Re: [PATCH] splice, net: Fix splice_to_socket() for O_NONBLOCK socket

[Jan Stancek]

On Mon, Jul 24, 2023 at 12:12 PM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> Jan Stancek <jstancek@xxxxxxxxxx> wrote:
>
> > LTP sendfile07 [1], which expects sendfile() to return EAGAIN when
> > transferring data from regular file to a "full" O_NONBLOCK socket,
> > started failing after commit 2dc334f1a63a ("splice, net: Use
> > sendmsg(MSG_SPLICE_PAGES) rather than ->sendpage()").
> > sendfile() no longer immediately returns, but now blocks.
> >
> > Removed sock_sendpage() handled this case by setting a MSG_DONTWAIT
> > flag, fix new splice_to_socket() to do the same for O_NONBLOCK sockets.
>
> Does this actually work correctly in all circumstances?
>
> The problem might come if you have a splice from a non-rewindable source
> through a temporary pipe (eg. sendfile() using splice_direct_to_actor()).

I assumed this was safe, since sendfile / splice_direct_to_actor()
requires input to be seekable.