[PATCH] kernel: force atomic renames in ubifs

[Rafał Miłecki]

Hi Richard,

On 1.03.2022 20:37, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
>> Von: "Rafał Miłecki" <zajec5 at gmail.com>
>> An: "OpenWrt Development List" <openwrt-devel at lists.openwrt.org>
>> CC: "Koen Vandeputte" <koen.vandeputte at ncentric.com>, "richard" <richard at nod.at>, "Rafał Miłecki" <rafal at milecki.pl>
>> Gesendet: Dienstag, 1. März 2022 20:13:29
>> Betreff: [PATCH] kernel: force atomic renames in ubifs
> 
>> From: Rafał Miłecki <rafal at milecki.pl>
>>
>> This deals with user-spaces apps that don't handle all syncing
>> correctly. It prevents user ending up with an empty file.
>>
>> Signed-off-by: Rafał Miłecki <rafal at milecki.pl>
>> ---
>> .../510-ubifs-force-atomic-renames.patch      | 46 +++++++++++++++++++
>> .../510-ubifs-force-atomic-renames.patch      | 46 +++++++++++++++++++
>> 2 files changed, 92 insertions(+)
>> create mode 100644
>> target/linux/generic/pending-5.10/510-ubifs-force-atomic-renames.patch
>> create mode 100644
>> target/linux/generic/pending-5.4/510-ubifs-force-atomic-renames.patch
>>
>> diff --git
>> a/target/linux/generic/pending-5.10/510-ubifs-force-atomic-renames.patch
>> b/target/linux/generic/pending-5.10/510-ubifs-force-atomic-renames.patch
>> new file mode 100644
>> index 0000000000..80f5f1b910
>> --- /dev/null
>> +++ b/target/linux/generic/pending-5.10/510-ubifs-force-atomic-renames.patch
>> @@ -0,0 +1,46 @@
>> +From: Richard Weinberger <richard at nod.at>
>> +Date: Mon, 28 Feb 2022 16:07:41 +0100
>> +Subject: [PATCH] ubifs: force atomic renames
>> +MIME-Version: 1.0
>> +Content-Type: text/plain; charset=UTF-8
>> +Content-Transfer-Encoding: 8bit
>> +
>> +Before actual rename make sure that the old inode data has been flash
>> +written. This is similar to what other filesystems do and workarounds
>> +bugs in some user-space apps.
>> +
>> +With this change updating file using tmpfile & rename() will never
>> +result in losing all content e.g. on power cut.
> 
> Please slow down a bit. :-)
> The commit message is not written by me and also not entirely correct.
> 
> The patch is not about making rename atomic. rename is already atomic
> on UBIFS.
> It is about syncing in flight pages when a file is overwritten by rename.
> 
> While I plan to upstream this change it still needs more testing.
> I'm also not sure about the overhead it causes. Flushing the write buffers
> can cause more garbage collection and may trigger write amplification.

I didn't end up pushing this change to OpenWrt since your e-mail. I use
it however in my project in production in thousands of devices. I'd very
much like to see a proper change upstream.

Could you take a look at it, please?