linux-kernel - Re: [PATCH] scsi: Let scsi_execute_cmd() mark args->sshdr as invalid

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Date:   Fri, 19 May 2023 18:12:01 +0100
From:   John Garry <john.g.garry@...cle.com>
To:     Bart Van Assche <bvanassche@....org>,
        Juergen Gross <jgross@...e.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc:     linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>, stable@...r.kernel.org
Subject: Re: [PATCH] scsi: Let scsi_execute_cmd() mark args->sshdr as invalid

On 19/05/2023 17:54, Bart Van Assche wrote:
> On 5/19/23 09:06, John Garry wrote:
>> Sure, what I describe is ideal, 

* not ideal

To be clear, I mean something like:

struct scsi_exec_args {
	unsigned char **sense;
}

scsi_execute_cmd()
{
	...
	*args->sense = kmemdup(scsi_cmd->sense_buffer);
	...
}

some_func()
{
	unsigned char *sense = NULL;
	struct  scsi_exec_args = {
		.sense = &sense,
	};

	ret = scsi_execute_cmd();
	if (ret < 0)
		return ret;
	kfree(sense);
}

But not perfect as we need a separate small buffer for sensehdr and we 
need to always kfree those buffers.

If only we could pass the actual scsi_cmnd sense buffer to the caller...

>but I still just dislike passing both 
>> sensebuf and hdr into scsi_execute_cmd(). The semantics of how 
>> scsi_execute_cmd() treats them is vague.
> 
> Is this something that can be addressed by improving the 
> scsi_execute_cmd() documentation?

Hmmm, I'm not sure documentation helps too much avoiding all programming 
errors and better make the code foolproof.

Anyway, if we fix up the callers of scsi_execute_cmd() to properly check 
for errors then if is not such a big deal.

Thanks,
John