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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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