Re: filesystem transactions API

[Jamie Lokier <jamie@shareable.org>]

Artem B. Bityuckiy wrote:
> Jamie Lokier wrote:
> >I think I've wanted something like that for _years_ in unix.
> >
> >It's an old, old idea, and I've often wondered why we haven't implemented 
> >it.
> >
> 
> I thought it is possible to rather easily to implement this on top
> of non-transactional FS (albeit I didn't try) and there is no need
> to overcomplicate an FS. Just implement a specialized user-space
> library and utilize it.

No.  A transaction means that _all_ processes will see the whole
transaction or not.

It does _not_ mean that only a subset of programs, which happen to
link with a particular user-space library, will see it or not.

For example, you can use transactions for distro package management: a
whole update of a package would be a single transaction, so that at no
time does any program see an inconsistent set of files.  See why
_every_ process in the system must have the same view?

[ If you meant that you can implement it with a user-space library
that every process in the system links to, that's true.  But it would
rather misses the point of having filesystems in the kernel at all :) ]

-- Jamie