netdev - Re: [PATCH net] kcm: Fix splice support

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Message-ID: <20250730180215.2ad7df72@kernel.org>
Date: Wed, 30 Jul 2025 18:02:15 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Michal Luczaj <mhal@...x.co>
Cc: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman
 <horms@...nel.org>, Cong Wang <cong.wang@...edance.com>, Tom Herbert
 <tom@...bertland.com>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] kcm: Fix splice support

On Fri, 25 Jul 2025 12:33:04 +0200 Michal Luczaj wrote:
> Flags passed in for splice() syscall should not end up in
> skb_recv_datagram(). As SPLICE_F_NONBLOCK == MSG_PEEK, kernel gets
> confused: skb isn't unlinked from a receive queue, while strp_msg::offset
> and strp_msg::full_len are updated.
> 
> Unbreak the logic a bit more by mapping both O_NONBLOCK and
> SPLICE_F_NONBLOCK to MSG_DONTWAIT. This way we align with man splice(2) in
> regard to errno EAGAIN:
> 
>    SPLICE_F_NONBLOCK was specified in flags or one of the file descriptors
>    had been marked as nonblocking (O_NONBLOCK), and the operation would
>    block.

Coincidentally looks like we're not honoring

	sock->file->f_flags & O_NONBLOCK 

in TLS..