Re: [Qemu-block] [PATCH v5 14/38] block: Remove wr_highest_sector from BlockAcctStats

[Eric Blake]

On 09/18/2015 09:22 AM, Max Reitz wrote:
> BlockAcctStats contains statistics about the data transferred from and
> to the device; wr_highest_sector does not fit in with the rest.
> 
> Furthermore, those statistics are supposed to be specific for a certain
> device and not necessarily for a BDS (see the comment above
> bdrv_get_stats()); on the other hand, wr_highest_sector may be a rather
> important information to know for each BDS. When BlockAcctStats is
> finally removed from the BDS, we will want to keep wr_highest_sector in
> the BDS.
> 
> Finally, wr_highest_sector is renamed to wr_highest_offset and given the
> appropriate meaning. Externally, it is represented as an offset so there
> is no point in doing something different internally. Its definition is
> changed to match that in qapi/block-core.json which is "the offset after
> the greatest byte written to". Doing so should not cause any harm since
> if external programs tried to calculate the volume usage by
> (wr_highest_offset + 512) / volume_size, after this patch they will just
> assume the volume to be full slightly earlier than before.
> 
> Signed-off-by: Max Reitz <address@hidden>
> Reviewed-by: Eric Blake <address@hidden>
> Reviewed-by: Alberto Garcia <address@hidden>

Still holds, but...

> +++ b/qmp-commands.hx
> @@ -2481,8 +2481,8 @@ Each json-object contain the following:
>      - "wr_total_time_ns": total time spend on writes in nano-seconds 
> (json-int)
>      - "rd_total_time_ns": total time spend on reads in nano-seconds 
> (json-int)
>      - "flush_total_time_ns": total time spend on cache flushes in 
> nano-seconds (json-int)
> -    - "wr_highest_offset": Highest offset of a sector written since the
> -                           BlockDriverState has been opened (json-int)
> +    - "wr_highest_offset": The offset after the greatest byte written to the
> +                           BlockDriverState since it has been opened 
> (json-int)

...someday, I'd really like to have this stat show as non-zero even when
first opening the device (before writing to it). Right now, you have no
clue how full a backing device is prior to starting a block-commit; you
have to start writing to it to get a feel for its current usage.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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