On Fri, 5 Jun 2026 17:20:34 +0200
Stefan Metzmacher [off-list ref] wrote:

Hi David,

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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