On 10/15/2016 05:48 AM, Halil Pasic wrote: > > > On 10/14/2016 07:18 PM, Jianjun Duan wrote: >>>>>> +/* >>>>>>>>>> + * Offsets of layout of a tail queue head. >>>>>>>>>> + */ >>>>>>>>>> +#define QTAILQ_FIRST_OFFSET 0 >>>>>>>>>> +#define QTAILQ_LAST_OFFSET (sizeof(void *)) >>>>>>>>>> + >>>>>>>>>> +/* >>>>>>>>>> + * Offsets of layout of a tail queue element. >>>>>>>>>> + */ >>>>>>>>>> +#define QTAILQ_NEXT_OFFSET 0 >>>>>>>>>> +#define QTAILQ_PREV_OFFSET (sizeof(void *)) >>>>>>>>>> + >>>>>>>>>> +/* >>>>>>>>>> + * Tail queue tranversal using pointer arithmetic. >>>>>>>>>> + */ >>>>>>>>>> +#define QTAILQ_RAW_FOREACH(elm, head, entry) >>>>>>>>>> \ >>>>>>>>>> + for ((elm) = *((void **) ((char *) (head) + >>>>>>>>>> QTAILQ_FIRST_OFFSET)); \ >>>>>>>>>> + (elm); >>>>>>>>>> \ >>>>>>>>>> + (elm) = >>>>>>>>>> \ >>>>>>>>>> + *((void **) ((char *) (elm) + (entry) + >>>>>>>>>> QTAILQ_NEXT_OFFSET))) >>>>>>>>>> +/* >>>>>>>>>> + * Tail queue insertion using pointer arithmetic. >>>>>>>>>> + */ >>>>>>>>>> +#define QTAILQ_RAW_INSERT_TAIL(head, elm, entry) do { >>>>>>>>>> \ >>>>>>>>>> + *((void **) ((char *) (elm) + (entry) + >>>>>>>>>> QTAILQ_NEXT_OFFSET)) = NULL; \ >>>>>>>>>> + *((void **) ((char *) (elm) + (entry) + >>>>>>>>>> QTAILQ_PREV_OFFSET)) = \ >>>>>>>>>> + *((void **) ((char *) (head) + QTAILQ_LAST_OFFSET)); >>>>>>>>>> \ >>>>>>>>>> + **((void ***)((char *) (head) + QTAILQ_LAST_OFFSET)) = >>>>>>>>>> (elm); \ >>>>>>>>>> + *((void **) ((char *) (head) + QTAILQ_LAST_OFFSET)) = >>>>>>>>>> \ >>>>>>>>>> + (void *) ((char *) (elm) + (entry) + >>>>>>>>>> QTAILQ_NEXT_OFFSET); \ >>>>>>>>>> +} while (/*CONSTCOND*/0) >>>>>>>> >>>>>>>> I wonder if there's a simpler way to do this; I'm not sure this works, >>>>>>>> but something like: >>>>>>>> >>>>>>>> struct QTAILQDummy { >>>>>>>> char dummy; >>>>>>>> }; >>>>>>>> >>>>>>>> QTAILQ_HEAD(QTAILQRawHead, struct QTAILQDummy) >>>>>>>> typedef QTAILQ_ENTRY(struct QTAILQDummy) QTAILQRawEntry; >>>>>>>> >>>>>>>> #define QTAILQ_RAW_FOREACH(elm, head, entry) >>>>>>>> \ >>>>>>>> for ((elm) = ((struct QTAILQRawHead *)head)->tqh_first) >>>>>>>> \ >>>>>>>> (elm); >>>>>>>> \ >>>>>>>> (elm) = >>>>>>>> \ >>>>>>>> (elm) = ((QTAILQRawEntry *)((char *) (elm) + >>>>>>>> (entry)))->tqh_next >>>>>>>> >>>>>>>> and then I think elm gets declared as a struct QTAILQDummy. >>>>>>>> But it does avoid those >>>>>>>> FIRST_OFFSET/LAST_OFFSET/NEXT_OFFSET/PREV_OFFSET calculations. >>>>>>>> >>>>>>>> Would that work? >>>>>>>> >>>>>> It is intended for QTAILQ of any type. So type is not available. >>>> >>>> I think it might be possible to do it generally. >>>> >> If we have type, then we can use what is there already, and don't need a >> pointer arithmetic based approach. Inside put/get, we only get type >> layout info from vmsd, which is all about size and offset. This macro >> is used inside put/get, so I am not sure how we can directly use type >> here. >> > > Dave's approach seems perfectly sane to me. > > Jianjun have you actually tried to make it work before writing this? > Your argument does not work, because what you need from vmsd for > QTAILQ_RAW_FOREACH is only .start which corresponds to the entry > parameter of the macro. Dave still does the pointer arithmetic to > get a pointer (char*) to the anonymous struct holding tqe_next > and tqe_prev. Now since no arithmetic is done wit tqe_next > and tqe_prev, only dereferencing, their pointer type does not matter > all that much so we can do the and follow the pointer. Same goes > for the head. > > Actually the QTAILQDummy is not necessary in my opinion since we can > probably (did not try it out myself) do: > > Q_TAILQ_HEAD(QTAILQRawHead, void,) > typedef Q_TAILQ_ENTRY(void,) QTAILQRawEntry; >
Now I see. I thought Dave was using QTAILQDummy as an example. Thanks, Jianjun > Cheers, > Halil >