Re: [Qemu-block] [Qemu-devel] [PATCH 1/3] block/backup: deal with zero detection

[John Snow]

On 7/31/19 6:01 AM, Vladimir Sementsov-Ogievskiy wrote:
> 30.07.2019 21:40, John Snow wrote:
>>
>>
>> On 7/30/19 12:32 PM, Vladimir Sementsov-Ogievskiy wrote:
>>> We have detect_zeroes option, so at least for blockdev-backup user
>>> should define it if zero-detection is needed. For drive-backup leave
>>> detection enabled by default but do it through existing option instead
>>> of open-coding.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>> ---
>>>   block/backup.c | 15 ++++++---------
>>>   blockdev.c     |  8 ++++----
>>>   2 files changed, 10 insertions(+), 13 deletions(-)
>>>
>>> diff --git a/block/backup.c b/block/backup.c
>>> index 715e1d3be8..f4aaf08df3 100644
>>> --- a/block/backup.c
>>> +++ b/block/backup.c
>>> @@ -110,7 +110,10 @@ static int coroutine_fn 
>>> backup_cow_with_bounce_buffer(BackupBlockJob *job,
>>>       BlockBackend *blk = job->common.blk;
>>>       int nbytes;
>>>       int read_flags = is_write_notifier ? BDRV_REQ_NO_SERIALISING : 0;
>>> -    int write_flags = job->serialize_target_writes ? BDRV_REQ_SERIALISING 
>>> : 0;
>>> +    int write_flags =
>>> +            (job->serialize_target_writes ? BDRV_REQ_SERIALISING : 0) |
>>> +            (job->compress ? BDRV_REQ_WRITE_COMPRESSED : 0);
>>> +
>>>   
>>>       assert(QEMU_IS_ALIGNED(start, job->cluster_size));
>>>       hbitmap_reset(job->copy_bitmap, start, job->cluster_size);
>>> @@ -128,14 +131,8 @@ static int coroutine_fn 
>>> backup_cow_with_bounce_buffer(BackupBlockJob *job,
>>>           goto fail;
>>>       }
>>>   
>>> -    if (buffer_is_zero(*bounce_buffer, nbytes)) {
>>> -        ret = blk_co_pwrite_zeroes(job->target, start,
>>> -                                   nbytes, write_flags | 
>>> BDRV_REQ_MAY_UNMAP);
>>> -    } else {
>>> -        ret = blk_co_pwrite(job->target, start,
>>> -                            nbytes, *bounce_buffer, write_flags |
>>> -                            (job->compress ? BDRV_REQ_WRITE_COMPRESSED : 
>>> 0));
>>> -    }
>>> +    ret = blk_co_pwrite(job->target, start, nbytes, *bounce_buffer,
>>> +                        write_flags);
>>>       if (ret < 0) {
>>>           trace_backup_do_cow_write_fail(job, start, ret);
>>>           if (error_is_read) {
>>> diff --git a/blockdev.c b/blockdev.c
>>> index 4d141e9a1f..a94d754504 100644
>>> --- a/blockdev.c
>>> +++ b/blockdev.c
>>> @@ -3434,7 +3434,7 @@ static BlockJob *do_drive_backup(DriveBackup *backup, 
>>> JobTxn *txn,
>>>       BlockJob *job = NULL;
>>>       BdrvDirtyBitmap *bmap = NULL;
>>>       AioContext *aio_context;
>>> -    QDict *options = NULL;
>>> +    QDict *options;
>>>       Error *local_err = NULL;
>>>       int flags, job_flags = JOB_DEFAULT;
>>>       int64_t size;
>>> @@ -3529,10 +3529,10 @@ static BlockJob *do_drive_backup(DriveBackup 
>>> *backup, JobTxn *txn,
>>>           goto out;
>>>       }
>>>   
>>> +    options = qdict_new();
>>> +    qdict_put_str(options, "discard", "unmap");
>>> +    qdict_put_str(options, "detect-zeroes", "unmap");
>>>       if (backup->format) {
>>> -        if (!options) {
>>> -            options = qdict_new();
>>> -        }
>>>           qdict_put_str(options, "driver", backup->format);
>>>       }
>>>   
>>>
>>
>> I'm less sure of this one personally. Is it right to always try to set
>> unmap on the target?
>>
>> I like the idea of removing special cases and handling things more
>> centrally though, but I'll want Max (or Kevin) to take a peek.
>>
>> --js
>>
> 
> 
> If nobody minds I'd agree with you to drop zero detecting from both backups.
> 

I'm not sure it's WRONG either!