[PATCH 1/4] uaccess: add copy_word_from_user

[Steven Rostedt]

From: Steven Rostedt <srostedt@xxxxxxxxxx>

The ftrace utility reads space delimited words from user space.
Andrew Morton did not like how ftrace open coded this. He had
a good point since more than one location performed this feature.

This patch creates a copy_word_from_user function that can copy
a space delimited word from user space. This puts the code in
a new lib/uaccess.c file. This keeps the code in a single location
and may be optimized in the future.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
---
 include/linux/uaccess.h |    4 ++
 lib/Makefile            |    3 +-
 lib/uaccess.c           |  134 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 140 insertions(+), 1 deletions(-)
 create mode 100644 lib/uaccess.c

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 6b58367..2d706d9 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -106,4 +106,8 @@ extern long probe_kernel_read(void *dst, void *src, size_t size);
  */
 extern long probe_kernel_write(void *dst, void *src, size_t size);
 
+extern int copy_word_from_user(void *to, const void __user *from,
+			       unsigned int copy, unsigned int read,
+			       unsigned int *copied, int skip);
+
 #endif		/* __LINUX_UACCESS_H__ */
diff --git a/lib/Makefile b/lib/Makefile
index 32b0e64..46ce28c 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -11,7 +11,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 rbtree.o radix-tree.o dump_stack.o \
 	 idr.o int_sqrt.o extable.o prio_tree.o \
 	 sha1.o irq_regs.o reciprocal_div.o argv_split.o \
-	 proportions.o prio_heap.o ratelimit.o show_mem.o is_single_threaded.o
+	 proportions.o prio_heap.o ratelimit.o show_mem.o is_single_threaded.o \
+	 uaccess.o
 
 lib-$(CONFIG_MMU) += ioremap.o
 lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/uaccess.c b/lib/uaccess.c
new file mode 100644
index 0000000..5b9a4ac
--- /dev/null
+++ b/lib/uaccess.c
@@ -0,0 +1,134 @@
+/*
+ * lib/uaccess.c
+ * generic user access file.
+ *
+ * started by Steven Rostedt
+ *
+ *  Copyright (C) 2009 Red Hat, Inc., Steven Rostedt <srostedt@xxxxxxxxxx>
+ *
+ * This source code is licensed under the GNU General Public License,
+ * Version 2.  See the file COPYING for more details.
+ */
+#include <linux/uaccess.h>
+#include <linux/ctype.h>
+
+/**
+ * copy_word_from_user - copy a space delimited word from user space
+ * @to:	     The location to copy to
+ * @from:    The location to copy from
+ * @copy:    The number of bytes to copy
+ * @read:    The number of bytes to read
+ * @copied:  The number of bytes actually copied to @to
+ * @skip:    If other than zero, will skip leading white space
+ *
+ * This reads from a user buffer, a space delimited word.
+ * If skip is set, then it will trim all leading white space.
+ * Then it will copy all non white space until @copy bytes have
+ * been copied, @read bytes have been read from the user buffer,
+ * or more white space has been encountered.
+ *
+ * Note, if skip is not set, and white space exists at the beginning
+ *  it will return immediately.
+ *
+ * Returns:
+ *  The number of bytes read from user space
+ *
+ *  -EAGAIN, if we copied a word successfully, but never hit
+ *    ending white space. The number of bytes copied will be the same
+ *    as @read. Note, if skip is set, and all we hit was white space
+ *    then we will also returne -EAGAIN with @copied = 0.
+ *
+ *  @copied will contain the number of bytes copied into @to
+ *
+ *  -EFAULT, if we faulted during any part of the copy.
+ *     @copied will be undefined.
+ *
+ *  -EINVAL, if we fill up @from before hitting white space.
+ *    @copy must be bigger than the expected word to read.
+ */
+int copy_word_from_user(void *to, const void __user *from,
+			unsigned int copy, unsigned int read,
+			unsigned int *copied, int skip)
+{
+	unsigned int have_read = 0;
+	unsigned int have_copied = 0;
+	const char __user *user = from;
+	char *kern = to;
+	int ret;
+	char ch;
+
+	/* get the first character */
+	ret = get_user(ch, user++);
+	if (ret)
+		return ret;
+	have_read++;
+
+	/*
+	 * If skip is set, and the first character is white space
+	 * then we will continue to read until we find non white space.
+	 */
+	if (skip) {
+		while (have_read < read && isspace(ch)) {
+			ret = get_user(ch, user++);
+			if (ret)
+				return ret;
+			have_read++;
+		}
+
+		/*
+		 * If ch is still white space, then have_read == read.
+		 * We successfully copied zero bytes. But this is
+		 * still valid. Just let the caller try again.
+		 */
+		if (isspace(ch)) {
+			ret = -EAGAIN;
+			goto out;
+		}
+	} else if (isspace(ch)) {
+		/*
+		 * If skip was not set and the first character was
+		 * white space, then we return immediately.
+		 */
+		ret = have_read;
+		goto out;
+	}
+
+
+	/* Now read the actual word */
+	while (have_read < read &&
+	       have_copied < copy && !isspace(ch)) {
+
+		kern[have_copied++] = ch;
+
+		ret = get_user(ch, user++);
+		if (ret)
+			return ret;
+
+		have_read++;
+	}
+
+	/*
+	 * If we ended with white space then we have successfully
+	 * read in a full word.
+	 *
+	 * If ch is not white space, and we have filled up @from,
+	 * then this was an invalid word.
+	 *
+	 * If ch is not white space, and we still have room in @from
+	 * then we let the caller know we have split a word.
+	 *  (have_read == read)
+	 */
+	if (isspace(ch))
+		ret = have_read;
+	else if (have_copied == copy)
+		ret = -EINVAL;
+	else {
+		WARN_ON(have_read != read);
+		ret = -EAGAIN;
+	}
+
+ out:
+	*copied = have_copied;
+
+	return ret;
+}
-- 
1.5.6.5

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