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 <zhan...@sangfor.com> >>>> Reviewed-by: Max Reitz <mre...@redhat.com> >>>> --- >>>> 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. I don't know whether l1_size2 can be zero or not. Best regards, -Gonglei > Therefore, just "if (l1_table == NULL)" is sufficient. > > Max