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!