Input: add compat support for sysfs and /proc capabilities output

Input core displays capabilities bitmasks in form of one or more longs printed
in hex form and separated by spaces. Unfortunately it does not work well
for 32-bit applications running on 64-bit kernels since applications expect
that number is "worth" only 32 bits when kernel advances by 64 bits.

Fix that by ensuring that output produced for compat tasks uses 32-bit units.

Reported-and-tested-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/input/input.c

@@ -24,6 +24,7 @@
 #include <linux/mutex.h>
 #include <linux/rcupdate.h>
 #include <linux/smp_lock.h>
+#include "input-compat.h"
 
 MODULE_AUTHOR("Vojtech Pavlik <vojtech@suse.cz>");
 MODULE_DESCRIPTION("Input core");
@@ -764,6 +765,40 @@ static int input_attach_handler(struct input_dev *dev, struct input_handler *han
 	return error;
 }
 
+#ifdef CONFIG_COMPAT
+
+static int input_bits_to_string(char *buf, int buf_size,
+				unsigned long bits, bool skip_empty)
+{
+	int len = 0;
+
+	if (INPUT_COMPAT_TEST) {
+		u32 dword = bits >> 32;
+		if (dword || !skip_empty)
+			len += snprintf(buf, buf_size, "%x ", dword);
+
+		dword = bits & 0xffffffffUL;
+		if (dword || !skip_empty || len)
+			len += snprintf(buf + len, max(buf_size - len, 0),
+					"%x", dword);
+	} else {
+		if (bits || !skip_empty)
+			len += snprintf(buf, buf_size, "%lx", bits);
+	}
+
+	return len;
+}
+
+#else /* !CONFIG_COMPAT */
+
+static int input_bits_to_string(char *buf, int buf_size,
+				unsigned long bits, bool skip_empty)
+{
+	return bits || !skip_empty ?
+		snprintf(buf, buf_size, "%lx", bits) : 0;
+}
+
+#endif
 
 #ifdef CONFIG_PROC_FS
 
@@ -832,14 +867,25 @@ static void input_seq_print_bitmap(struct seq_file *seq, const char *name,
 				   unsigned long *bitmap, int max)
 {
 	int i;
-
-	for (i = BITS_TO_LONGS(max) - 1; i > 0; i--)
-		if (bitmap[i])
-			break;
+	bool skip_empty = true;
+	char buf[18];
 
 	seq_printf(seq, "B: %s=", name);
-	for (; i >= 0; i--)
-		seq_printf(seq, "%lx%s", bitmap[i], i > 0 ? " " : "");
+
+	for (i = BITS_TO_LONGS(max) - 1; i >= 0; i--) {
+		if (input_bits_to_string(buf, sizeof(buf),
+					 bitmap[i], skip_empty)) {
+			skip_empty = false;
+			seq_printf(seq, "%s%s", buf, i > 0 ? " " : "");
+		}
+	}
+
+	/*
+	 * If no output was produced print a single 0.
+	 */
+	if (skip_empty)
+		seq_puts(seq, "0");
+
 	seq_putc(seq, '\n');
 }
 
@@ -1128,14 +1174,23 @@ static int input_print_bitmap(char *buf, int buf_size, unsigned long *bitmap,
 {
 	int i;
 	int len = 0;
+	bool skip_empty = true;
+
+	for (i = BITS_TO_LONGS(max) - 1; i >= 0; i--) {
+		len += input_bits_to_string(buf + len, max(buf_size - len, 0),
+					    bitmap[i], skip_empty);
+		if (len) {
+			skip_empty = false;
+			if (i > 0)
+				len += snprintf(buf + len, max(buf_size - len, 0), " ");
+		}
+	}
 
-	for (i = BITS_TO_LONGS(max) - 1; i > 0; i--)
-		if (bitmap[i])
-			break;
-
-	for (; i >= 0; i--)
-		len += snprintf(buf + len, max(buf_size - len, 0),
-				"%lx%s", bitmap[i], i > 0 ? " " : "");
+	/*
+	 * If no output was produced print a single 0.
+	 */
+	if (len == 0)
+		len = snprintf(buf, buf_size, "%d", 0);
 
 	if (add_cr)
 		len += snprintf(buf + len, max(buf_size - len, 0), "\n");
@@ -1150,7 +1205,8 @@ static ssize_t input_dev_show_cap_##bm(struct device *dev,		\
 {									\
 	struct input_dev *input_dev = to_input_dev(dev);		\
 	int len = input_print_bitmap(buf, PAGE_SIZE,			\
-				     input_dev->bm##bit, ev##_MAX, 1);	\
+				     input_dev->bm##bit, ev##_MAX,	\
+				     true);				\
 	return min_t(int, len, PAGE_SIZE);				\
 }									\
 static DEVICE_ATTR(bm, S_IRUGO, input_dev_show_cap_##bm, NULL)
@@ -1214,7 +1270,7 @@ static int input_add_uevent_bm_var(struct kobj_uevent_env *env,
 
 	len = input_print_bitmap(&env->buf[env->buflen - 1],
 				 sizeof(env->buf) - env->buflen,
-				 bitmap, max, 0);
+				 bitmap, max, false);
 	if (len >= (sizeof(env->buf) - env->buflen))
 		return -ENOMEM;