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

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Date:   Mon, 24 Jul 2023 11:12:12 +0100
From:   David Howells <dhowells@...hat.com>
To:     Jan Stancek <jstancek@...hat.com>
Cc:     dhowells@...hat.com, 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

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()).

David