linux-kernel - Re: [PATCH] splice, net: Fix splice_to_socket() for O

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Message-ID: <CAASaF6yKxWaW6me0Y+vSEo0qUm_LTyL5CPVka75EPg_yq4MO9g@mail.gmail.com>
Date:   Mon, 24 Jul 2023 16:51:11 +0200
From:   Jan Stancek <jstancek@...hat.com>
To:     David Howells <dhowells@...hat.com>
Cc:     kuba@...nel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, brauner@...nel.org,
        viro@...iv.linux.org.uk
Subject: Re: [PATCH] splice, net: Fix splice_to_socket() for O_NONBLOCK socket

On Mon, Jul 24, 2023 at 12:12 PM David Howells <dhowells@...hat.com> wrote:
>
> Jan Stancek <jstancek@...hat.com> 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.