Commit d3d76fbd authored by Thomas Weißschuh's avatar Thomas Weißschuh Committed by Greg Kroah-Hartman
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kernel/ksysfs.c: export kernel cpu byteorder 



Certain files in procfs are formatted in byteorder-dependent formats.
For example the IP addresses in /proc/net/udp.

When using emulation like qemu-user, applications are not guaranteed to
be using the same byteorder as the kernel.
Therefore the kernel needs to provide a way for applications to discover
the byteorder used in API-filesystems.
Using systemcalls is not enough because these are intercepted and
translated by the emulation.

Also this makes it easier for non-compiled applications like
shellscripts to discover the byteorder.

Signed-off-by: default avatarThomas Weißschuh <linux@weissschuh.net>
Link: https://lore.kernel.org/r/20221103152407.3348-1-linux@weissschuh.net


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 52c4d11f

Documentation/ABI/testing/sysfs-kernel-cpu_byteorder

0 → 100644
+12 −0
Original line number Diff line number Diff line 
What:		/sys/kernel/cpu_byteorder

Date:		February 2023

KernelVersion:	6.2

Contact:	Thomas Weißschuh <linux@weissschuh.net>

Description:

		The endianness of the running kernel.



		Access: Read



		Valid values:

			"little", "big"

Users:		util-linux

kernel/ksysfs.c

+18 −0
Original line number Diff line number Diff line
@@ -6,6 +6,7 @@ 
 * Copyright (C) 2004 Kay Sievers <kay.sievers@vrfy.org>

 */



#include <asm/byteorder.h>

#include <linux/kobject.h>

#include <linux/string.h>

#include <linux/sysfs.h>
@@ -20,6 +21,14 @@ 


#include <linux/rcupdate.h>	/* rcu_expedited and rcu_normal */



#if defined(__LITTLE_ENDIAN)

#define CPU_BYTEORDER_STRING	"little"

#elif defined(__BIG_ENDIAN)

#define CPU_BYTEORDER_STRING	"big"

#else

#error Unknown byteorder

#endif



#define KERNEL_ATTR_RO(_name) \

static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
@@ -34,6 +43,14 @@ static ssize_t uevent_seqnum_show(struct kobject *kobj, 
}

KERNEL_ATTR_RO(uevent_seqnum);



/* cpu byteorder */

static ssize_t cpu_byteorder_show(struct kobject *kobj,

				  struct kobj_attribute *attr, char *buf)

{

	return sysfs_emit(buf, "%s\n", CPU_BYTEORDER_STRING);

}

KERNEL_ATTR_RO(cpu_byteorder);



#ifdef CONFIG_UEVENT_HELPER

/* uevent helper program, used during early boot */

static ssize_t uevent_helper_show(struct kobject *kobj,
@@ -215,6 +232,7 @@ EXPORT_SYMBOL_GPL(kernel_kobj); 
static struct attribute * kernel_attrs[] = {

	&fscaps_attr.attr,

	&uevent_seqnum_attr.attr,

	&cpu_byteorder_attr.attr,

#ifdef CONFIG_UEVENT_HELPER

	&uevent_helper_attr.attr,

#endif