netdev - Re: [PATCH v2 net-next] ipv4: Convert ->flowi4_tos to dscp

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Message-ID: <aK1MnoX4eNw4Ql-1@shredder>
Date: Tue, 26 Aug 2025 08:56:46 +0300
From: Ido Schimmel <idosch@...dia.com>
To: Guillaume Nault <gnault@...hat.com>
Cc: David Miller <davem@...emloft.net>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
	netdev@...r.kernel.org, Simon Horman <horms@...nel.org>,
	Taehee Yoo <ap420073@...il.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Saeed Mahameed <saeedm@...dia.com>,
	Leon Romanovsky <leon@...nel.org>, Tariq Toukan <tariqt@...dia.com>,
	Mark Bloch <mbloch@...dia.com>,
	Edward Cree <ecree.xilinx@...il.com>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	Harald Welte <laforge@...monks.org>,
	David Ahern <dsahern@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Jozsef Kadlecsik <kadlec@...filter.org>,
	Florian Westphal <fw@...len.de>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
	Xin Long <lucien.xin@...il.com>
Subject: Re: [PATCH v2 net-next] ipv4: Convert ->flowi4_tos to dscp_t.

On Mon, Aug 25, 2025 at 03:37:43PM +0200, Guillaume Nault wrote:
> Convert the ->flowic_tos field of struct flowi_common from __u8 to
> dscp_t, rename it ->flowic_dscp and propagate these changes to struct
> flowi and struct flowi4.
> 
> We've had several bugs in the past where ECN bits could interfere with
> IPv4 routing, because these bits were not properly cleared when setting
> ->flowi4_tos. These bugs should be fixed now and the dscp_t type has
> been introduced to ensure that variables carrying DSCP values don't
> accidentally have any ECN bits set. Several variables and structure
> fields have been converted to dscp_t already, but the main IPv4 routing
> structure, struct flowi4, is still using a __u8. To avoid any future
> regression, this patch converts it to dscp_t.
> 
> There are many users to convert at once. Fortunately, around half of
> ->flowi4_tos users already have a dscp_t value at hand, which they
> currently convert to __u8 using inet_dscp_to_dsfield(). For all of
> these users, we just need to drop that conversion.
> 
> But, although we try to do the __u8 <-> dscp_t conversions at the
> boundaries of the network or of user space, some places still store
> TOS/DSCP variables as __u8 in core networking code. Those can hardly be
> converted either because the data structure is part of UAPI or because
> the same variable or field is also used for handling ECN in other parts
> of the code. In all of these cases where we don't have a dscp_t
> variable at hand, we need to use inet_dsfield_to_dscp() when
> interacting with ->flowi4_dscp.
> 
> Changes since v1:
>   * Fix space alignment in __bpf_redirect_neigh_v4() (Ido).
> 
> Signed-off-by: Guillaume Nault <gnault@...hat.com>

Reviewed-by: Ido Schimmel <idosch@...dia.com>