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>

5 files changed, 162 insertions, 0 deletions

diff --git a/include/linux/string.h b/include/linux/string.h
index 4a5a0eb7df51..27d0482e5e05 100644
--- a/include/linux/string.h
+++ b/include/linux/string.h
@@ -131,6 +131,13 @@ static inline void *memset_p(void **p, void *v, __kernel_size_t n)
                 return memset64((uint64_t *)p, (uintptr_t)v, n);
 }
 
+extern void **__memcat_p(void **a, void **b);
+#define memcat_p(a, b) ({                                       \
+        BUILD_BUG_ON_MSG(!__same_type(*(a), *(b)),              \
+                         "type mismatch in memcat_p()");        \
+        (typeof(*a) *)__memcat_p((void **)(a), (void **)(b));   \
+})
+
 #ifndef __HAVE_ARCH_MEMCPY
 extern void * memcpy(void *,const void *,__kernel_size_t);
 #endif
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4966c4fbe7f7..c0176510262e 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1965,6 +1965,14 @@ config TEST_DEBUG_VIRTUAL
 
           If unsure, say N.
 
+config TEST_MEMCAT_P
+        tristate "Test memcat_p() helper function"
+        help
+          Test the memcat_p() helper for correctly merging two
+          pointer arrays together.
+
+          If unsure, say N.
+
 endif # RUNTIME_TESTING_MENU
 
 config MEMTEST
diff --git a/lib/Makefile b/lib/Makefile
index ca3f7ebb900d..c2588a2d7b1e 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -71,6 +71,7 @@ obj-$(CONFIG_TEST_UUID) += test_uuid.o
 obj-$(CONFIG_TEST_PARMAN) += test_parman.o
 obj-$(CONFIG_TEST_KMOD) += test_kmod.o
 obj-$(CONFIG_TEST_DEBUG_VIRTUAL) += test_debug_virtual.o
+obj-$(CONFIG_TEST_MEMCAT_P) += test_memcat_p.o
 
 ifeq ($(CONFIG_DEBUG_KOBJECT),y)
 CFLAGS_kobject.o += -DDEBUG
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
diff --git a/lib/test_memcat_p.c b/lib/test_memcat_p.c
new file mode 100644
index 000000000000..2b163a749ecb
--- /dev/null
+++ b/lib/test_memcat_p.c
@@ -0,0 +1,115 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Test cases for memcat_p() in lib/string.c
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+
+struct test_struct {
+        int             num;
+        unsigned int    magic;
+};
+
+#define MAGIC           0xf00ff00f
+/* Size of each of the NULL-terminated input arrays */
+#define INPUT_MAX       128
+/* Expected number of non-NULL elements in the output array */
+#define EXPECT          (INPUT_MAX * 2 - 2)
+
+static int __init test_memcat_p_init(void)
+{
+        struct test_struct **in0, **in1, **out, **p;
+        int err = -ENOMEM, i, r, total = 0;
+
+        in0 = kcalloc(INPUT_MAX, sizeof(*in0), GFP_KERNEL);
+        if (!in0)
+                return err;
+
+        in1 = kcalloc(INPUT_MAX, sizeof(*in1), GFP_KERNEL);
+        if (!in1)
+                goto err_free_in0;
+
+        for (i = 0, r = 1; i < INPUT_MAX - 1; i++) {
+                in0[i] = kmalloc(sizeof(**in0), GFP_KERNEL);
+                if (!in0[i])
+                        goto err_free_elements;
+
+                in1[i] = kmalloc(sizeof(**in1), GFP_KERNEL);
+                if (!in1[i]) {
+                        kfree(in0[i]);
+                        goto err_free_elements;
+                }
+
+                /* lifted from test_sort.c */
+                r = (r * 725861) % 6599;
+                in0[i]->num = r;
+                in1[i]->num = -r;
+                in0[i]->magic = MAGIC;
+                in1[i]->magic = MAGIC;
+        }
+
+        in0[i] = in1[i] = NULL;
+
+        out = memcat_p(in0, in1);
+        if (!out)
+                goto err_free_all_elements;
+
+        err = -EINVAL;
+        for (i = 0, p = out; *p && (i < INPUT_MAX * 2 - 1); p++, i++) {
+                total += (*p)->num;
+
+                if ((*p)->magic != MAGIC) {
+                        pr_err("test failed: wrong magic at %d: %u\n", i,
+                               (*p)->magic);
+                        goto err_free_out;
+                }
+        }
+
+        if (total) {
+                pr_err("test failed: expected zero total, got %d\n", total);
+                goto err_free_out;
+        }
+
+        if (i != EXPECT) {
+                pr_err("test failed: expected output size %d, got %d\n",
+                       EXPECT, i);
+                goto err_free_out;
+        }
+
+        for (i = 0; i < INPUT_MAX - 1; i++)
+                if (out[i] != in0[i] || out[i + INPUT_MAX - 1] != in1[i]) {
+                        pr_err("test failed: wrong element order at %d\n", i);
+                        goto err_free_out;
+                }
+
+        err = 0;
+        pr_info("test passed\n");
+
+err_free_out:
+        kfree(out);
+err_free_all_elements:
+        i = INPUT_MAX;
+err_free_elements:
+        for (i--; i >= 0; i--) {
+                kfree(in1[i]);
+                kfree(in0[i]);
+        }
+
+        kfree(in1);
+err_free_in0:
+        kfree(in0);
+
+        return err;
+}
+
+static void __exit test_memcat_p_exit(void)
+{
+}
+
+module_init(test_memcat_p_init);
+module_exit(test_memcat_p_exit);
+
+MODULE_LICENSE("GPL");