linux-kernel - Re: [PATCH v2 15/16] block: sed-opal: don't repeat opal

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Date:   Sun, 20 Jan 2019 21:23:21 +0100 (CET)
From:   David Kozub <zub@...ux.fjfi.cvut.cz>
To:     Scott Bauer <sbauer@...donthack.me>
cc:     linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        hch@...radead.org, jonathan.derrick@...el.com
Subject: Re: [PATCH v2 15/16] block: sed-opal: don't repeat opal_discovery0
 in each steps array

On Sat, 19 Jan 2019, Scott Bauer wrote:

> On Thu, Jan 17, 2019 at 09:31:55PM +0000, David Kozub wrote:
>
>> -	for (state = 0; !error && state < n_steps; state++) {
>> -		step = &steps[state];
>> -
>> -		error = step->fn(dev, step->data);
>> -		if (error) {
>> -			pr_debug("Step %zu (%pS) failed with error %d: %s\n",
>> -				 state, step->fn, error,
>> -				 opal_error_to_human(error));
>> -
>> -			/* For each OPAL command we do a discovery0 then we
>> -			 * start some sort of session.
>> -			 * If we haven't passed state 1 then there was an error
>> -			 * on discovery0 or during the attempt to start a
>> -			 * session. Therefore we shouldn't attempt to terminate
>> -			 * a session, as one has not yet been created.
>> -			 */
>> -			if (state > 1) {
>> -				end_opal_session_error(dev);
>> -				return error;
>> -			}
>
>
>
>
>> +	/* first do a discovery0 */
>> +	error = opal_discovery0_step(dev);
>>
>> -		}
>> -	}
>> +	for (state = 0; !error && state < n_steps; state++)
>> +		error = execute_step(dev, &steps[state], state);
>> +
>> +	/* For each OPAL command the first step in steps starts some sort
>> +	 * of session. If an error occurred in the initial discovery0 or if
>> +	 * an error stopped the loop in state 0 then there was an error
>> +	 * before or during the attempt to start a session. Therefore we
>> +	 * shouldn't attempt to terminate a session, as one has not yet
>> +	 * been created.
>> +	 */
>> +	if (error && state > 0)
>> +		end_opal_session_error(dev);
>
>
> This is subtly wrong. There was some state that was encoded by having the
> loop the way we did.
>
> the tl;dr is the check needs to be if (error && state > 1) still.
>
> The why is that in the previous implementation we wanted to end_opal_session_error
> only if a successful discovery0 AND a successful start_*_session. In the previous loop,
> discovery0 would complete, we'd do state++, then we'd go and attempt to start our
> session. If we failed on that session starting we'd still be in state 1, and wouldn't
> attempt to close the session.
>
> In the current form, discovery0 is gone, so start session is on state 0. If we fail
> on the start session, we set error = true, state gets ++'d, then we look at !error
> and we don't loop again.
>
> We go down to the check and attempt to end a session that was never started.

Ouch! You're right. I'll fix this for v3 by comparing against 1.

There is one more issue that was bugging me. If next() fails at the 
discovery0 step, or at steps[0], in both cases the error message will say 
step 0 failed. But as it's just a pr_debug message, the function address 
is included and I don't see a short and nice solution (should I report the 
steps as starting from 1? but that might be confusing; or a different 
string? sounds like not worth it), I kept it that way.

But if someone thinks this is worth improving, please let me know.