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authorThomas Weißschuh <linux@weissschuh.net>2022-11-03 16:24:07 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2022-11-10 19:07:31 +0100
commitd3d76fbde1c456a6d19991baa99ea8c2d6e6696f (patch)
tree1d8439184733609465b51d19a761613b91f2fe84 /kernel/ksysfs.c
parent52c4d11f1dce60453ab2a75fd7103118cedb2b58 (diff)
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: Thomas Weißschuh <linux@weissschuh.net> Link: https://lore.kernel.org/r/20221103152407.3348-1-linux@weissschuh.net Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel/ksysfs.c')
-rw-r--r--kernel/ksysfs.c18
1 files changed, 18 insertions, 0 deletions
diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
index 65dba9076f31..2df00b789b90 100644
--- a/kernel/ksysfs.c
+++ b/kernel/ksysfs.c
@@ -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