linux-kernel - Re: [PATCH] zram: check compressor name before setting it

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Date:	Fri, 22 May 2015 15:34:36 +0200
From:	Marcin Jabrzyk <m.jabrzyk@...sung.com>
To:	Minchan Kim <minchan@...nel.org>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc:	ngupta@...are.org, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kyungmin.park@...sung.com
Subject: Re: [PATCH] zram: check compressor name before setting it


Hello Minchan,

On 22/05/15 15:14, Minchan Kim wrote:
> Hello Sergey,
>
> On Fri, May 22, 2015 at 09:44:11PM +0900, Sergey Senozhatsky wrote:
>> On (05/22/15 11:12), Marcin Jabrzyk wrote:
>>>>
>>>> no.
>>>>
>>>> zram already complains about failed comp backend creation.
>>>> it's in dmesg (or syslog, etc.):
>>>>
>>>> 	"zram: Cannot initialise %s compressing backend"
>>>>
>>> OK, now I see that. Sorry for the noise.
>>>
>>>> second, there is not much value in exposing zcomp internals,
>>>> especially when the result is just another line in dmesg output.
>>>
>>>  From the other hand, the only valid values that can be written are
>>> in 'comp_algorithm'.
>>> So when writing other one, returning -EINVAL seems to be reasonable.
>>> The user would get immediately information that he can't do that,
>>> now the information can be very deferred in time.
>>
>> it's not.
>> the error message appears in syslog right before we return -EINVAL
>> back to user.
>
> Although Marcin's description is rather misleading, I like the patch.
> Every admin doesn't watch dmesg output. Even people could change loglevel
> simply so KERN_INFO would be void in that case.
Sorry for being confusing, at the first time I've overlooked that error 
message in syslog.
I didn't thought about looking for handling exactly this error in 
completely different place.

>
> Instant error propagation is more strighforward for user point of view
> rather than delaying with depending on another event.

Yes this was my exact motivation.
Instant value can be detected in scripts etc. Easier to debug in
automated environment.

>
> Thanks.
>
>>
>> 	-ss
>>
>>> I'm not for exposing more internals, but getting -EINVAL would be nice I
>

If this would be ok, I can prepare v2 with better description and with
less exposing zcomp internals.

Best regards,
Marcin Jabrzyk

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