> > All file systems provide writes by default which are
> > atomic with respect to readers of the file.
>
> Surely, only in the absence of a crash - otherwise,
> POSIX would require implementation of transactional
> write semantics in all file systems.  Or is that what
> you meant by the last sentence in your post?

Well, that's part of what I meant, but the actual POSIX requirement is that a 
read which occurs while a write is in progress cannot see a partially-completed 
write.  A system crash would tend to stop any writes in progress, so this 
particular requirement doesn't seem to apply.  :-)

> Update-in-place file systems can certainly support
> large-than-disk-sector write atomicity - they just
> have to use something like a transaction to do it.

True ... I don't know of any which do, but they could.  Maybe I should have 
said "update-in-place file systems which do not also write data to a separate 
log" to be more accurate....

Anton
 
 
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