linux-kernel - Re: [PATCH 1/1] Blackfin OTP Char Driver: add writing support of OTP

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Date:	Mon, 13 Oct 2008 12:35:27 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Mike Frysinger <vapier.adi@...il.com>
CC:	Bryan Wu <cooloney@...nel.org>, sam@...nborg.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] Blackfin OTP Char Driver: add writing support of
 OTP

On 10/13/2008 12:07 PM, Mike Frysinger wrote:
> the pos gets updated every time a half-page gets processed.  so if you
> call write() and tell it to write 128 bytes, but you get an error half
> way through, the pos points right at the place where the error
> occurred.  i dont get what you're asking.

Ah, OK, that's because I don't know exactly what should happen if a write fails.
I though userspace expects the state of the fd to not be touched.

>> But is this OK to you:
>> PROCESS 1                       PROCESS 2
>> lock
>>  set allow_writes
>> write
>>   check allow_writes
>>   be interrupted
>>                                whatever
>>                                unlock
>>                                    unset allow_writes
>>                                sleep
>>   mutex lock
>>   the processing...
> 
> i dont see a problem here.  there is no loss of data, hardware
> failure, software crashes, etc...  in other words, there is no
> misbehavior.

I see no purpose of allow_writes then. Why is it there? I don't need to call
memlock if anybody else did and I raced with him. Also when somebody else
unlocks after finishing of writes I can start failing in the middle of my writes
-- this doesn't have anything to do with locking, but with the design, the one
global variable.
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