Re: [PATCH v2 01/15] scsi: Add struct for args to execution functions

[Bart Van Assche <bvanassche@acm.org>]

On 12/9/22 10:37, Mike Christie wrote:
> On 12/9/22 11:15 AM, Mike Christie wrote:
>> On 12/9/22 4:40 AM, John Garry wrote:
>>>>         * head injection*required*  here otherwise quiesce won't work
>>>> @@ -249,13 +238,14 @@ int __scsi_execute(struct scsi_device *sdev, const unsigned char *cmd,
>>>>        if (unlikely(scmd->resid_len > 0 && scmd->resid_len <= bufflen))
>>>>            memset(buffer + bufflen - scmd->resid_len, 0, scmd->resid_len);
>>>>    -    if (resid)
>>>> -        *resid = scmd->resid_len;
>>>> -    if (sense && scmd->sense_len)
>>>> -        memcpy(sense, scmd->sense_buffer, SCSI_SENSE_BUFFERSIZE);
>>>> -    if (sshdr)
>>>> -        scsi_normalize_sense(scmd->sense_buffer, scmd->sense_len,
>>>> -                     sshdr);
>>>> +    if (args.resid)
>>>> +        *args.resid = scmd->resid_len;
>>>> +    if (args.sense && scmd->sense_len)
>>>
>>> I am not sure that you require the sense_len check as you effectively have that same check in scsi_execute_args(), which is the only caller which would have args.sense set. But I suppose __scsi_execute() is still a public API (so should still check); but, by that same token, we have no sanity check for args.sense_len value here then. Is it possible to make __scsi_execute() non-public or move/add the check for proper sense_len here? I'm being extra cautious about this, I suppose.
>> Do people want the BUILD_BUG_ON we have now or a WARN/BUG?
>>
>> If we move to a single check in __scsi_execute or some non-macro wrapper
>> around it then we have to do a WARN/BUG. We do the macro approach now
>> so we can do the BUILD_BUG_ON.
> 
> Maybe we have to switch to a WARN/BUG.
> 
> It looks like some compilers don't like:
> 
> const struct scsi_exec_args exec_args = {
> 	.sshdr = &sshdr,
> };
> 
> scsi_execute_args(.... exec_args);
> 
> and will hit the:
> 
> #define scsi_execute_args(sdev, cmd, opf, buffer, bufflen, timeout,     \
>                            retries, args)                                \
> ({                                                                      \
>          BUILD_BUG_ON(args.sense &&                                      \
>                       args.sense_len != SCSI_SENSE_BUFFERSIZE);          \
> 
> because the args's sense and sense_len are not cleared yet.

My understanding is that the __scsi_execute() macro was introduced to 
prevent that every single scsi_execute() caller would have to be 
modified. I'm fine with removing the BUILD_BUG_ON(sense_len != 
SCSI_SENSE_BUFFER_SIZE) check and replacing it with a WARN_ON_ONCE() 
statement, e.g. inside __scsi_execute().

Thanks,

Bart.