Re: [Qemu-devel] [PATCH alt 4/7] block/qcow2: Implement status CB for amend

[Max Reitz <mreitz@redhat.com>]

On 31.07.2014 10:06, Benoît Canet wrote:
> The Saturday 26 Jul 2014 à 21:22:08 (+0200), Max Reitz wrote :
>> The only really time-consuming operation potentially performed by
>> qcow2_amend_options() is zero cluster expansion when downgrading qcow2
>> images from compat=1.1 to compat=0.10, so report status of that
>> operation and that operation only through the status CB.
>>
>> For this, approximate the progress as the number of L1 entries visited
>> during the operation.
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   block/qcow2-cluster.c | 36 ++++++++++++++++++++++++++++++++----
>>   block/qcow2.c         |  9 ++++-----
>>   block/qcow2.h         |  3 ++-
>>   3 files changed, 38 insertions(+), 10 deletions(-)
>>
>> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
>> index 4208dc0..f8bec6f 100644
>> --- a/block/qcow2-cluster.c
>> +++ b/block/qcow2-cluster.c
>> @@ -1548,10 +1548,17 @@ fail:
>>    * zero expansion (i.e., has been filled with zeroes and is referenced from an
>>    * L2 table). nb_clusters contains the total cluster count of the image file,
>>    * i.e., the number of bits in expanded_clusters.
>> + *
>> + * l1_entries and *visited_l1_entries are ued to keep track of progress for
>> + * status_cb(). l1_entries contains the total number of L1 entries and
>> + * *visited_l1_entries counts all visited L1 entries.
>>    */
>>   static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
>>                                         int l1_size, uint8_t **expanded_clusters,
>> -                                      uint64_t *nb_clusters)
>> +                                      uint64_t *nb_clusters,
>> +                                      int64_t *visited_l1_entries,
>> +                                      int64_t l1_entries,
>> +                                      BlockDriverAmendStatusCB *status_cb)
>>   {
>>       BDRVQcowState *s = bs->opaque;
>>       bool is_active_l1 = (l1_table == s->l1_table);
>> @@ -1571,6 +1578,7 @@ static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
>>   
>>           if (!l2_offset) {
>>               /* unallocated */
>> +            (*visited_l1_entries)++;
>>               continue;
>>           }
>>   
>> @@ -1703,6 +1711,13 @@ static int expand_zero_clusters_in_l1(BlockDriverState *bs, uint64_t *l1_table,
>>                   }
>>               }
>>           }
>> +
>> +        (*visited_l1_entries)++;
>> +
>> +        if (status_cb) {
>> +            status_cb(bs, *visited_l1_entries << (s->l2_bits + s->cluster_bits),
>> +                      l1_entries << (s->l2_bits + s->cluster_bits));
> Shifting is a multiplication so it keep proportionality intact.
> So do we really need these shifts ?

As of patch 1, the variables are defined as "offset" and "working_size" 
which I meant to be byte ranges. We could indeed leave the unit for 
BlockDriverAmendStatusCB's parameters undefined (and leave it up to the 
block driver, only specifying that offset / working_size has to be the 
progress ratio), but then we could just as well just give a floating 
point percentage to that function.

Bytes as a unit seemed safe to me, however, since all of qemu's code 
assumes byte ranges to always fit in int64_t; and the reason I preferred 
them over a percentage is that block jobs use bytes as well.

A real reason not to use bytes would be that some driver is unable to 
give a "byte" representation of its workload during the amend progress; 
however, this seems unlikely to me (every large workload which should be 
part of the progress report should be somehow representable as bytes).

Max

>> +        }
>>       }
>>   
>>       ret = 0;
>> @@ -1729,21 +1744,32 @@ fail:
>>    * allocation for pre-allocated ones). This is important for downgrading to a
>>    * qcow2 version which doesn't yet support metadata zero clusters.
>>    */
>> -int qcow2_expand_zero_clusters(BlockDriverState *bs)
>> +int qcow2_expand_zero_clusters(BlockDriverState *bs,
>> +                               BlockDriverAmendStatusCB *status_cb)
>>   {
>>       BDRVQcowState *s = bs->opaque;
>>       uint64_t *l1_table = NULL;
>>       uint64_t nb_clusters;
>> +    int64_t l1_entries = 0, visited_l1_entries = 0;
>>       uint8_t *expanded_clusters;
>>       int ret;
>>       int i, j;
>>   
>> +    if (status_cb) {
>> +        l1_entries = s->l1_size;
>> +        for (i = 0; i < s->nb_snapshots; i++) {
>> +            l1_entries += s->snapshots[i].l1_size;
>> +        }
>> +    }
>> +
>>       nb_clusters = size_to_clusters(s, bs->file->total_sectors *
>>                                      BDRV_SECTOR_SIZE);
>>       expanded_clusters = g_malloc0((nb_clusters + 7) / 8);
>>   
>>       ret = expand_zero_clusters_in_l1(bs, s->l1_table, s->l1_size,
>> -                                     &expanded_clusters, &nb_clusters);
>> +                                     &expanded_clusters, &nb_clusters,
>> +                                     &visited_l1_entries, l1_entries,
>> +                                     status_cb);
>>       if (ret < 0) {
>>           goto fail;
>>       }
>> @@ -1777,7 +1803,9 @@ int qcow2_expand_zero_clusters(BlockDriverState *bs)
>>           }
>>   
>>           ret = expand_zero_clusters_in_l1(bs, l1_table, s->snapshots[i].l1_size,
>> -                                         &expanded_clusters, &nb_clusters);
>> +                                         &expanded_clusters, &nb_clusters,
>> +                                         &visited_l1_entries, l1_entries,
>> +                                         status_cb);
>>           if (ret < 0) {
>>               goto fail;
>>           }
>> diff --git a/block/qcow2.c b/block/qcow2.c
>> index 757f890..6e8c8ab 100644
>> --- a/block/qcow2.c
>> +++ b/block/qcow2.c
>> @@ -2147,7 +2147,8 @@ static int qcow2_load_vmstate(BlockDriverState *bs, uint8_t *buf,
>>    * Downgrades an image's version. To achieve this, any incompatible features
>>    * have to be removed.
>>    */
>> -static int qcow2_downgrade(BlockDriverState *bs, int target_version)
>> +static int qcow2_downgrade(BlockDriverState *bs, int target_version,
>> +                           BlockDriverAmendStatusCB *status_cb)
>>   {
>>       BDRVQcowState *s = bs->opaque;
>>       int current_version = s->qcow_version;
>> @@ -2196,7 +2197,7 @@ static int qcow2_downgrade(BlockDriverState *bs, int target_version)
>>       /* clearing autoclear features is trivial */
>>       s->autoclear_features = 0;
>>   
>> -    ret = qcow2_expand_zero_clusters(bs);
>> +    ret = qcow2_expand_zero_clusters(bs, status_cb);
>>       if (ret < 0) {
>>           return ret;
>>       }
>> @@ -2224,8 +2225,6 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
>>       int ret;
>>       QemuOptDesc *desc = opts->list->desc;
>>   
>> -    (void)status_cb;
>> -
>>       while (desc && desc->name) {
>>           if (!qemu_opt_find(opts, desc->name)) {
>>               /* only change explicitly defined options */
>> @@ -2291,7 +2290,7 @@ static int qcow2_amend_options(BlockDriverState *bs, QemuOpts *opts,
>>                   return ret;
>>               }
>>           } else {
>> -            ret = qcow2_downgrade(bs, new_version);
>> +            ret = qcow2_downgrade(bs, new_version, status_cb);
>>               if (ret < 0) {
>>                   return ret;
>>               }
>> diff --git a/block/qcow2.h b/block/qcow2.h
>> index b49424b..1c4f9bf 100644
>> --- a/block/qcow2.h
>> +++ b/block/qcow2.h
>> @@ -522,7 +522,8 @@ int qcow2_discard_clusters(BlockDriverState *bs, uint64_t offset,
>>       int nb_sectors, enum qcow2_discard_type type);
>>   int qcow2_zero_clusters(BlockDriverState *bs, uint64_t offset, int nb_sectors);
>>   
>> -int qcow2_expand_zero_clusters(BlockDriverState *bs);
>> +int qcow2_expand_zero_clusters(BlockDriverState *bs,
>> +                               BlockDriverAmendStatusCB *status_cb);
>>   
>>   /* qcow2-snapshot.c functions */
>>   int qcow2_snapshot_create(BlockDriverState *bs, QEMUSnapshotInfo *sn_info);
>> -- 
>> 2.0.3
>>
>>
> Reviewed-by: Benoit Canet <benoit@irqsave.net>