linux-kernel - Re: [PATCH 2/2] treewide: Use sysfs_bin_attr_simple

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Date: Wed, 22 May 2024 19:51:35 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: Lukas Wunner <lukas@...ner.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	linux-kernel@...r.kernel.org, Michael Ellerman <mpe@...erman.id.au>,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	Jean Delvare <jdelvare@...e.com>, Ard Biesheuvel <ardb@...nel.org>,
	linux-efi@...r.kernel.org, Zhenyu Wang <zhenyuw@...ux.intel.com>,
	Zhi Wang <zhi.wang.linux@...il.com>,
	intel-gvt-dev@...ts.freedesktop.org,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	linux-pm@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>,
	linux-modules@...r.kernel.org
Subject: Re: [PATCH 2/2] treewide: Use sysfs_bin_attr_simple_read() helper

Hi,

On Sat, Apr 06, 2024 at 03:52:02PM +0200, Lukas Wunner wrote:
> Deduplicate ->read() callbacks of bin_attributes which are backed by a
> simple buffer in memory:
> 
> Use the newly introduced sysfs_bin_attr_simple_read() helper instead,
> either by referencing it directly or by declaring such bin_attributes
> with BIN_ATTR_SIMPLE_RO() or BIN_ATTR_SIMPLE_ADMIN_RO().
> 
> Aside from a reduction of LoC, this shaves off a few bytes from vmlinux
> (304 bytes on an x86_64 allyesconfig).
> 
> No functional change intended.
> 

Not really; see below.

> Signed-off-by: Lukas Wunner <lukas@...ner.de>
> Acked-by: Michael Ellerman <mpe@...erman.id.au> (powerpc)
> ---
..
> index da79760..5193fae 100644
> --- a/init/initramfs.c
> +++ b/init/initramfs.c
> @@ -575,15 +575,7 @@ static int __init initramfs_async_setup(char *str)
>  #include <linux/initrd.h>
>  #include <linux/kexec.h>
>  
> -static ssize_t raw_read(struct file *file, struct kobject *kobj,
> -			struct bin_attribute *attr, char *buf,
> -			loff_t pos, size_t count)
> -{
> -	memcpy(buf, attr->private + pos, count);
> -	return count;
> -}
> -
> -static BIN_ATTR(initrd, 0440, raw_read, NULL, 0);
> +static BIN_ATTR(initrd, 0440, sysfs_bin_attr_simple_read, NULL, 0);
>  

sysfs_bin_attr_simple_read is only declared and available if CONFIG_SYSFS=y.
With m68k:m5208evb_defconfig + CONFIG_BLK_DEV_INITRD=y, this results in

/opt/buildbot/slave/qemu-m68k/build/init/initramfs.c:578:31:
	error: 'sysfs_bin_attr_simple_read' undeclared here (not in a function)

This happens because CONFIG_SYSFS=n and there is no dummy function for
sysfs_bin_attr_simple_read(). Presumably the problem will be seen for all
configurations with CONFIG_BLK_DEV_INITRD=y and CONFIG_SYSFS=n.

On a side note, init/initramfs.c does not directly include linux/sysfs.h.
I don't know if that might cause problems with other builds.

Guenter