From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1L4hm6-0001a3-9o for qemu-devel@nongnu.org; Mon, 24 Nov 2008 15:11:14 -0500 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1L4hm5-0001Zr-RV for qemu-devel@nongnu.org; Mon, 24 Nov 2008 15:11:14 -0500 Received: from [199.232.76.173] (port=44437 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1L4hm5-0001Zo-Cb for qemu-devel@nongnu.org; Mon, 24 Nov 2008 15:11:13 -0500 Received: from mx2.redhat.com ([66.187.237.31]:59389) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1L4hm4-0000Aw-Sa for qemu-devel@nongnu.org; Mon, 24 Nov 2008 15:11:13 -0500 Received: from int-mx2.corp.redhat.com (int-mx2.corp.redhat.com [172.16.27.26]) by mx2.redhat.com (8.13.8/8.13.8) with ESMTP id mAOKBC8T005288 for ; Mon, 24 Nov 2008 15:11:12 -0500 Received: from ns3.rdu.redhat.com (ns3.rdu.redhat.com [10.11.255.199]) by int-mx2.corp.redhat.com (8.13.1/8.13.1) with ESMTP id mAOKBBSh030332 for ; Mon, 24 Nov 2008 15:11:11 -0500 Received: from dhcp-1-237.tlv.redhat.com (dhcp-1-237.tlv.redhat.com [10.35.1.237]) by ns3.rdu.redhat.com (8.13.8/8.13.8) with ESMTP id mAOKBA5L002479 for ; Mon, 24 Nov 2008 15:11:11 -0500 Date: Mon, 24 Nov 2008 22:11:29 +0200 From: Gleb Natapov Subject: Re: [Qemu-devel] [PATCH 3/5] Write table offset and size in one syscall. Message-ID: <20081124201129.GD3482@redhat.com> References: <20081123145248.22178.36228.stgit@dhcp-1-237.tlv.redhat.com> <20081123145312.22178.68255.stgit@dhcp-1-237.tlv.redhat.com> <492AD970.9050805@codemonkey.ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <492AD970.9050805@codemonkey.ws> Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org On Mon, Nov 24, 2008 at 10:42:24AM -0600, Anthony Liguori wrote: >> new_l1_size = s->l1_size; >> if (min_size <= new_l1_size) >> @@ -460,14 +459,12 @@ static int grow_l1_table(BlockDriverState *bs, int min_size) >> new_l1_table[i] = be64_to_cpu(new_l1_table[i]); >> /* set new table */ >> - data64 = cpu_to_be64(new_l1_table_offset); >> - if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_table_offset), >> - &data64, sizeof(data64)) != sizeof(data64)) >> - goto fail; >> - data32 = cpu_to_be32(new_l1_size); >> - if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_size), >> - &data32, sizeof(data32)) != sizeof(data32)) >> + *(uint32_t*)data = cpu_to_be32(new_l1_size); >> + *(uint64_t*)&data[4] = cpu_to_be64(new_l1_table_offset); >> + if (bdrv_pwrite(s->hd, offsetof(QCowHeader, l1_size), data, >> + sizeof(data)) != sizeof(data)) >> goto fail; >> >> > > Why not just introduces a uint8_t data[12] in this function, memcpy to > the right offsets, and do one brdv_pwrite? Then you don't need to do > weird things with packing. > It is exactly what I did except memcpy part. What can go wrong with packing the way I did it? >> be64_to_cpus(&new_table[i]); >> - data64 = cpu_to_be64(table_offset); >> + *(uint64_t*)data = cpu_to_be64(table_offset); >> + *(uint32_t*)&data[8] = cpu_to_be32(refcount_table_clusters); >> if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_offset), >> - &data64, sizeof(data64)) != sizeof(data64)) >> - goto fail; >> - data32 = cpu_to_be32(refcount_table_clusters); >> - if (bdrv_pwrite(s->hd, offsetof(QCowHeader, refcount_table_clusters), >> - &data32, sizeof(data32)) != sizeof(data32)) >> + data, sizeof(data)) != sizeof(data)) >> goto fail; >> > > Same here. Alternatively, you could use the cpu_to_beXXs() variants and > just pass in pointer offsets. > That is good idea. I'll use cpu_to_beXXs(). -- Gleb.