[PATCH] add list_del_head function

[PATCH] add list_del_head function

[Tobias DiPasquale]

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Hi all,

I was working with some queues the other day and I noticed that there
was a list_add_tail() function in list.h, but no list_del_head()
function. This struck me as a little odd, so I went ahead and
implemented one in order to complete full queue functionality. The
patch below was generated against pristine 2.6.9 kernel.org kernel
sources and is attached to this email.

Please CC me on any replies, as I'm not subscribed to LKML. Thanks :)

Name: Add list_del_head for full queue functionality
Status: Tested
Signed-off-by: Tobias DiPasquale <codeslinger@gmail.com>

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[ Tobias DiPasquale ]
0x636f6465736c696e67657240676d61696c2e636f6d

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diff -Nrup linux-2.6.9/include/linux/list.h linux/include/linux/list.h
--- linux-2.6.9/include/linux/list.h	2004-10-18 21:54:31.000000000 +0000
+++ linux/include/linux/list.h	2004-11-20 18:55:12.373654048 +0000
@@ -166,6 +166,21 @@ static inline void list_del(struct list_
 }
 
 /**
+ * list_del_head - deletes first entry from list.
+ * @entry: return parameter; will contain former head of list on return.
+ * @head: head of list from which to delete.
+ *
+ * This function is useful for implementing queues. Caller must ensure
+ * the list is not empty before calling this function. On return, entry
+ * will point to the former head of the list.
+ */
+static inline void list_del_head(struct list_head **entry, struct list_head *head)
+{
+	*entry = head->next;
+	list_del(head->next);
+}
+
+/**
  * list_del_rcu - deletes entry from list without re-initialization
  * @entry: the element to delete from the list.
  *

Re: [PATCH] add list_del_head function

[Jens Axboe]

On Sat, Nov 20 2004, Tobias DiPasquale wrote:
> Hi all,
> 
> I was working with some queues the other day and I noticed that there
> was a list_add_tail() function in list.h, but no list_del_head()
> function. This struck me as a little odd, so I went ahead and
> implemented one in order to complete full queue functionality. The
> patch below was generated against pristine 2.6.9 kernel.org kernel
> sources and is attached to this email.

Generally patches like this have little merrit unless accompanied by
another patch converting several obvious pieces of kernel code to use
it.

Also I find the interface awkward and different from the other list
functions.

	entry = list_del_head(list);

would have been much nicer.

-- 
Jens Axboe

Re: [PATCH] add list_del_head function

[Tobias DiPasquale]

On Mon, 22 Nov 2004 10:20:59 +0100, Jens Axboe <axboe@suse.de> wrote: 
> Generally patches like this have little merrit unless accompanied by
> another patch converting several obvious pieces of kernel code to use
> it.
> 
> Also I find the interface awkward and different from the other list
> functions.
> 
>         entry = list_del_head(list);
> 
> would have been much nicer.

Ok I'll do both things and resubmit. Thanks for getting back to me :)

-- 
[ Tobias DiPasquale ]
0x636f6465736c696e67657240676d61696c2e636f6d