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Date: Wed, 30 Jul 2025 18:02:15 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Michal Luczaj <mhal@rbox.co>
Cc: "David S. Miller" <davem@davemloft.net>, Eric Dumazet
 <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Simon Horman
 <horms@kernel.org>, Cong Wang <cong.wang@bytedance.com>, Tom Herbert
 <tom@herbertland.com>, netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] kcm: Fix splice support
Message-ID: <20250730180215.2ad7df72@kernel.org>
In-Reply-To: <20250725-kcm-splice-v1-1-9a725ad2ee71@rbox.co>
References: <20250725-kcm-splice-v1-1-9a725ad2ee71@rbox.co>
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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..