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From: | Max Reitz |
Subject: | Re: [Qemu-devel] [PATCH v4] snapshot: use local variable to bdrv_pwrite_sync L1 table |
Date: | Wed, 22 Oct 2014 14:32:00 +0200 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
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 <address@hidden> Reviewed-by: Max Reitz <address@hidden> --- 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
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