On Mon, Sep 12, 2016 at 06:05:07PM +1000, Nicholas Piggin wrote:

It's not fundamentally broken, it just doesn't fit well existing
filesystems.

Or the existing file system architecture for that matter.  Which makes
it a fundamentally broken model.

Dave's post of requirements is also wrong. A filesystem does not have
to guarantee all that, it only has to guarantee that is the case for
a given block after it has a mapping and page fault returns, other
operations can be supported by invalidating mappings, etc.

Which doesn't really matter if your use case is manipulating
fully mapped files.

But back to the point: if you want to use a full blown Linux or Unix
filesystem you will always have to fsync (or variants of it like msync),
period.

If you want a volume manager on stereoids that hands out large chunks
of storage memory that can't ever be moved, truncated, shared, allocated
on demand, etc - implement it in your library on top of a device file.

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