Re: [PATCH V2] scsi: add a new flag to set whether SCSI disks support WRITE_SAME_16 by default

[AlexChen <alex.chen@huawei.com>]

Hi Martin,

Are there any other opinions about this patch? If so, I can make
corresponding modifications.

Thanks
Alex
On 2020/2/7 16:51, AlexChen wrote:
> Hi Martin,
> 
> Thanks for your reply.
> 
>>> When the SCSI device is initialized, check whether it supports
>>> WRITE_SAME_16 or WRITE_SAME_10 in the sd_read_write_same(). If the
>>> back-end storage device does not support queries, it will not set
>>> sdkp->ws16 as 1.
>>
>> Your proposed code change is fine and to the point. However, I'd like to
>> understand why you are adding a workaround to the kernel instead of
>> fixing the affected device?
>>
>> Implementing support for either WRITE SAME(10) or REPORT SUPPORTED
>> OPERATION CODES is easy. And the latter in particular is beneficial for
>> discovering several other SCSI protocol features. It's a good command to
>> support in general.
>>
> 
>>From a maintenance perspective, I think the old storage device which does
> not support WRITE SAME query interface can be easily supported by adding
> a workaround to the kernel, instead of waiting for the storage device to
> implement the query interface.
> 
>> Also, we generally don't add features to the kernel without any
>> users. So if you add a blacklist flag, I would expect to see a set of
>> device strings to be added to scsi_devinfo.c.
> 
> Through my test, I found that HUAWEI's storage devices do not provide
> queries for WRITE_SAME_16 support.
> If the lists of such devices is written into the kernel code, will it
> be incomplete and difficult to maintain? On the other hand, It would be
> more flexible if we provided the module parameter 'dev_flags' to set.
> 
> Thanks
> Alex
>