David Howells wrote:

Willem de Bruijn [off-list ref] wrote:

quoted

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.