Re: [patch v3] splice: fix race with page invalidation

Linus Torvalds
2008-07-31T00:58:27Z

On Wed, 30 Jul 2008, Linus Torvalds wrote:
>
> Personally, I think the right approach is to just realize that splice() is
> _not_ a write() system call, and never will be. If you need synchronous
> writing, you simply shouldn't use splice().

Side note: in-kernel users could probably do somethign about this. IOW, if
there's some in-kernel usage (and yes, knfsd would be a prime example),
that one may actually be able to do things that a _user_level user of
splice() could never do.

That includes things like getting the inode semaphore over a write (so
that you can guarantee that pages that are in flight are not modified,
except again possibly by other mmap users), and/or a per-page callback for
when splice() is done with a page (so that you could keep the page locked
while it's getting spliced, for example).

And no, we don't actually have that either, of course.

Linus