Re: [PATCH] tests/qtest/migrate-test: Add a postcopy memfile test

[Fabiano Rosas <farosas@suse.de>]

Nicholas Piggin <npiggin@gmail.com> writes:

> Postcopy requires userfaultfd support, which requires tmpfs if a memory
> file is used.
>
> This adds back support for /dev/shm memory files, but adds preallocation
> to skip environments where that mount is limited in size.
>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>
> How about this? This goes on top of the reset of the patches
> (I'll re-send them all as a series if we can get to some agreement).
>
> This adds back the /dev/shm option with preallocation and adds a test
> case that requires tmpfs.

Peter has stronger opinions on this than I do. I'll leave it to him to
decide.

Just note that now we're making the CI less deterministic in relation to
the migration tests. When a test that uses shmem fails, we'll not be
able to consistently reproduce because the test might not even run
depending on what has consumed the shmem first.

Let's also take care that the other consumers of shmem (I think just
ivshmem-test) are able to cope with the migration-test taking all the
space, otherwise the CI will still break.

>
> Thanks,
> Nick
>
>  tests/qtest/migration-test.c | 63 +++++++++++++++++++++++++++++++-----
>  1 file changed, 55 insertions(+), 8 deletions(-)
>
> diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
> index 86eace354e..7fd9bbdc18 100644
> --- a/tests/qtest/migration-test.c
> +++ b/tests/qtest/migration-test.c
> @@ -11,6 +11,7 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include "qemu/cutils.h"
>  
>  #include "libqtest.h"
>  #include "qapi/qmp/qdict.h"
> @@ -553,6 +554,7 @@ typedef struct {
>       */
>      bool hide_stderr;
>      bool use_memfile;
> +    bool use_uffd_memfile;
>      /* only launch the target process */
>      bool only_target;
>      /* Use dirty ring if true; dirty logging otherwise */
> @@ -739,7 +741,48 @@ static int test_migrate_start(QTestState **from, QTestState **to,
>          ignore_stderr = "";
>      }
>  
> -    if (args->use_memfile) {
> +    if (!qtest_has_machine(machine_alias)) {
> +        g_autofree char *msg = g_strdup_printf("machine %s not supported",
> +                                               machine_alias);
> +        g_test_skip(msg);
> +        return -1;
> +    }
> +
> +    if (args->use_uffd_memfile) {
> +#if defined(__NR_userfaultfd) && defined(__linux__)
> +        int fd;
> +        uint64_t size;
> +
> +        if (!g_file_test("/dev/shm", G_FILE_TEST_IS_DIR)) {
> +            g_test_skip("/dev/shm does not exist or is not a directory");
> +            return -1;
> +        }
> +
> +        /*
> +         * Pre-create and allocate the file here, because /dev/shm/
> +         * is known to be limited in size in some places (e.g., Gitlab CI).
> +         */
> +        memfile_path = g_strdup_printf("/dev/shm/qemu-%d", getpid());
> +        fd = open(memfile_path, O_WRONLY | O_CREAT | O_EXCL, S_IRUSR | S_IWUSR);
> +        if (fd == -1) {
> +            g_test_skip("/dev/shm file could not be created");
> +            return -1;
> +        }
> +
> +        g_assert(qemu_strtosz(memory_size, NULL, &size) == 0);
> +        size += 64*1024; /* QEMU may map a bit more memory for a guard page */
> +
> +        if (fallocate(fd, 0, 0, size) == -1) {
> +            unlink(memfile_path);
> +            perror("could not alloc"); exit(1);
> +            g_test_skip("Could not allocate machine memory in /dev/shm");
> +            return -1;
> +        }
> +        close(fd);
> +#else
> +        g_test_skip("userfaultfd is not supported");
> +#endif
> +    } else if (args->use_memfile) {
>          memfile_path = g_strdup_printf("/%s/qemu-%d", tmpfs, getpid());
>          memfile_opts = g_strdup_printf(
>              "-object memory-backend-file,id=mem0,size=%s"
> @@ -751,12 +794,6 @@ static int test_migrate_start(QTestState **from, QTestState **to,
>          kvm_opts = ",dirty-ring-size=4096";
>      }
>  
> -    if (!qtest_has_machine(machine_alias)) {
> -        g_autofree char *msg = g_strdup_printf("machine %s not supported", machine_alias);
> -        g_test_skip(msg);
> -        return -1;
> -    }
> -
>      machine = resolve_machine_version(machine_alias, QEMU_ENV_SRC,
>                                        QEMU_ENV_DST);
>  
> @@ -807,7 +844,7 @@ static int test_migrate_start(QTestState **from, QTestState **to,
>       * Remove shmem file immediately to avoid memory leak in test failed case.
>       * It's valid because QEMU has already opened this file
>       */
> -    if (args->use_memfile) {
> +    if (args->use_memfile || args->use_uffd_memfile) {
>          unlink(memfile_path);
>      }
>  
> @@ -1275,6 +1312,15 @@ static void test_postcopy(void)
>      test_postcopy_common(&args);
>  }
>  
> +static void test_postcopy_memfile(void)
> +{
> +    MigrateCommon args = {
> +        .start.use_uffd_memfile = true,
> +    };
> +
> +    test_postcopy_common(&args);
> +}
> +
>  static void test_postcopy_suspend(void)
>  {
>      MigrateCommon args = {
> @@ -3441,6 +3487,7 @@ int main(int argc, char **argv)
>  
>      if (has_uffd) {
>          migration_test_add("/migration/postcopy/plain", test_postcopy);
> +        migration_test_add("/migration/postcopy/memfile", test_postcopy_memfile);
>          migration_test_add("/migration/postcopy/recovery/plain",
>                             test_postcopy_recovery);
>          migration_test_add("/migration/postcopy/preempt/plain",