EXT4 "meets" the POSIX specifications for filesystems. The specification does not make any requirements for data to be written out in any order - and for very good reason. If the application developer -requires- data to be written out in order, they should serialise their operations through use of fsync(). If they do -not- require it, then the operating system should be free to optimise away the physical IO operations.
As a clueful(!) application developer, -I- appreciate being given the opportunity to provide this kind of feedback to the operating system. I don't want one or the other. I'd like to be able to use both where and when I choose.
Application developers - stop being stupid. Fix your applications. Read and understand the specification and what it provides -everyone- rather than just you.
3 comments:
What about shell scripts? No shell (I checked ksh93, bash and zsh) fsyncs before close, so `echo foo >> bar.tmp && mv bar.tmp bar` is vulnerable. Calling sync(1) is no good, since that just calls sync(2) which can return before it completes.
Then the shells need to be fixed? :)
Which leads to the "everyone calling fsync all the time" which leads to people suggesting "yes-I-really-mean-it" flags for fsync.
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