[PATCH V5 14/30] csky: User access

Guo Ren
2018-09-24T14:38:35Z

This patch adds "user access from kernel" codes.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
---
arch/csky/include/asm/uaccess.h | 399 ++++++++++++++++++++++++++++++++++++++++
arch/csky/lib/usercopy.c | 271 +++++++++++++++++++++++++++
2 files changed, 670 insertions(+)
create mode 100644 arch/csky/include/asm/uaccess.h
create mode 100644 arch/csky/lib/usercopy.c

diff --git a/arch/csky/include/asm/uaccess.h b/arch/csky/include/asm/uaccess.h
new file mode 100644
index 0000000..b927391
--- /dev/null
+++ b/arch/csky/include/asm/uaccess.h
@@ -0,0 +1,399 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#ifndef __ASM_CSKY_UACCESS_H
+#define __ASM_CSKY_UACCESS_H
+
+/*
+ * User space memory access functions
+ */
+#include <linux/compiler.h>
+#include <linux/errno.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/string.h>
+#include <linux/version.h>
+#include <asm/segment.h>
+
+#define VERIFY_READ 0
+#define VERIFY_WRITE 1
+
+static inline int access_ok(int type, const void * addr, unsigned long size)
+{
+ return (((unsigned long)addr < current_thread_info()->addr_limit.seg) &&
+ ((unsigned long)(addr + size) < current_thread_info()->addr_limit.seg));
+}
+
+static inline int verify_area(int type, const void * addr, unsigned long size)
+{
+ return access_ok(type, addr, size) ? 0 : -EFAULT;
+}
+
+#define __addr_ok(addr) (access_ok(VERIFY_READ, addr,0))
+
+extern int __put_user_bad(void);
+
+/*
+ * Tell gcc we read from memory instead of writing: this is because
+ * we do not write to any memory gcc knows about, so there are no
+ * aliasing issues.
+ */
+
+/*
+ * These are the main single-value transfer routines. They automatically
+ * use the right size if we just have the right pointer type.
+ *
+ * This gets kind of ugly. We want to return _two_ values in "get_user()"
+ * and yet we don't want to do any pointers, because that is too much
+ * of a performance impact. Thus we have a few rather ugly macros here,
+ * and hide all the ugliness from the user.
+ *
+ * The "__xxx" versions of the user access functions are versions that
+ * do not verify the address space, that must have been done previously
+ * with a separate "access_ok()" call (this is used when we do multiple
+ * accesses to the same area of user memory).
+ *
+ * As we use the same address space for kernel and user data on
+ * Ckcore, we can just do these as direct assignments. (Of course, the
+ * exception handling means that it's no longer "just"...)
+ */
+
+#define put_user(x,ptr) \
+ __put_user_check((x), (ptr), sizeof(*(ptr)))
+
+#define __put_user(x,ptr) \
+ __put_user_nocheck((x), (ptr), sizeof(*(ptr)))
+
+#define __ptr(x) ((unsigned long *)(x))
+
+#define get_user(x,ptr) \
+ __get_user_check((x), (ptr), sizeof(*(ptr)))
+
+#define __get_user(x,ptr) \
+ __get_user_nocheck((x), (ptr), sizeof(*(ptr)))
+
+#define __put_user_nocheck(x, ptr, size) \
+({ \
+ long __pu_err=0; \
+ typeof(*(ptr)) *__pu_addr = (ptr); \
+ typeof(*(ptr)) __pu_val = (typeof(*(ptr)))(x); \
+ if(__pu_addr){ \
+ __put_user_size(__pu_val, (__pu_addr), (size), __pu_err); \
+ } \
+ __pu_err; \
+})
+
+#define __put_user_check(x,ptr,size) \
+({ \
+ long __pu_err = -EFAULT; \
+ typeof(*(ptr)) *__pu_addr = (ptr); \
+ typeof(*(ptr)) __pu_val = (typeof(*(ptr)))(x); \
+ if (access_ok(VERIFY_WRITE, __pu_addr, size) && __pu_addr) \
+ __put_user_size(__pu_val, __pu_addr, (size), __pu_err); \
+ __pu_err; \
+})
+
+#define __put_user_size(x,ptr,size,retval) \
+do { \
+ retval = 0; \
+ switch (size) { \
+ case 1: __put_user_asm_b(x, ptr, retval); break; \
+ case 2: __put_user_asm_h(x, ptr, retval); break; \
+ case 4: __put_user_asm_w(x, ptr, retval); break; \
+ case 8: __put_user_asm_64(x, ptr, retval); break; \
+ default: __put_user_bad(); \
+ } \
+} while (0)
+
+/*
+ * We don't tell gcc that we are accessing memory, but this is OK
+ * because we do not write to any memory gcc knows about, so there
+ * are no aliasing issues.
+ *
+ * Note that PC at a fault is the address *after* the faulting
+ * instruction.
+ */
+#define __put_user_asm_b(x, ptr, err) \
+do{ \
+ int errcode; \
+ asm volatile( \
+ "1: stb %1, (%2,0) \n" \
+ " br 3f \n" \
+ "2: mov %0, %3 \n" \
+ " br 3f \n" \
+ ".section __ex_table,\"a\" \n" \
+ ".align 2 \n" \
+ ".long 1b,2b \n" \
+ ".previous \n" \
+ "3: \n" \
+ : "=r"(err), "=r"(x), "=r"(ptr), "=r"(errcode) \
+ : "0"(err), "1"(x), "2"(ptr), "3"(-EFAULT) \
+ : "memory"); \
+}while(0)
+
+#define __put_user_asm_h(x, ptr, err) \
+do{ \
+ int errcode; \
+ asm volatile( \
+ "1: sth %1, (%2,0) \n" \
+ " br 3f \n" \
+ "2: mov %0, %3 \n" \
+ " br 3f \n" \
+ ".section __ex_table,\"a\" \n" \
+ ".align 2 \n" \
+ ".long 1b,2b \n" \
+ ".previous \n" \
+ "3: \n" \
+ :"=r"(err), "=r"(x), "=r"(ptr), "=r"(errcode) \
+ :"0"(err), "1"(x), "2"(ptr), "3"(-EFAULT) \
+ : "memory"); \
+}while(0)
+
+#define __put_user_asm_w(x, ptr, err) \
+do{ \
+ int errcode; \
+ asm volatile( \
+ "1: stw %1, (%2,0) \n" \
+ " br 3f \n" \
+ "2: mov %0, %3 \n" \
+ " br 3f \n" \
+ ".section __ex_table,\"a\" \n" \
+ ".align 2 \n" \
+ ".long 1b,2b \n" \
+ ".previous \n" \
+ "3: \n" \
+ :"=r"(err), "=r"(x), "=r"(ptr), "=r"(errcode) \
+ :"0"(err), "1"(x), "2"(ptr), "3"(-EFAULT) \
+ : "memory"); \
+}while(0)
+
+#define __put_user_asm_64(x, ptr, err) \
+do{ \
+ int tmp; \
+ int errcode; \
+ typeof(*(ptr)) src = ( typeof(*(ptr)))x; \
+ typeof(*(ptr)) *psrc = &src; \
+ \
+ asm volatile( \
+ " ldw %3, (%1, 0) \n" \
+ "1: stw %3, (%2, 0) \n" \
+ " ldw %3, (%1, 4) \n" \
+ "2: stw %3, (%2, 4) \n" \
+ " br 4f \n" \
+ "3: mov %0, %4 \n" \
+ " br 4f \n" \
+ ".section __ex_table, \"a\" \n" \
+ ".align 2 \n" \
+ ".long 1b, 3b \n" \
+ ".long 2b, 3b \n" \
+ ".previous \n" \
+ "4: \n" \
+ :"=r"(err),"=r"(psrc),"=r"(ptr),"=r"(tmp),"=r"(errcode) \
+ : "0"(err), "1"(psrc), "2"(ptr), "3"(0), "4"(-EFAULT) \
+ : "memory" ); \
+}while (0)
+
+#define __get_user_nocheck(x, ptr, size) \
+({ \
+ long __gu_err; \
+ __get_user_size(x, (ptr), (size), __gu_err); \
+ __gu_err; \
+})
+
+#define __get_user_check(x, ptr, size) \
+({ \
+ int __gu_err = -EFAULT; \
+ const __typeof__(*(ptr)) __user * __gu_ptr = (ptr); \
+ if (access_ok(VERIFY_READ, __gu_ptr, size) && __gu_ptr) \
+ __get_user_size(x, __gu_ptr, (size), __gu_err); \
+ __gu_err; \
+})
+
+#define __get_user_size(x, ptr, size, retval) \
+do { \
+ switch (size) { \
+ case 1: __get_user_asm_common((x),ptr,"ldb",retval);break;\
+ case 2: __get_user_asm_common((x),ptr,"ldh",retval);break;\
+ case 4: __get_user_asm_common((x),ptr,"ldw",retval);break;\
+ default: \
+ x=0; \
+ (retval) = __get_user_bad(); \
+ } \
+} while (0)
+
+#define __get_user_asm_common(x, ptr, ins, err) \
+do{ \
+ int errcode; \
+ asm volatile( \
+ "1: " ins " %1, (%4,0) \n" \
+ " br 3f \n" \
+ /* Fix up codes */ \
+ "2: mov %0, %2 \n" \
+ " movi %1, 0 \n" \
+ " br 3f \n" \
+ ".section __ex_table,\"a\" \n" \
+ ".align 2 \n" \
+ ".long 1b,2b \n" \
+ ".previous \n" \
+ "3: \n" \
+ :"=r"(err), "=r"(x), "=r"(errcode) \
+ :"0"(0), "r"(ptr), "2"(-EFAULT) \
+ : "memory"); \
+}while(0)
+
+extern int __get_user_bad(void);
+
+#define __copy_user(to, from, n) \
+do{ \
+ int w0, w1, w2, w3; \
+ asm volatile( \
+ "0: cmpnei %1, 0 \n" \
+ " bf 8f \n" \
+ " mov %3, %1 \n" \
+ " or %3, %2 \n" \
+ " andi %3, 3 \n" \
+ " cmpnei %3, 0 \n" \
+ " bf 1f \n" \
+ " br 5f \n" \
+ "1: cmplti %0, 16 \n" /* 4W */ \
+ " bt 3f \n" \
+ " ldw %3, (%2, 0) \n" \
+ " ldw %4, (%2, 4) \n" \
+ " ldw %5, (%2, 8) \n" \
+ " ldw %6, (%2, 12) \n" \
+ "2: stw %3, (%1, 0) \n" \
+ "9: stw %4, (%1, 4) \n" \
+ "10: stw %5, (%1, 8) \n" \
+ "11: stw %6, (%1, 12) \n" \
+ " addi %2, 16 \n" \
+ " addi %1, 16 \n" \
+ " subi %0, 16 \n" \
+ " br 1b \n" \
+ "3: cmplti %0, 4 \n" /* 1W */ \
+ " bt 5f \n" \
+ " ldw %3, (%2, 0) \n" \
+ "4: stw %3, (%1, 0) \n" \
+ " addi %2, 4 \n" \
+ " addi %1, 4 \n" \
+ " subi %0, 4 \n" \
+ " br 3b \n" \
+ "5: cmpnei %0, 0 \n" /* 1B */ \
+ " bf 8f \n" \
+ " ldb %3, (%2, 0) \n" \
+ "6: stb %3, (%1, 0) \n" \
+ " addi %2, 1 \n" \
+ " addi %1, 1 \n" \
+ " subi %0, 1 \n" \
+ " br 5b \n" \
+ "7: br 8f \n" \
+ ".section __ex_table, \"a\" \n" \
+ ".align 2 \n" \
+ ".long 2b, 7b \n" \
+ ".long 9b, 7b \n" \
+ ".long 10b, 7b \n" \
+ ".long 11b, 7b \n" \
+ ".long 4b, 7b \n" \
+ ".long 6b, 7b \n" \
+ ".previous \n" \
+ "8: \n" \
+ : "=r"(n), "=r"(to), "=r"(from), "=r"(w0), \
+ "=r"(w1), "=r"(w2), "=r"(w3) \
+ : "0"(n), "1"(to), "2"(from) \
+ : "memory" ); \
+} while (0)
+
+#define __copy_user_zeroing(to, from, n) \
+do{ \
+ int tmp; \
+ int nsave; \
+ asm volatile( \
+ "0: cmpnei %1, 0 \n" \
+ " bf 7f \n" \
+ " mov %3, %1 \n" \
+ " or %3, %2 \n" \
+ " andi %3, 3 \n" \
+ " cmpnei %3, 0 \n" \
+ " bf 1f \n" \
+ " br 5f \n" \
+ "1: cmplti %0, 16 \n" \
+ " bt 3f \n" \
+ "2: ldw %3, (%2, 0) \n" \
+ "10: ldw %4, (%2, 4) \n" \
+ " stw %3, (%1, 0) \n" \
+ " stw %4, (%1, 4) \n" \
+ "11: ldw %3, (%2, 8) \n" \
+ "12: ldw %4, (%2, 12) \n" \
+ " stw %3, (%1, 8) \n" \
+ " stw %4, (%1, 12) \n" \
+ " addi %2, 16 \n" \
+ " addi %1, 16 \n" \
+ " subi %0, 16 \n" \
+ " br 1b \n" \
+ "3: cmplti %0, 4 \n" \
+ " bt 5f \n" \
+ "4: ldw %3, (%2, 0) \n" \
+ " stw %3, (%1, 0) \n" \
+ " addi %2, 4 \n" \
+ " addi %1, 4 \n" \
+ " subi %0, 4 \n" \
+ " br 3b \n" \
+ "5: cmpnei %0, 0 \n" \
+ " bf 7f \n" \
+ "6: ldb %3, (%2, 0) \n" \
+ " stb %3, (%1, 0) \n" \
+ " addi %2, 1 \n" \
+ " addi %1, 1 \n" \
+ " subi %0, 1 \n" \
+ " br 5b \n" \
+ "8: mov %3, %0 \n" \
+ " movi %4, 0 \n" \
+ "9: stb %4, (%1, 0) \n" \
+ " addi %1, 1 \n" \
+ " subi %3, 1 \n" \
+ " cmpnei %3, 0 \n" \
+ " bt 9b \n" \
+ " br 7f \n" \
+ ".section __ex_table, \"a\" \n" \
+ ".align 2 \n" \
+ ".long 2b, 8b \n" \
+ ".long 10b, 8b \n" \
+ ".long 11b, 8b \n" \
+ ".long 12b, 8b \n" \
+ ".long 4b, 8b \n" \
+ ".long 6b, 8b \n" \
+ ".previous \n" \
+ "7: \n" \
+ : "=r"(n), "=r"(to), "=r"(from), "=r"(nsave), \
+ "=r"(tmp) \
+ : "0"(n), "1"(to), "2"(from) \
+ : "memory" ); \
+} while (0)
+
+unsigned long raw_copy_from_user(void *to, const void *from, unsigned long n);
+unsigned long raw_copy_to_user(void *to, const void *from, unsigned long n);
+
+unsigned long clear_user(void *to, unsigned long n);
+unsigned long __clear_user(void __user *to, unsigned long n);
+
+long strncpy_from_user(char *dst, const char *src, long count);
+long __strncpy_from_user(char *dst, const char *src, long count);
+
+/*
+ * Return the size of a string (including the ending 0)
+ *
+ * Return 0 on exception, a value greater than N if too long
+ */
+long strnlen_user(const char *src, long n);
+
+#define strlen_user(str) strnlen_user(str, 32767)
+
+struct exception_table_entry
+{
+ unsigned long insn;
+ unsigned long nextinsn;
+};
+
+extern int fixup_exception(struct pt_regs *regs);
+
+#endif /* __ASM_CSKY_UACCESS_H */
diff --git a/arch/csky/lib/usercopy.c b/arch/csky/lib/usercopy.c
new file mode 100644
index 0000000..576386e
--- /dev/null
+++ b/arch/csky/lib/usercopy.c
@@ -0,0 +1,271 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2018 Hangzhou C-SKY Microsystems co.,ltd.
+
+#include <linux/uaccess.h>
+#include <linux/types.h>
+
+unsigned long
+raw_copy_from_user(
+ void *to,
+ const void *from,
+ unsigned long n)
+{
+ if (access_ok(VERIFY_READ, from, n))
+ __copy_user_zeroing(to,from,n);
+ else
+ memset(to,0, n);
+ return n;
+}
+EXPORT_SYMBOL(raw_copy_from_user);
+
+unsigned long
+raw_copy_to_user(
+ void *to,
+ const void *from,
+ unsigned long n)
+{
+ if (access_ok(VERIFY_WRITE, to, n))
+ __copy_user(to,from,n);
+ return n;
+}
+EXPORT_SYMBOL(raw_copy_to_user);
+
+
+/*
+ * copy a null terminated string from userspace.
+ */
+#define __do_strncpy_from_user(dst,src,count,res) \
+do{ \
+ int tmp; \
+ long faultres; \
+ asm volatile( \
+ " cmpnei %3, 0 \n" \
+ " bf 4f \n" \
+ "1: cmpnei %1, 0 \n" \
+ " bf 5f \n" \
+ "2: ldb %4, (%3, 0) \n" \
+ " stb %4, (%2, 0) \n" \
+ " cmpnei %4, 0 \n" \
+ " bf 3f \n" \
+ " addi %3, 1 \n" \
+ " addi %2, 1 \n" \
+ " subi %1, 1 \n" \
+ " br 1b \n" \
+ "3: subu %0, %1 \n" \
+ " br 5f \n" \
+ "4: mov %0, %5 \n" \
+ " br 5f \n" \
+ ".section __ex_table, \"a\" \n" \
+ ".align 2 \n" \
+ ".long 2b, 4b \n" \
+ ".previous \n" \
+ "5: \n" \
+ :"=r"(res),"=r"(count),"=r"(dst),"=r"(src), "=r"(tmp),"=r"(faultres) \
+ : "5"(-EFAULT),"0"(count), "1"(count), "2"(dst),"3"(src) \
+ : "memory" ); \
+} while(0)
+
+/*
+ * __strncpy_from_user: - Copy a NUL terminated string from userspace, with less checking.
+ * @dst: Destination address, in kernel space. This buffer must be at
+ * least @count bytes long.
+ * @src: Source address, in user space.
+ * @count: Maximum number of bytes to copy, including the trailing NUL.
+ *
+ * Copies a NUL-terminated string from userspace to kernel space.
+ * Caller must check the specified block with access_ok() before calling
+ * this function.
+ *
+ * On success, returns the length of the string (not including the trailing
+ * NUL).
+ *
+ * If access to userspace fails, returns -EFAULT (some data may have been
+ * copied).
+ *
+ * If @count is smaller than the length of the string, copies @count bytes
+ * and returns @count.
+ */
+long
+__strncpy_from_user(
+ char *dst,
+ const char *src,
+ long count)
+{
+ long res;
+ __do_strncpy_from_user(dst, src, count, res);
+ return res;
+}
+EXPORT_SYMBOL(__strncpy_from_user);
+
+/*
+ * strncpy_from_user: - Copy a NUL terminated string from userspace.
+ * @dst: Destination address, in kernel space. This buffer must be at
+ * least @count bytes long.
+ * @src: Source address, in user space.
+ * @count: Maximum number of bytes to copy, including the trailing NUL.
+ *
+ * Copies a NUL-terminated string from userspace to kernel space.
+ *
+ * On success, returns the length of the string (not including the trailing
+ * NUL).
+ *
+ * If access to userspace fails, returns -EFAULT (some data may have been
+ * copied).
+ *
+ * If @count is smaller than the length of the string, copies @count bytes
+ * and returns @count.
+ */
+long
+strncpy_from_user(
+ char *dst,
+ const char *src,
+ long count)
+{
+ long res = -EFAULT;
+ if (access_ok(VERIFY_READ, src, 1))
+ __do_strncpy_from_user(dst, src, count, res);
+ return res;
+}
+EXPORT_SYMBOL(strncpy_from_user);
+
+/*
+ * strlen_user: - Get the size of a string in user space.
+ * @str: The string to measure.
+ * @n: The maximum valid length
+ *
+ * Get the size of a NUL-terminated string in user space.
+ *
+ * Returns the size of the string INCLUDING the terminating NUL.
+ * On exception, returns 0.
+ * If the string is too long, returns a value greater than @n.
+ */
+long strnlen_user(const char *s, long n)
+{
+
+ unsigned long res,tmp;
+ if(s){
+ asm volatile(
+ " cmpnei %1, 0 \n"
+ " bf 3f \n"
+ "1: cmpnei %0, 0 \n"
+ " bf 3f \n"
+ "2: ldb %3, (%1, 0) \n"
+ " cmpnei %3, 0 \n"
+ " bf 3f \n"
+ " subi %0, 1 \n"
+ " addi %1, 1 \n"
+ " br 1b \n"
+ "3: subu %2, %0 \n"
+ " addi %2, 1 \n"
+ " br 5f \n"
+ "4: movi %0, 0 \n"
+ " br 5f \n"
+ ".section __ex_table, \"a\" \n"
+ ".align 2 \n"
+ ".long 2b, 4b \n"
+ ".previous \n"
+ "5: \n"
+ :"=r"(n),"=r"(s), "=r"(res), "=r"(tmp)
+ : "0"(n), "1"(s), "2"(n)
+ : "memory", "cc" );
+ return res;
+ }
+ return 0;
+}
+EXPORT_SYMBOL(strnlen_user);
+
+#define __do_clear_user(addr, size) \
+do { \
+ int __d0; \
+ int zvalue; \
+ int tmp; \
+ asm volatile( \
+ "0: cmpnei %1, 0 \n" \
+ " bf 7f \n" \
+ " mov %3, %1 \n" \
+ " andi %3, 3 \n" \
+ " cmpnei %3, 0 \n" \
+ " bf 1f \n" \
+ " br 5f \n" \
+ "1: cmplti %0, 32 \n" /* 4W */ \
+ " bt 3f \n" \
+ "8: stw %2, (%1, 0) \n" \
+ "10: stw %2, (%1, 4) \n" \
+ "11: stw %2, (%1, 8) \n" \
+ "12: stw %2, (%1, 12) \n" \
+ "13: stw %2, (%1, 16) \n" \
+ "14: stw %2, (%1, 20) \n" \
+ "15: stw %2, (%1, 24) \n" \
+ "16: stw %2, (%1, 28) \n" \
+ " addi %1, 32 \n" \
+ " subi %0, 32 \n" \
+ " br 1b \n" \
+ "3: cmplti %0, 4 \n" /* 1W */ \
+ " bt 5f \n" \
+ "4: stw %2, (%1, 0) \n" \
+ " addi %1, 4 \n" \
+ " subi %0, 4 \n" \
+ " br 3b \n" \
+ "5: cmpnei %0, 0 \n" /* 1B */ \
+ "9: bf 7f \n" \
+ "6: stb %2, (%1, 0) \n" \
+ " addi %1, 1 \n" \
+ " subi %0, 1 \n" \
+ " br 5b \n" \
+ ".section __ex_table,\"a\" \n" \
+ ".align 2 \n" \
+ ".long 8b, 9b \n" \
+ ".long 10b, 9b \n" \
+ ".long 11b, 9b \n" \
+ ".long 12b, 9b \n" \
+ ".long 13b, 9b \n" \
+ ".long 14b, 9b \n" \
+ ".long 15b, 9b \n" \
+ ".long 16b, 9b \n" \
+ ".long 4b, 9b \n" \
+ ".long 6b, 9b \n" \
+ ".previous \n" \
+ "7: \n" \
+ : "=r"(size), "=r" (__d0), "=r"(zvalue), "=r"(tmp) \
+ : "0"(size), "1"(addr), "2"(0) \
+ : "memory" \
+ ); \
+} while (0)
+
+/*
+ * clear_user: - Zero a block of memory in user space.
+ * @to: Destination address, in user space.
+ * @n: Number of bytes to zero.
+ *
+ * Zero a block of memory in user space.
+ *
+ * Returns number of bytes that could not be cleared.
+ * On success, this will be zero.
+ */
+unsigned long
+clear_user(void __user *to, unsigned long n)
+{
+ if (access_ok(VERIFY_WRITE, to, n))
+ __do_clear_user(to, n);
+ return n;
+}
+EXPORT_SYMBOL(clear_user);
+
+/*
+ * __clear_user: - Zero a block of memory in user space, with less checking.
+ * @to: Destination address, in user space.
+ * @n: Number of bytes to zero.
+ *
+ * Zero a block of memory in user space. Caller must check
+ * the specified block with access_ok() before calling this function.
+ *
+ * Returns number of bytes that could not be cleared.
+ * On success, this will be zero.
+ */
+unsigned long
+__clear_user(void __user *to, unsigned long n)
+{
+ __do_clear_user(to, n);
+ return n;
+}
+EXPORT_SYMBOL(__clear_user);
--
2.7.4