saner calling conventions for csum_and_copy_..._user()

All callers of these primitives will
	* discard anything we might've copied in case of error
	* ignore the csum value in case of error
	* always pass 0xffffffff as the initial sum, so the
resulting csum value (in case of success, that is) will never be 0.

That suggest the following calling conventions:
	* don't pass err_ptr - just return 0 on error.
	* don't bother with zeroing destination, etc. in case of error
	* don't pass the initial sum - just use 0xffffffff.

This commit does the minimal conversion in the instances of csum_and_copy_...();
the changes of actual asm code behind them are done later in the series.
Note that this asm code is often shared with csum_partial_copy_nocheck();
the difference is that csum_partial_copy_nocheck() passes 0 for initial
sum while csum_and_copy_..._user() pass 0xffffffff.  Fortunately, we are
free to pass 0xffffffff in all cases and subsequent patches will use that
freedom without any special comments.

A part that could be split off: parisc and uml/i386 claimed to have
csum_and_copy_to_user() instances of their own, but those were identical
to the generic one, so we simply drop them.  Not sure if it's worth
a separate commit...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 22 insertions, 24 deletions

diff --git a/arch/mips/include/asm/checksum.h b/arch/mips/include/asm/checksum.h
index ec3159dbc1b3..9dfce3522760 100644
--- a/arch/mips/include/asm/checksum.h
+++ b/arch/mips/include/asm/checksum.h
@@ -60,16 +60,15 @@ __wsum csum_partial_copy_from_user(const void __user *src, void *dst, int len,
 
 #define _HAVE_ARCH_COPY_AND_CSUM_FROM_USER
 static inline
-__wsum csum_and_copy_from_user(const void __user *src, void *dst,
-			       int len, __wsum sum, int *err_ptr)
+__wsum csum_and_copy_from_user(const void __user *src, void *dst, int len)
 {
-	if (access_ok(src, len))
-		return csum_partial_copy_from_user(src, dst, len, sum,
-						   err_ptr);
-	if (len)
-		*err_ptr = -EFAULT;
+	__wsum sum = ~0U;
+	int err = 0;
 
-	return sum;
+	if (!access_ok(src, len))
+		return 0;
+	sum = csum_partial_copy_from_user(src, dst, len, sum, &err);
+	return err ? 0 : sum;
 }
 
 /*
@@ -77,24 +76,23 @@ __wsum csum_and_copy_from_user(const void __user *src, void *dst,
  */
 #define HAVE_CSUM_COPY_USER
 static inline
-__wsum csum_and_copy_to_user(const void *src, void __user *dst, int len,
-			     __wsum sum, int *err_ptr)
+__wsum csum_and_copy_to_user(const void *src, void __user *dst, int len)
 {
+	int err = 0;
+	__wsum sum = ~0U;
+
 	might_fault();
-	if (access_ok(dst, len)) {
-		if (uaccess_kernel())
-			return __csum_partial_copy_kernel(src,
-							  (__force void *)dst,
-							  len, sum, err_ptr);
-		else
-			return __csum_partial_copy_to_user(src,
-							   (__force void *)dst,
-							   len, sum, err_ptr);
-	}
-	if (len)
-		*err_ptr = -EFAULT;
-
-	return (__force __wsum)-1; /* invalid checksum */
+	if (!access_ok(dst, len))
+		return 0;
+	if (uaccess_kernel())
+		sum = __csum_partial_copy_kernel(src,
+						  (__force void *)dst,
+						  len, sum, &err);
+	else
+		sum = __csum_partial_copy_to_user(src,
+						   (__force void *)dst,
+						   len, sum, &err);
+	return err ? 0 : sum;
 }
 
 /*