Re: New copyfile system call - discuss before LSF?

Eric Wong
2013-03-31T21:23:59Z

Pavel Machek <pavel@ucw.cz> wrote:
> Eric Wong wrote:
> > [1] my splice() annoyances:
> > * need to create/manage a pipe
> > * copy size limited by pipe size
> > * doesn't reduce userspace syscalls (just data copy overhead)
> > * easy to misuse and starve with blocking sockets + big buffers
> > * not many users, so bugs creep in (v3.7.8 was the first usable
> > version of the 3.7 series for TCP sockets)
>
> Could library be created to make it less annoying to use, and harder
> to misuse?

Maybe, but getting people to use the library would be the hard, too.
And a library would not reduce syscalls in the common case.

We already have current->splice_pipe for sendfile, so maybe splice can
be taught to transparently use that when neither FD is a pipe.

I also think a SPLICE_F_DONTWAIT flag might be necessary. It would be a
superset of SPLICE_F_NONBLOCK, but also act like MSG_DONTWAIT for the
non-pipe socket.

> splice man page does not mention pipe size limit...

It probably should. I think I discovered it by using it many years ago
and burned it into my mind.