On Wed, May 31, 2023 at 01:45:24PM +0100, David Howells wrote:

It is necessary to allow MSG_SENDPAGE_* to be passed into ->sendmsg() to
allow sendmsg(MSG_SPLICE_PAGES) to replace ->sendpage().  Unblocking them
in the network protocol, however, allows these flags to be passed in by
userspace too[1].

Fix this by marking MSG_SENDPAGE_NOPOLICY, MSG_SENDPAGE_NOTLAST and
MSG_SENDPAGE_DECRYPTED as internal flags, which causes sendmsg() to object
if they are passed to sendmsg() by userspace.  Network protocol ->sendmsg()
implementations can then allow them through.

Note that it should be possible to remove MSG_SENDPAGE_NOTLAST once
sendpage is removed as a whole slew of pages will be passed in in one go by

Hi David,

on the off-chance that you need to respin for some other reason:

	s/in in/in/

splice through sendmsg, with MSG_MORE being set if it has more data waiting
in the pipe.

...