Re: [PATCH v2 4/4] serial: Add kserial_rs485 to avoid wasted space due to .padding

From: Jiri Slaby <jirislaby@kernel.org>
To: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	linux-serial@vger.kernel.org,
	"Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Vladimir Zapolskiy" <vz@mleia.com>,
	"Russell King" <linux@armlinux.org.uk>,
	"Richard Genoud" <richard.genoud@gmail.com>,
	"Nicolas Ferre" <nicolas.ferre@microchip.com>,
	"Alexandre Belloni" <alexandre.belloni@bootlin.com>,
	"Claudiu Beznea" <claudiu.beznea@microchip.com>,
	"Shawn Guo" <shawnguo@kernel.org>,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"Pengutronix Kernel Team" <kernel@pengutronix.de>,
	"Fabio Estevam" <festevam@gmail.com>,
	"NXP Linux Team" <linux-imx@nxp.com>,
	"Maxime Coquelin" <mcoquelin.stm32@gmail.com>,
	"Alexandre Torgue" <alexandre.torgue@foss.st.com>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-stm32@st-md-mailman.stormreply.com
Cc: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Subject: Re: [PATCH v2 4/4] serial: Add kserial_rs485 to avoid wasted space due to .padding
Date: Tue, 30 Aug 2022 10:01:59 +0200	[thread overview]
Message-ID: <1068ad37-d80c-6e63-6cd9-6ecf6c256d46@kernel.org> (raw)
In-Reply-To: <20220830072956.3630-5-ilpo.jarvinen@linux.intel.com>

On 30. 08. 22, 9:29, Ilpo Järvinen wrote:
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -31,6 +31,29 @@ struct serial_struct;
...
> + * Must match with struct serial_rs485 in include/uapi/linux/serial.h excluding
> + * the padding.

Have you considered BUILD_BUG_ON() checks with few offset_of()s to 
enforce the above?

> +struct kserial_rs485 {
> +	__u32	flags;
> +	__u32	delay_rts_before_send;
> +	__u32	delay_rts_after_send;
> +	struct {
> +		__u8    addr_recv;
> +		__u8    addr_dest;
> +	};
> +};

thanks,
-- 
js
suse labs

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