linux-kernel - Re: [PATCH 3/6] UBI: Fastmap: Notify user in case of an ubi_update

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Date:	Mon, 08 Dec 2014 10:11:48 +0100
From:	Richard Weinberger <richard@....at>
To:	Tanya Brokhman <tlinder@...eaurora.org>, dedekind1@...il.com
CC:	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] UBI: Fastmap: Notify user in case of an ubi_update_fastmap()
 failure

Hi!

Am 08.12.2014 um 07:58 schrieb Tanya Brokhman:
> On 12/7/2014 4:22 PM, Richard Weinberger wrote:
>> Am 07.12.2014 um 14:59 schrieb Tanya Brokhman:
>>> Hi Richard,
>>>
>>> On 11/30/2014 1:35 PM, Richard Weinberger wrote:
>>>> If ubi_update_fastmap() fails notify the user.
>>>> This is not a hard error as ubi_update_fastmap() makes sure that upon failure
>>>> the current on-flash fastmap will no be used upon next UBI attach.
>>>>
>>>> Signed-off-by: Richard Weinberger <richard@....at>
>>>> ---
>>>>    drivers/mtd/ubi/wl.c | 6 +++++-
>>>>    1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
>>>> index 523d8a4..7821342 100644
>>>> --- a/drivers/mtd/ubi/wl.c
>>>> +++ b/drivers/mtd/ubi/wl.c
>>>> @@ -657,7 +657,11 @@ again:
>>>>         * refill the WL pool synchronous. */
>>>>        if (pool->used == pool->size || wl_pool->used == wl_pool->size) {
>>>>            spin_unlock(&ubi->wl_lock);
>>>> -        ubi_update_fastmap(ubi);
>>>> +        ret = ubi_update_fastmap(ubi);
>>>> +        if (ret) {
>>>> +            ubi_msg(ubi, "Unable to write a new fastmap: %i", ret);
>>>> +            return -ENOSPC;
>>>
>>> Why do you fail the whole function (ubi_wl_get_peb) if fastmap update failed? Its possible that the fm_pools were refilled correctly, and the actual fastmap_write failed, so there
>>> is nothing preventing the user to get peb allocated and continue working. You invalidate the fastmap, so if powercut occurs a full scan will be performed. So its possible to
>>> allocate from fm_pools (although fastmap is not valid on disc) and try writing fastmap again when the pools filled up.
>>> I'm for the ubi_msg but against "return -ENOSPC;"
>>
>> Maybe the case you've described is powercut safe, but there can be other unsafe cases.
>> Let's stay on the safe side and be paranoid, it does not hurt.
>> If fastmap has proven stable we can start with tricky optimizations.
> 
> I'm sorry that I'm being petty here but the commit msg states that you "notify the user in case of update fastamap failure". It says nothing about you failing ubi_wl_get_peb as
> well. And this is a major change. At least divide this into 2 patches (so I can disagree to the function failing and agree to the msg to user :) )

With user I meant users of that function.

Thanks,
//richard
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