Re: RFC: O_PONIES semantics (well O_REWRITE)

[Rik van Riel <riel@redhat.com>]

Trond Myklebust wrote:

> How is this any different than just having your application use
> mkostemp() to create a temporary dot file, then renaming it when done
> writing?

That is exactly what it is.  There are reasons for implementing
it at a lower level in the system, though.

Implementing it in glibc:
- means applications get it right (today, many don't)
- allows for a performance optimization, moving the fsync
   into a specially spawned off temporary thread, so the
   main application doesn't stall

Implementing it in the kernel allows for some further
performance and power optimizations, most notably:
- the sync could be turned into an ordering requirement,
   meaning it can be postponed and even obsoleted by a
   future version of the file
- the ability to postpone the write allows for better
   power saving

-- 
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