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    Subject[PATCH 5/9] userfaultfd/selftests: use memfd_create for shmem test type
    From
    This is a preparatory commit. In the future, we want to be able to setup
    alias mappings for area_src and area_dst in the shmem test, like we do
    in the hugetlb_shared test. With a VMA obtained via
    mmap(MAP_ANONYMOUS | MAP_SHARED), it isn't clear how to do this.

    So, mmap() with an fd, so we can create alias mappings. Use memfd_create
    instead of actually passing in a tmpfs path like hugetlb does, since
    it's more convenient / simpler to run, and works just as well.

    Future commits will:

    1. Setup the alias mappings.
    2. Extend our tests to actually take advantage of this, to test new
    userfaultfd behavior being introduced in this series.

    Also, a small fix in the area we're changing: when the hugetlb setup
    fails in main(), pass in the right argv[] so we actually print out the
    hugetlb file path.

    Signed-off-by: Axel Rasmussen <axelrasmussen@google.com>
    ---
    tools/testing/selftests/vm/userfaultfd.c | 18 ++++++++++++++++--
    1 file changed, 16 insertions(+), 2 deletions(-)

    diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c
    index 310fc617c383..b0af88b258d7 100644
    --- a/tools/testing/selftests/vm/userfaultfd.c
    +++ b/tools/testing/selftests/vm/userfaultfd.c
    @@ -85,6 +85,7 @@ static bool test_uffdio_wp = false;
    static bool test_uffdio_minor = false;

    static bool map_shared;
    +static int shm_fd;
    static int huge_fd;
    static char *huge_fd_off0;
    static unsigned long long *count_verify;
    @@ -278,10 +279,13 @@ static void shmem_release_pages(char *rel_area)

    static void shmem_allocate_area(void **alloc_area)
    {
    + unsigned long offset =
    + alloc_area == (void **)&area_src ? 0 : nr_pages * page_size;
    +
    *alloc_area = mmap(NULL, nr_pages * page_size, PROT_READ | PROT_WRITE,
    - MAP_ANONYMOUS | MAP_SHARED, -1, 0);
    + MAP_SHARED, shm_fd, offset);
    if (*alloc_area == MAP_FAILED)
    - err("shared memory mmap failed");
    + err("mmap of memfd failed");
    }

    struct uffd_test_ops {
    @@ -1446,6 +1450,16 @@ int main(int argc, char **argv)
    err("Open of %s failed", argv[4]);
    if (ftruncate(huge_fd, 0))
    err("ftruncate %s to size 0 failed", argv[4]);
    + } else if (test_type == TEST_SHMEM) {
    + shm_fd = memfd_create(argv[0], 0);
    + if (shm_fd < 0)
    + err("memfd_create");
    + if (ftruncate(shm_fd, nr_pages * page_size * 2))
    + err("ftruncate");
    + if (fallocate(shm_fd,
    + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, 0,
    + nr_pages * page_size * 2))
    + err("fallocate");
    }
    printf("nr_pages: %lu, nr_pages_per_cpu: %lu\n",
    nr_pages, nr_pages_per_cpu);
    --
    2.31.1.295.g9ea45b61b8-goog
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