Hexagon: Add user access functions

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+/*
+ * User memory access support for Hexagon
+ *
+ * Copyright (c) 2010-2011, Code Aurora Forum. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+#ifndef _ASM_UACCESS_H
+#define _ASM_UACCESS_H
+/*
+ * User space memory access functions
+ */
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <asm/segment.h>
+#include <asm/sections.h>
+
+/*
+ * access_ok: - Checks if a user space pointer is valid
+ * @type: Type of access: %VERIFY_READ or %VERIFY_WRITE.  Note that
+ *        %VERIFY_WRITE is a superset of %VERIFY_READ - if it is safe
+ *        to write to a block, it is always safe to read from it.
+ * @addr: User space pointer to start of block to check
+ * @size: Size of block to check
+ *
+ * Context: User context only.  This function may sleep.
+ *
+ * Checks if a pointer to a block of memory in user space is valid.
+ *
+ * Returns true (nonzero) if the memory block *may* be valid, false (zero)
+ * if it is definitely invalid.
+ *
+ * User address space in Hexagon, like x86, goes to 0xbfffffff, so the
+ * simple MSB-based tests used by MIPS won't work.  Some further
+ * optimization is probably possible here, but for now, keep it
+ * reasonably simple and not *too* slow.  After all, we've got the
+ * MMU for backup.
+ */
+#define VERIFY_READ     0
+#define VERIFY_WRITE    1
+
+#define __access_ok(addr, size) \
+	((get_fs().seg == KERNEL_DS.seg) || \
+	(((unsigned long)addr < get_fs().seg) && \
+	  (unsigned long)size < (get_fs().seg - (unsigned long)addr)))
+
+/*
+ * When a kernel-mode page fault is taken, the faulting instruction
+ * address is checked against a table of exception_table_entries.
+ * Each entry is a tuple of the address of an instruction that may
+ * be authorized to fault, and the address at which execution should
+ * be resumed instead of the faulting instruction, so as to effect
+ * a workaround.
+ */
+
+/*  Assembly somewhat optimized copy routines  */
+unsigned long __copy_from_user_hexagon(void *to, const void __user *from,
+				     unsigned long n);
+unsigned long __copy_to_user_hexagon(void __user *to, const void *from,
+				   unsigned long n);
+
+#define __copy_from_user(to, from, n) __copy_from_user_hexagon(to, from, n)
+#define __copy_to_user(to, from, n) __copy_to_user_hexagon(to, from, n)
+
+/*
+ * XXX todo: some additonal performance gain is possible by
+ * implementing __copy_to/from_user_inatomic, which is much
+ * like __copy_to/from_user, but performs slightly less checking.
+ */
+
+__kernel_size_t __clear_user_hexagon(void __user *dest, unsigned long count);
+#define __clear_user(a, s) __clear_user_hexagon((a), (s))
+
+#define __strncpy_from_user(dst, src, n) hexagon_strncpy_from_user(dst, src, n)
+
+/*  get around the ifndef in asm-generic/uaccess.h  */
+#define __strnlen_user __strnlen_user
+
+extern long __strnlen_user(const char __user *src, long n);
+
+static inline long hexagon_strncpy_from_user(char *dst, const char __user *src,
+					     long n);
+
+#include <asm-generic/uaccess.h>
+
+/*  Todo:  an actual accelerated version of this.  */
+static inline long hexagon_strncpy_from_user(char *dst, const char __user *src,
+					     long n)
+{
+	long res = __strnlen_user(src, n);
+
+	/* return from strnlen can't be zero -- that would be rubbish. */
+
+	if (res > n) {
+		copy_from_user(dst, src, n);
+		return n;
+	} else {
+		copy_from_user(dst, src, res);
+		return res-1;
+	}
+}
+
+#endif

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