linux-kernel - Response Summary Re: [rfc] Ignore Fsync Calls in Laptop

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Date:	Sun, 22 May 2011 11:01:57 +0200
From:	Dennis Jansen <Dennis.Jansen@....de>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, tytso@....edu
Subject: Response Summary Re: [rfc] Ignore Fsync Calls in Laptop_Mode

So just to summarize - correct me if I'm wrong:

There is general opposition to the idea of disabling fsync:
- whether automatically while in laptop mode or by user's choice, e.g.
via a special setting
- no matter what the fsync call would return - whether any error code or success
-> at all and in any form or context
in kernel space.

The reason seems to be mainly:
 - data security (esp. destruction of existing data in case of
ordering problems)
 - application compatibility (e.g. mailserver able to work according
to standards)
 - misuse potential (users not knowing what they're doing and/or how)
 - "Changing a generic, widely used kernel option"

There is a general distinction made between using laptop mode ("soft"
increased data loss risk) and disabling fsync (not providing a
guaranteed write when specificly asked for it).

There is no agreement:
- whether ordering guarantees would be an issue (in a "properly
implemented filesystem").

There was no response to:
- whether something like featherstick
(http://lwn.net/Articles/354861/) would make sense (in kernel space)
in this context.
- flame war suggestions ;)

The proposed solution is:
- to implement this in user space.

Thanks for everyone for their feedback!
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