From d3d76fbde1c456a6d19991baa99ea8c2d6e6696f Mon Sep 17 00:00:00 2001 From: Thomas Weißschuh Date: Thu, 3 Nov 2022 16:24:07 +0100 Subject: kernel/ksysfs.c: export kernel cpu byteorder MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Link: https://lore.kernel.org/r/20221103152407.3348-1-linux@weissschuh.net Signed-off-by: Greg Kroah-Hartman --- kernel/ksysfs.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'kernel/ksysfs.c') 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 */ +#include #include #include #include @@ -20,6 +21,14 @@ #include /* 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 -- cgit v1.2.3