Re: [Qemu-devel] [Qemu-block] [PATCH v4 10/10] block/blklogwrites: Use the block device logical sector size when logging writes

[Alberto Garcia]

On Mon 18 Jun 2018 05:53:50 PM CEST, Ari Sundholm wrote:
> On 06/18/2018 06:36 PM, Alberto Garcia wrote:
>> On Fri 08 Jun 2018 02:32:28 PM CEST, Ari Sundholm wrote:
>>> The guest OS may perform writes which are aligned to the logical
>>> sector size instead of the physical one, so logging at this granularity
>>> records the writes performed on the block device most faithfully.
>>>
>>> Signed-off-by: Ari Sundholm <address@hidden>
>>> ---
>>>   block/blklogwrites.c | 47 ++++++++++++++++++++++++++++++++---------------
>>>   1 file changed, 32 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/block/blklogwrites.c b/block/blklogwrites.c
>>> index 216367f..decf5e5 100644
>>> --- a/block/blklogwrites.c
>>> +++ b/block/blklogwrites.c
>>> @@ -47,6 +47,8 @@ struct log_write_entry {
>>>   
>>>   typedef struct {
>>>       BdrvChild *log_file;
>>> +    uint32_t sectorsize;
>>> +    uint32_t sectorbits;
>>>       uint64_t cur_log_sector;
>>>       uint64_t nr_entries;
>>>   } BDRVBlkLogWritesState;
>>> @@ -67,6 +69,8 @@ static int blk_log_writes_open(BlockDriverState *bs, 
>>> QDict *options, int flags,
>>>           goto fail;
>>>       }
>>>   
>>> +    s->sectorsize = BDRV_SECTOR_SIZE; /* May be updated later */
>>> +    s->sectorbits = BDRV_SECTOR_BITS;
>>>       s->cur_log_sector = 1;
>>>       s->nr_entries = 0;
>> 
>> I haven't looked closely into this series so sorry if there's something
>> that I'm overlooking, but this caught my attention: why do you have a
>> patch that improves a driver that you introduced earlier in this same
>> series?
>> 
>
> I guess there is no other real reason than that it reflects the
> development history of the driver more closely: the code by the
> original author did not contain proper support for non-512 sector
> sizes. I then added the parts needed for this.

Ah I see, so the driver was originally written by someone else and you
improved it.

As I said I haven't looked closely into the code (I hope I'll have time
to do it after I'm done with my blockdev-reopen work) so perhaps there's
good reason for this in this case, but in general I think that reviews
are simpler if one doesn't need to review code that is going to be
modified in the following patch.

> The series could be restructured in the following manner if that makes
> it more reviewable (prerequisites first, then the entire driver):

I just want to clarify that the code looks reviewable as it is now, it's
not like this is a blocker (for reviews at least) :)

> - Patch 1: as before
> - Patches 2-7: introduction of the mechanism to pass block
> configurations to drivers + changes to block device implementations to
> make them pass on this information (current patches 3-8)
> - Patch 8: Introduction of the blklogwrites driver (current patches 2,
> 9 and 10, squashed)
>
> Does that sound like a good idea?

It does, yes.

Thanks!

Berto