From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48311) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Xgv5S-0003hL-EU for qemu-devel@nongnu.org; Wed, 22 Oct 2014 08:32:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Xgv5N-000530-KR for qemu-devel@nongnu.org; Wed, 22 Oct 2014 08:32:22 -0400 Message-ID: <5447A3C0.6070003@redhat.com> Date: Wed, 22 Oct 2014 14:32:00 +0200 From: Max Reitz MIME-Version: 1.0 References: <201410221945053926307@sangfor.com> <54479C3E.1070803@huawei.com> <54479C8A.9000407@redhat.com> <54479CE5.7040406@redhat.com> <5447A151.2050000@huawei.com> <5447A1E1.7030102@redhat.com> <5447A374.4070309@huawei.com> In-Reply-To: <5447A374.4070309@huawei.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v4] snapshot: use local variable to bdrv_pwrite_sync L1 table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gonglei Cc: qemu-trivial , Kevin Wolf , Zhang Haoyu , qemu-devel , Stefan Hajnoczi On 2014-10-22 at 14:30, Gonglei wrote: > On 2014/10/22 20:24, Max Reitz wrote: > >> On 2014-10-22 at 14:21, Gonglei wrote: >>> On 2014/10/22 20:02, Max Reitz wrote: >>> >>>> On 2014-10-22 at 14:01, Max Reitz wrote: >>>>> On 2014-10-22 at 13:59, Gonglei wrote: >>>>>> On 2014/10/22 19:45, Zhang Haoyu wrote: >>>>>> >>>>>>> Use local variable to bdrv_pwrite_sync L1 table, >>>>>>> needless to make conversion of cached L1 table between >>>>>>> big-endian and host style. >>>>>>> >>>>>>> Signed-off-by: Zhang Haoyu >>>>>>> Reviewed-by: Max Reitz >>>>>>> --- >>>>>>> v3 -> v4: >>>>>>> - convert local L1 table to host-style before copy it >>>>>>> back to s->l1_table >>>>>>> >>>>>>> v2 -> v3: >>>>>>> - replace g_try_malloc0 with qemu_try_blockalign >>>>>>> - copy the latest local L1 table back to s->l1_table >>>>>>> after successfully bdrv_pwrite_sync L1 table >>>>>>> >>>>>>> v1 -> v2: >>>>>>> - remove the superflous assignment, l1_table = NULL; >>>>>>> - replace 512 with BDRV_SECTOR_SIZE, and align_offset with ROUND_UP >>>>>>> - remove needless check of if (l1_table) before g_free(l1_table) >>>>>>> >>>>>>> block/qcow2-refcount.c | 28 ++++++++++++---------------- >>>>>>> 1 file changed, 12 insertions(+), 16 deletions(-) >>>>>>> >>>>>>> diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c >>>>>>> index 2bcaaf9..3e4050a 100644 >>>>>>> --- a/block/qcow2-refcount.c >>>>>>> +++ b/block/qcow2-refcount.c >>>>>>> @@ -881,14 +881,17 @@ int >>>>>>> qcow2_update_snapshot_refcount(BlockDriverState *bs, >>>>>>> { >>>>>>> BDRVQcowState *s = bs->opaque; >>>>>>> uint64_t *l1_table, *l2_table, l2_offset, offset, l1_size2; >>>>>>> - bool l1_allocated = false; >>>>>>> int64_t old_offset, old_l2_offset; >>>>>>> int i, j, l1_modified = 0, nb_csectors, refcount; >>>>>>> int ret; >>>>>>> l2_table = NULL; >>>>>>> - l1_table = NULL; >>>>>>> l1_size2 = l1_size * sizeof(uint64_t); >>>>>>> + l1_table = qemu_try_blockalign(bs->file, l1_size2); >>>>>>> + if (l1_size2 && l1_table == NULL) { >>>>>> I think this check has a logic problem. If l1_size2 != 0 and >>>>>> l1_table == NULL, >>>>>> What will happen? >>>>> Then this condition is met and you return with -ENOMEM...? >>>> Oh, but I see something different: qemu_try_blockalign() never returns >>>> NULL, not even when you request 0 bytes. >>> Yes. But if l1_size2 is zero, will waste memory or some other problems. >>> Please see below: >>> >>> the original code: >>> l1_table = g_try_malloc0(align_offset(0, 512)); >>> -> l1_table = g_try_malloc0(0) >>> so l1_table == NULL. >>> >>> after this patch: >>> l1_table = qemu_try_blockalign(bs->file, 0) >>> l1_table will not be NULL. >> Okay, so you meant "if l1_size2 == 0 and l1_table != NULL". >> > Hum, sorry for my typo ;) > >>> I don't know whether l1_size2 can be zero or not. >> Probably not, but if it cannot be zero, testing for that case makes even >> less sense. >> > So, can we add a check at the begin of this function? We can just omit the "l1_size2 && " from the "if (l1_size2 && l1_table == NULL)". Max