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    Subject[GIT PULL 15/16] lib: Add memcat_p(): paste 2 pointer arrays together
    Date
    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>
    ---
    include/linux/string.h | 7 +++
    lib/Kconfig.debug | 8 +++
    lib/Makefile | 1 +
    lib/string.c | 31 +++++++++++
    lib/test_memcat_p.c | 115 +++++++++++++++++++++++++++++++++++++++++
    5 files changed, 162 insertions(+)
    create mode 100644 lib/test_memcat_p.c

    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 613316724c6a..177e21006359 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");
    --
    2.19.0
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