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Re: [Qemu-block] [PATCH 16/17] block: Make bdrv_is_allocated() byte-base
From: |
John Snow |
Subject: |
Re: [Qemu-block] [PATCH 16/17] block: Make bdrv_is_allocated() byte-based |
Date: |
Wed, 19 Apr 2017 15:37:00 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.0 |
On 04/19/2017 01:54 PM, Eric Blake wrote:
> On 04/18/2017 05:15 PM, John Snow wrote:
>
>>> @@ -279,9 +280,9 @@ static int mig_save_device_bulk(QEMUFile *f,
>>> BlkMigDevState *bmds)
>>> /* Skip unallocated sectors; intentionally treats failure as
>>> * an allocated sector */
>>> while (cur_sector < total_sectors &&
>>> - !bdrv_is_allocated(blk_bs(bb), cur_sector,
>>> - MAX_IS_ALLOCATED_SEARCH, &nr_sectors)) {
>>> - cur_sector += nr_sectors;
>>> + !bdrv_is_allocated(blk_bs(bb), cur_sector *
>>> BDRV_SECTOR_SIZE,
>>> + MAX_IS_ALLOCATED_SEARCH, &count)) {
>>> + cur_sector += DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
>>
>> Hm, what's the story here, why are we rounding this up? If, in theory,
>> we have a partially allocated cluster won't we advance past that?
>
> This is rounding to sectors, not clusters (that is, the code is supposed
> to advance cur_sector identically pre- and post-patch). As to whether
> the overall algorithm makes sense, or could use some tweaking by
> converting migration/block.c to do everything by bytes instead of by
> sectors, I haven't yet given that any serious time.
>
Err, right... temporary brain schism. DIV_ROUND_UP not ALIGN_UP, my mistake.
>
- [Qemu-block] [PATCH 11/17] mirror: Switch mirror_iteration() to byte-based, (continued)
- [Qemu-block] [PATCH 11/17] mirror: Switch mirror_iteration() to byte-based, Eric Blake, 2017/04/11
- [Qemu-block] [PATCH 12/17] backup: Switch BackupBlockJob to byte-based, Eric Blake, 2017/04/11
- [Qemu-block] [PATCH 13/17] backup: Switch block_backup.h to byte-based, Eric Blake, 2017/04/11
- [Qemu-block] [PATCH 14/17] backup: Switch backup_do_cow() to byte-based, Eric Blake, 2017/04/11
- [Qemu-block] [PATCH 15/17] backup: Switch backup_run() to byte-based, Eric Blake, 2017/04/11
- [Qemu-block] [PATCH 16/17] block: Make bdrv_is_allocated() byte-based, Eric Blake, 2017/04/11
- Re: [Qemu-block] [PATCH 16/17] block: Make bdrv_is_allocated() byte-based, John Snow, 2017/04/19
[Qemu-block] [PATCH 17/17] block: Make bdrv_is_allocated_above() byte-based, Eric Blake, 2017/04/11
Re: [Qemu-block] [PATCH 00/17] make bdrv_is_allocated[_above] byte-based, John Snow, 2017/04/17