From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38499) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bwB6b-0002oE-5N for qemu-devel@nongnu.org; Mon, 17 Oct 2016 12:49:42 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bwB6W-0001IK-Bc for qemu-devel@nongnu.org; Mon, 17 Oct 2016 12:49:41 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38173) by eggs.gnu.org with esmtps (TLS1.0:RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1bwB6W-0001HX-4V for qemu-devel@nongnu.org; Mon, 17 Oct 2016 12:49:36 -0400 Received: from pps.filterd (m0098393.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u9HGnGmc097373 for ; Mon, 17 Oct 2016 12:49:34 -0400 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0a-001b2d01.pphosted.com with ESMTP id 264ym9946m-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Mon, 17 Oct 2016 12:49:34 -0400 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 17 Oct 2016 12:49:33 -0400 References: <1476394254-7987-1-git-send-email-duanj@linux.vnet.ibm.com> <1476394254-7987-3-git-send-email-duanj@linux.vnet.ibm.com> <20161014104447.GC2030@work-vm> <4b63338c-cf70-ce4d-1854-afc23c38b88f@linux.vnet.ibm.com> <20161014170412.GE2030@work-vm> From: Jianjun Duan Date: Mon, 17 Oct 2016 09:49:23 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Message-Id: <2a8ea35b-8335-1132-002b-c45e891a57e4@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [Qemu-ppc] [QEMU PATCH v6 2/2] migration: migrate QTAILQ List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Halil Pasic , "Dr. David Alan Gilbert" Cc: veroniabahaa@gmail.com, peter.maydell@linaro.org, mdroth@linux.vnet.ibm.com, mst@redhat.com, quintela@redhat.com, mark.cave-ayland@ilande.co.uk, qemu-devel@nongnu.org, mreitz@redhat.com, blauwirbel@gmail.com, amit.shah@redhat.com, qemu-ppc@nongnu.org, kraxel@redhat.com, kwolf@redhat.com, dmitry@daynix.com, pbonzini@redhat.com, rth@twiddle.net, leon.alrae@imgtec.com, aurelien@aurel32.net, david@gibson.dropbear.id.au 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 >