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

From: David Laight <[email-masked]>
Date: Sat, 6 Jun 2026 11:22:52 +0100

On Fri, 5 Jun 2026 17:20:34 +0200
Stefan Metzmacher <[email-masked]> wrote:

> Hi David,
> 
> >>> So sendfile() as a concept (whether you use combinations of splice()
> >>> system calls or the sendfile system call itsefl) isn't necessarily
> >>> only about the zero-copy, it's really also about avoiding the user
> >>> space memory management.  
> >>
> >> I don't think so. Ok, maybe for webservers just serving tiny
> >> html files, that's true. But for me with Samba it's really the
> >> copy_to/from_iter() that is the major factor.  
> > 
> > Is that copy also doing the ip checksum?  
> 
> Not in my tests. I guess there's offload in the network hardware
> for this.

There will be, it is just whether the syscall checksum is actually
being suppressed.

-- David

> 
> At least at the syscall layer of sendmsg() there's no checksuming
> happening.
> 
> metze
>