sendfile is also not necessarily zero-copy: https://svnweb.freebsd.org/base?view=revision&revision=255608 https://svnweb.freebsd.org/base?view=revision&revision

sendfile is also not necessarily zero-copy: https://svnweb.freebsd.org/base?view=revision&revision=255608 https://svnweb.freebsd.org/base?view=revision&revision=25560... https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?id=485ddb4b9741bafb70b22e5c1f9b4f37dc3e85bd https://git.kernel.org/cgit/linux/kernel/git/stable/linux-st... (sendfile calls splice; the splice manpage also states that it might copy instead of move pages.) That said, it equates to a single kernel-to-kernel copy instead of a kernel-to-userspace plus a userspace-to-kernel copy as in the read/write case.