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From:   David Howells <dhowells@redhat.com>
In-Reply-To: <7854000d2ce5ac32b75782a7c4574f25a11b573d.1689757133.git.jstancek@redhat.com>
References: <7854000d2ce5ac32b75782a7c4574f25a11b573d.1689757133.git.jstancek@redhat.com>
To:     Jan Stancek <jstancek@redhat.com>
Cc:     dhowells@redhat.com, kuba@kernel.org,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        brauner@kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCH] splice, net: Fix splice_to_socket() for O_NONBLOCK socket
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Content-ID: <64433.1690193532.1@warthog.procyon.org.uk>
Date:   Mon, 24 Jul 2023 11:12:12 +0100
Message-ID: <64434.1690193532@warthog.procyon.org.uk>
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Jan Stancek <jstancek@redhat.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