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SubjectRe: [RFC PATCH 03/28] tcp: Support MSG_SPLICE_PAGES
David Howells wrote:
> Willem de Bruijn <willemdebruijn.kernel@gmail.com> wrote:
>
> > The commit message mentions MSG_SPLICE_PAGES as an internal flag.
> >
> > It can be passed from userspace. The code anticipates that and checks
> > preconditions.
>
> Should I add a separate field in the in-kernel msghdr struct for such internal
> flags? That would also avoid putting an internal flag in the same space as
> the uapi flags.

That would work, if no cost to common paths that don't need it.

A not very pretty alternative would be to add an an extra arg to each
sendmsg handler that is used only when called from sendpage.

There are a few other internal MSG_.. flags, such as
MSG_SENDPAGE_NOPOLICY. Those are all limited to sendpage, and ignored
in sendmsg, I think. Which would explain why it was clearly safe to
add them.

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