Re: [PATCH 0/3] vmsplice: make vmsplice a trivial wrapper for preadv2/pwritev2

On Thu, 4 Jun 2026 at 08:53, Willy Tarreau <[email protected]> wrote:
>
> > It looks like you're actually doing exactly the thing that I thought
> > was crazy and wouldn't even work reliably: you change the
> > common_response[] contents dynamically *after* the vmsplice, and
> > depend on the fact that changing it in user space changes the buffer
> > in the pipe too.
>
> No no, it's definitely not doing that (or it's a bug, but it's not
> supposed to happen). I'm perfectly aware that one must definitely not
> do that, and it's a guarantee the user of vmsplice() must provide.

Whew, good.

In that case, can you just try the vmsplice patch series (Christian
already found a bug, but I don't think it will necessarily matter in
practice - famous last words) and that test patch of mine, and see if
it all (a) works for you and (b) if you have any numbers for
performance that would be *great*.

There aren't many obvious splice users out there, and even if they
were to exist they are typically specialized enough that you have to
have a real use case to then tell if the patches make a difference in
real life or not.

So you testing that thing would seem to be a great first test of
whether any of this is realistic..

               Linus