Why is it not ok to have the writes come out intermingled, if that's what the
user has asked for? (Implicitly, by not synchronizing the writes.)
> Irix actually takes the viewpoint that it only needs to make a best effort
> at synchronizing between direct I/O and other modes of I/O. Multiple
> direct writers are allowed into a file at once, and direct writers and
> buffered readers are also allowed to operate in parallel. At this point
> coherency is really up to the applications. I am not presenting this as
> a recommended model for linux, just reporting what it does.
I'm having a little trouble with this. Suppose an application does direct
IO on a file but, unbeknownst to it, some other program has done buffered
IO on the file, so that there are still dirty blocks in the page cache,
waiting to land by surprise on top of unbuffered data. A third program
may come along to do buffered IO on the file, and find stale blocks in
cache. Am I missing something here?
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