use the elements passed reversed. We need
to handle these differently. We add list_splice_tail() and
list_splice_tail_init().

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
---
drivers/dma/ioat_dma.c | 2 +-
drivers/usb/host/ehci-q.c | 2 +-
include/linux/list.h | 47 ++++++++++++++++++++++++++++++++++++--------
3 files changed, 40 insertions(+), 11 deletions(-)
diff --git a/drivers/dma/ioat_dma.c b/drivers/dma/ioat_dma.c
index a52156e..bc8c6e3 100644
--- a/drivers/dma/ioat_dma.c
+++ b/drivers/dma/ioat_dma.c
@@ -551,7 +551,7 @@ static dma_cookie_t ioat1_tx_submit(struct dma_async_tx_descriptor *tx)
/* write address into NextDescriptor field of last desc in chain */
to_ioat_desc(ioat_chan->used_desc.prev)->hw->next =
first->async_tx.phys;
- __list_splice(&new_chain, ioat_chan->used_desc.prev);
+ list_splice_tail(&new_chain, &ioat_chan->used_desc);

ioat_chan->dmacount += desc_count;
ioat_chan->pending += desc_count;
diff --git a/drivers/usb/host/ehci-q.c b/drivers/usb/host/ehci-q.c
index 2622b65..3712b92 100644
--- a/drivers/usb/host/ehci-q.c
+++ b/drivers/usb/host/ehci-q.c
@@ -932,7 +932,7 @@ static struct ehci_qh *qh_append_tds (

list_del (&qtd->qtd_list);
list_add (&dummy->qtd_list, qtd_list);
- __list_splice (qtd_list, qh->qtd_list.prev);
+ list_splice_tail(qtd_list, &qh->qtd_list);

ehci_qtd_init(ehci, qtd, qtd->qtd_dma);
qh->dummy = qtd;
diff --git a/include/linux/list.h b/include/linux/list.h
index 453916b..a886f27 100644
--- a/include/linux/list.h
+++ b/include/linux/list.h
@@ -215,21 +215,21 @@ static inline int list_is_singular(const struct list_head *head)
}

static inline void __list_splice(const struct list_head *list,
- struct list_head *head)
+ struct list_head *prev,
+ struct list_head *next)
{
struct list_head *first = list->next;
struct list_head *last = list->prev;
- struct list_head *at = head->next;

- first->prev = head;
- head->next = first;
+ first->prev = prev;
+ prev->next = first;

- last->next = at;
- at->prev = last;
+ last->next = next;
+ next->prev = last;
}

/**
- * list_splice - join two lists
+ * list_splice - join two lists, this is designed for stacks
* @list: the new list to add.
* @head: the place to add it in the first list.
*/
@@ -237,7 +237,19 @@ static inline void list_splice(const struct list_head *list,
struct list_head *head)
{
if (!list_empty(list))
- __list_splice(list, head);
+ __list_splice(list, head, head->next);
+}
+
+/**
+ * list_splice_tail - join two lists, each list being a queue
+ * @list: the new list to add.
+ * @head: the place to add it in the first list.
+ */
+static inline void list_splice_tail(struct list_head *list,
+ struct list_head *head)
+{
+ if (!list_empty(list))
+ __list_splice(list, head->prev, head);
}

/**
@@ -251,7 +263,24 @@ static inline void list_splice_init(struct list_head *list,
struct list_head *head)
{
if (!list_empty(list)) {
- __list_splice(list, head);
+ __list_splice(list, head, head->next);
+ INIT_LIST_HEAD(list);
+ }
+}
+
+/**
+ * list_splice_tail_init - join two lists, each list being a queue, and
+ * reinitialise the emptied list.
+ * @list: the new list to add.
+ * @head: the place to add it in the first list.
+ *
+ * The list at @list is reinitialised
+ */
+static inline void list_splice_tail_init(struct list_head *list,
+ struct list_head *head)
+{
+ if (!list_empty(list)) {
+ __list_splice(list, head->prev, head);
INIT_LIST_HEAD(list);
}
}
--
1.5.6.rc2.15.g457bb.dirty


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