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Date: Sun, 09 Feb 2014 00:13:11 +0100
From: Richard Weinberger <richard@nod.at>
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To: Willy Tarreau <w@1wt.eu>
Subject: Re: [PATCH 1/1] ubi: Introduce block devices for UBI volumes
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Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>,
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Am 09.02.2014 00:01, schrieb Willy Tarreau:
> On Sat, Feb 08, 2014 at 11:56:02PM +0100, Richard Weinberger wrote:
>> Am 08.02.2014 23:51, schrieb Willy Tarreau:
>>> On Sat, Feb 08, 2014 at 10:37:19PM +0100, Richard Weinberger wrote:
>>>>> +config MTD_UBI_BLOCK_WRITE_SUPPORT
>>>>> +       bool "Enable write support (DANGEROUS)"
>>>>> +       default n
>>>>> +       depends on MTD_UBI_BLOCK
>>>>> +       select MTD_UBI_BLOCK_CACHED
>>>>> +       help
>>>>> +          This is a *very* dangerous feature. Using a regular block-oriented
>>>>> +          filesystem might impact heavily on a flash device wear.
>>>>> +          Use with extreme caution.
>>>>> +
>>>>> +          If in doubt, say "N".
>>>>
>>>> I really vote for dropping write support at all.
>>>
>>> Why ? When you put a read-only filesystem there such as squashfs, the
>>> only writes you'll have will be updates, and write support will be the
>>> only way to update the filesystem. So removing write support seriously
>>> impacts the usefulness of the feature itself.
>>
>> So almost everyone has to enable MTD_UBI_BLOCK_WRITE_SUPPORT?
>> I thought there is another way to fill the volume with data...
> 
> I personally don't see the use of disabling write support on anything
> unless the code is broken. Better emit a warning upon first write to
> mention that there is limited or no wear leveling. But preventing all
> reasonable users from using a useful feature just to save a few ignorant
> from shooting themselves in the foot is non-sense in my opinion.

As Piergiorgio wrote, one can use ubiupdatevol to update his squashfs.
There is simply no use case for MTD_UBI_BLOCK_WRITE_SUPPORT.

> Why not disable write support to ubifs as well then, so that we're
> sure that the most demanding ones will never wear their NANDs ? And
> why not disable mtdblock so that nobody can mount them as ext2 ? If
> people can already do bad things more easily without this code,
> there is no reason to remove the feature.

I'd like to avoid another mtdblock.

Thanks,
//richard