string: Add strlcat helper

We will need it for btrfs subvolumes handling.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

Makefile.config

@@ -15,6 +15,9 @@ ifeq ($(call try-cc,$(PRLIMIT_TEST),,),y)
 endif
 ifeq ($(call try-cc,$(STRLCPY_TEST),,),y)
 	$(Q) @echo '#define CONFIG_HAS_STRLCPY' >> $@
+endif
+ifeq ($(call try-cc,$(STRLCAT_TEST),,),y)
+	$(Q) @echo '#define CONFIG_HAS_STRLCAT' >> $@
 endif
 	$(Q) @echo '#endif /* __CR_CONFIG_H__ */' >> $@
 

include/string.h

@@ -10,4 +10,8 @@
 extern size_t strlcpy(char *dest, const char *src, size_t size);
 #endif
 
+#ifndef CONFIG_HAS_STRLCAT
+extern size_t strlcat(char *dest, const char *src, size_t count);
+#endif
+
 #endif /* __CR_STRING_H__ */

scripts/feature-tests.mak

@@ -42,3 +42,16 @@ int main(void)
 	return strlcpy(dst, src, sizeof(dst));
 }
 endef
+
+define STRLCAT_TEST
+
+#include <string.h>
+
+int main(void)
+{
+	char src[32] = "strlcat";
+	char dst[32];
+
+	return strlcat(dst, src, sizeof(dst));
+}
+endef

string.c

@@ -30,3 +30,31 @@ size_t strlcpy(char *dest, const char *src, size_t size)
 	return ret;
 }
 #endif
+
+#ifndef CONFIG_HAS_STRLCAT
+/**
+ * strlcat - Append a length-limited, %NUL-terminated string to another
+ * @dest: The string to be appended to
+ * @src: The string to append to it
+ * @count: The size of the destination buffer.
+ */
+size_t strlcat(char *dest, const char *src, size_t count)
+{
+	size_t dsize = strlen(dest);
+	size_t len = strlen(src);
+	size_t res = dsize + len;
+
+	/*
+	 * It's assumed that @dsize strictly
+	 * less than count. Otherwise it's
+	 * a bug. But we left it to a caller.
+	 */
+	dest += dsize;
+	count -= dsize;
+	if (len >= count)
+		len = count-1;
+	memcpy(dest, src, len);
+	dest[len] = 0;
+	return res;
+}
+#endif