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Re: Safe File Update (atomic)

On Sun, Jan 2, 2011 at 1:52 PM, Henrique de Moraes Holschuh
<hmh@debian.org> wrote:
> Olaf, O_ATOMIC is "difficult" in the kernel sense and in the long run.  It
> is an API that is too hard to implement in a sane way, with too many
> boundary conditions.
> OTOH, you don't need O_ATOMIC.  You need a way for easy application access
> to a saner/simpler way to deal with files that require atomic replacement.
> Time to switch to a plan B that can achieve it.  Do not lose track of your
> final goal, and stop wasting time with O_ATOMIC (and aggravating fs
> developers, which can only hurt your goal in the end).

Maybe I wasn't clear, in that case I'm sorry. To me, O_ATOMIC is
mostly about the userspace API. The implementation isn't (that)
important, so you're right.

> Maybe there are ways to actually let the kernel detect usage patterns and do
> the right thing, but nobody found any that is complete (and the incomplete
> ones are implemented in ext3 and ext4 AFAIK).
> If an userspace library is built to do all the dances required using only
> POSIX APIs (you can use extensions where they are available to enhance
> performance) you will have an EXACT list of boundary conditions and choke
> points.

A userspace lib is fine with me. In fact, I've been asking for it
multiple times. Result: no response.


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