linux-kernel - Re: [PATCH 0/5]scsi:scsi_debug: Add error injection for single device

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Date:   Thu, 23 Mar 2023 21:13:21 +0800
From:   "haowenchao (C)" <haowenchao2@...wei.com>
To:     John Garry <john.g.garry@...cle.com>,
        "James E . J . Bottomley" <jejb@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Douglas Gilbert <dgilbert@...erlog.com>,
        <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <linfeilong@...wei.com>, <louhongxiang@...wei.com>
Subject: Re: [PATCH 0/5]scsi:scsi_debug: Add error injection for single device

On 2023/3/23 20:40, John Garry wrote:
> On 23/03/2023 11:55, Wenchao Hao wrote:
>> The original error injection mechanism was based on scsi_host which
>> could not inject fault for a single SCSI device.
>>
>> This patchset provides the ability to inject errors for a single
>> SCSI device. Now we supports inject timeout errors, queuecommand
>> errors, and hostbyte, driverbyte, statusbyte, and sense data for
>> specific SCSI Command.
> 
> There is already a basic mechanism to generate errors - like timeouts - on "nth" command. Can you say why you want this new interface? What special scenarios are you trying to test/validate (which could not be achieved based on the current mechanism)?
>

I am testing a new error handle policy which is based on single scsi_device
without set host to RECOVERY. So I need a method to generate errors for
single SCSI devices.

While we can not generate errors for single device with current mechanism
because it is designed for host-wide error generation.
  
> With this series we would have 2x methods to inject errors, which is less than ideal, and they seem to possibly conflict as well, e.g. I set timeout for nth command via current interface and then use the new interface to set timeout for some other cadence. What behavior to expect ...?

I did not take this issue in consideration. I now assume the users would
not use these 2 methods at same time.

What's more, I don not know where to write the usage of this newly added
interface, maybe we can explain these in doc?

> 
> I'm not saying that I am a huge fan of the current inject mechanism, but at the very least you need to provide more justification for this series.
>>>
>> The first patch add an sysfs interface to add and inquiry single
>> device's error injection info; the second patch defined how to remove
>> an injection which has been added. The following 3 patches use the
>> injection info and generate the related error type.
>>
>> Wenchao Hao (5):
>>    scsi:scsi_debug: Add sysfs interface to manage scsi devices' error
>>      injection
>>    scsi:scsi_debug: Define grammar to remove added error injection
>>    scsi:scsi_debug: timeout command if the error is injected
>>    scsi:scsi_debug: Return failed value if the error is injected
>>    scsi:scsi_debug: set command's result and sense data if the error is
>>      injected
>>
>>   drivers/scsi/scsi_debug.c | 296 ++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 296 insertions(+)
>>
> 
>