Re: [PATCH v2 3/8] parallels: Replace bdrv_co_pwrite_sync by bdrv_co_flush for BAT flushing

[Denis V. Lunev]

Use generic infrastructure for BAT writing in parallels_co_check()

On 11.08.2022 17:00, Alexander Ivanov wrote:
> It's too costly to write all the BAT to the disk. Let the flush function
> write only dirty blocks.
> Use parallels_set_bat_entry for setting a BAT entry and marking a relevant
> block as dirty.
> Move bdrv_co_flush call outside the locked area.
This is not correct too:
- with a lot of cases inside parallels_co_check, which will be split to
  smaller functions, we would like to avoid writing BAT once each
  stage is complete

Thus the comment should look like the following:
"BAT is written in the context of conventional operations over
the image inside bdrv_co_flush() when it calls
parallels_co_flush_to_os() callback. Thus we should not
modify BAT array directly, but call parallels_set_bat_entry()
helper and bdrv_co_flush() further on. After that there is no
need to manually write BAT and track its modification.

This makes code more generic and allows to split
parallels_set_bat_entry() for independent pieces."

> v2: Patch order was changed so the replacement is done in parallels_co_check.
>      Now we use a helper to set BAT entry and mark the block dirty.
Same note about changelog as n other patches.

Side note. I like Linux kernel a lot and there is a good
guide in. Please look how commit message
https://www.kernel.org/doc/html/latest/process/submitting-patches.html

May be you could spend some more time on commit
message.

With a better message:
Reviewed-by: Denis V. Lunev <den@openvz.org>

> Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
> ---
>   block/parallels.c | 19 +++++++------------
>   1 file changed, 7 insertions(+), 12 deletions(-)
>
> diff --git a/block/parallels.c b/block/parallels.c
> index 7f68f3cbc9..6879ea4597 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -428,7 +428,6 @@ static int coroutine_fn parallels_co_check(BlockDriverState 
> *bs,
>       int64_t size, prev_off, high_off;
>       int ret;
>       uint32_t i;
> -    bool flush_bat = false;
>   
>       size = bdrv_getlength(bs->file->bs);
>       if (size < 0) {
> @@ -467,9 +466,8 @@ static int coroutine_fn parallels_co_check(BlockDriverState 
> *bs,
>               res->corruptions++;
>               if (fix & BDRV_FIX_ERRORS) {
>                   prev_off = 0;
> -                s->bat_bitmap[i] = 0;
> +                parallels_set_bat_entry(s, i, 0);
>                   res->corruptions_fixed++;
> -                flush_bat = true;
>                   continue;
>               }
>           }
> @@ -485,15 +483,6 @@ static int coroutine_fn 
> parallels_co_check(BlockDriverState *bs,
>           prev_off = off;
>       }
>   
> -    ret = 0;
> -    if (flush_bat) {
> -        ret = bdrv_co_pwrite_sync(bs->file, 0, s->header_size, s->header, 0);
> -        if (ret < 0) {
> -            res->check_errors++;
> -            goto out;
> -        }
> -    }
> -
>       res->image_end_offset = high_off + s->cluster_size;
>       if (size > res->image_end_offset) {
>           int64_t count;
> @@ -522,6 +511,12 @@ static int coroutine_fn 
> parallels_co_check(BlockDriverState *bs,
>   
>   out:
>       qemu_co_mutex_unlock(&s->lock);
> +
> +    ret = bdrv_co_flush(bs);
> +    if (ret < 0) {
> +        res->check_errors++;
> +    }
> +
>       return ret;
>   }
>