lib: Add memcat_p(): paste 2 pointer arrays together

This adds a helper to paste 2 pointer arrays together, useful for merging
various types of attribute arrays. There are a few places in the kernel
tree where this is open coded, and I just added one more in the STM class.

The naming is inspired by memset_p() and memcat(), and partial credit for
it goes to Andy Shevchenko.

This patch adds the function wrapped in a type-enforcing macro and a test
module.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 31 insertions, 0 deletions

diff --git a/lib/string.c b/lib/string.c
index 2c0900a5d51a..453f35994eb6 100644
--- a/lib/string.c
+++ b/lib/string.c
@@ -27,6 +27,7 @@
 #include <linux/export.h>
 #include <linux/bug.h>
 #include <linux/errno.h>
+#include <linux/slab.h>
 
 #include <asm/byteorder.h>
 #include <asm/word-at-a-time.h>
@@ -890,6 +891,36 @@ void *memscan(void *addr, int c, size_t size)
 EXPORT_SYMBOL(memscan);
 #endif
 
+/*
+ * Merge two NULL-terminated pointer arrays into a newly allocated
+ * array, which is also NULL-terminated. Nomenclature is inspired by
+ * memset_p() and memcat() found elsewhere in the kernel source tree.
+ */
+void **__memcat_p(void **a, void **b)
+{
+	void **p = a, **new;
+	int nr;
+
+	/* count the elements in both arrays */
+	for (nr = 0, p = a; *p; nr++, p++)
+		;
+	for (p = b; *p; nr++, p++)
+		;
+	/* one for the NULL-terminator */
+	nr++;
+
+	new = kmalloc_array(nr, sizeof(void *), GFP_KERNEL);
+	if (!new)
+		return NULL;
+
+	/* nr -> last index; p points to NULL in b[] */
+	for (nr--; nr >= 0; nr--, p = p == b ? &a[nr] : p - 1)
+		new[nr] = *p;
+
+	return new;
+}
+EXPORT_SYMBOL_GPL(__memcat_p);
+
 #ifndef __HAVE_ARCH_STRSTR
 /**
  * strstr - Find the first substring in a %NUL terminated string