Re: [Qemu-devel] [PATCH v4] snapshot: use local variable to bdrv_pwrite_syncL1 table

[Zhang Haoyu]

>> 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?
>
If the condition of "if (l1_size2 && l1_table == NULL)" is true,
below code will be performed,
s->cache_discards = false;
qcow2_process_discards(bs, ret);
g_free(l1_table);

What's your question?

Thanks,
Zhang Haoyu
>Best regards,
>-Gonglei
>
>> +        ret = -ENOMEM;
>> +        goto fail;
>> +    }
>>  
>>      s->cache_discards = true;
>>  
>> @@ -896,13 +899,6 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>>       * l1_table_offset when it is the current s->l1_table_offset! Be careful
>>       * when changing this! */
>>      if (l1_table_offset != s->l1_table_offset) {
>> -        l1_table = g_try_malloc0(align_offset(l1_size2, 512));
>> -        if (l1_size2 && l1_table == NULL) {
>> -            ret = -ENOMEM;
>> -            goto fail;
>> -        }
>> -        l1_allocated = true;
>> -
>>          ret = bdrv_pread(bs->file, l1_table_offset, l1_table, l1_size2);
>>          if (ret < 0) {
>>              goto fail;
>> @@ -912,8 +908,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
>>              be64_to_cpus(&l1_table[i]);
>>      } else {
>>          assert(l1_size == s->l1_size);
>> -        l1_table = s->l1_table;
>> -        l1_allocated = false;
>> +        memcpy(l1_table, s->l1_table, l1_size2);
>>      }
>>  
>>      for(i = 0; i < l1_size; i++) {
>> @@ -1055,13 +1050,14 @@ fail:
>>          }
>>  
>>          ret = bdrv_pwrite_sync(bs->file, l1_table_offset, l1_table, 
>> l1_size2);
>> -
>> -        for (i = 0; i < l1_size; i++) {
>> -            be64_to_cpus(&l1_table[i]);
>> +        if (ret == 0) {
>> +            for (i = 0; i < l1_size; i++) {
>> +                be64_to_cpus(&l1_table[i]);
>> +            }
>> +            memcpy(s->l1_table, l1_table, l1_size2);
>>          }
>>      }
>> -    if (l1_allocated)
>> -        g_free(l1_table);
>> +    g_free(l1_table);
>>      return ret;
>>  }
>>