On 05-01-2012 05:57, Sakari Ailus wrote: > On Thu, Jan 05, 2012 at 10:52:02AM +0800, Scott Jiang wrote: >> 2012/1/4 Sakari Ailus <sakari.ailus@xxxxxx>: >>> Hi Scott, >>> >>> Thanks for the patch. >>> >>> On Wed, Dec 21, 2011 at 10:30:54AM -0500, Scott Jiang wrote: >>>> list_is_singular accepts a list head to test whether a list has just one entry. >>>> fh->list is the entry, fh->vdev->fh_list is the list head. >>>> >>>> Signed-off-by: Scott Jiang <scott.jiang.linux@xxxxxxxxx> >>>> --- >>>> drivers/media/video/v4l2-fh.c | 2 +- >>>> 1 files changed, 1 insertions(+), 1 deletions(-) >>>> >>>> diff --git a/drivers/media/video/v4l2-fh.c b/drivers/media/video/v4l2-fh.c >>>> index 9e3fc04..8292c4a 100644 >>>> --- a/drivers/media/video/v4l2-fh.c >>>> +++ b/drivers/media/video/v4l2-fh.c >>>> @@ -113,7 +113,7 @@ int v4l2_fh_is_singular(struct v4l2_fh *fh) >>>> if (fh == NULL || fh->vdev == NULL) >>>> return 0; >>>> spin_lock_irqsave(&fh->vdev->fh_lock, flags); >>>> - is_singular = list_is_singular(&fh->list); >>>> + is_singular = list_is_singular(&fh->vdev->fh_list); >>>> spin_unlock_irqrestore(&fh->vdev->fh_lock, flags); >>>> return is_singular; >>>> } >>> >>> Is there an issue that this patch resolves, or am I missing something? As >>> far as I can see, the list_is_singular() test returns the same result >>> whether you are testing a list item which is part of the list, or its head >>> in struct video_device. >>> >> Yes, the result is the same. But I don't think it's a good example >> because it may abuse this api. >> Can anybody figure out what this api needs you to pass in? I confess >> I am not sure about that. > > That's true; it's more correct (and intuitive as well) to use the real list > head for the purpose. But if the implementation really changed I bet a huge > number of other things would break as well. > > Acked-by: Sakari Ailus <sakari.ailus@xxxxxx> > > Hans: you wrote the patch adding this code (dfddb244); what do you think? All those list functions can operate on any node of the list, since the list is circular. So, there's not a real "head" for the list. The function implementation shows that: static inline void INIT_LIST_HEAD(struct list_head *list) { list->next = list; list->prev = list; } ... static inline int list_is_singular(const struct list_head *head) { return !list_empty(head) && (head->next == head->prev); } So, I prefer to not change it, _unless_ for some reason, you hit a bug on it (for example, by not having one of the list pointers filled). Regards, Mauro > > Regards, > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html