When doing file migration, QEMU accepts an offset that should be
skipped when writing the migration stream to the file. The purpose of
the offset is to allow the management layer to put its own metadata at
the start of the file.

We have tests for this in migration-test, but only testing that the
migration stream starts at the correct offset and not that it actually
leaves the data intact. Unsurprisingly, there's been a bug in that
area that the tests didn't catch.

Fix the tests to write some data to the offset region and check that
it's actually there after the migration.

While here, switch to using g_get_file_contents() which is more
portable than mmap().

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 tests/qtest/migration-test.c | 79 ++++++++++++++++++++++--------------
 1 file changed, 48 insertions(+), 31 deletions(-)

diff --git a/tests/qtest/migration-test.c b/tests/qtest/migration-test.c
index 0dccb4beff..0a529a527b 100644
--- a/tests/qtest/migration-test.c
+++ b/tests/qtest/migration-test.c
@@ -68,6 +68,7 @@ static QTestMigrationState dst_state;
 #define QEMU_VM_FILE_MAGIC 0x5145564d
 #define FILE_TEST_FILENAME "migfile"
 #define FILE_TEST_OFFSET 0x1000
+#define FILE_TEST_MARKER 'X'
 #define QEMU_ENV_SRC "QTEST_QEMU_BINARY_SRC"
 #define QEMU_ENV_DST "QTEST_QEMU_BINARY_DST"
 
@@ -1693,10 +1694,43 @@ finish:
     test_migrate_end(from, to, args->result == MIG_TEST_SUCCEED);
 }
 
+static void file_dirty_offset_region(void)
+{
+    g_autofree char *path = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
+    size_t size = FILE_TEST_OFFSET;
+    g_autofree char *data = g_new0(char, size);
+
+    memset(data, FILE_TEST_MARKER, size);
+    g_assert(g_file_set_contents(path, data, size, NULL));
+}
+
+static void file_check_offset_region(void)
+{
+    g_autofree char *path = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
+    size_t size = FILE_TEST_OFFSET;
+    g_autofree char *expected = g_new0(char, size);
+    g_autofree char *actual = NULL;
+    uint64_t *stream_start;
+
+    /*
+     * Ensure the skipped offset region's data has not been touched
+     * and the migration stream starts at the right place.
+     */
+
+    memset(expected, FILE_TEST_MARKER, size);
+
+    g_assert(g_file_get_contents(path, &actual, NULL, NULL));
+    g_assert(!memcmp(actual, expected, size));
+
+    stream_start = (uint64_t *)(actual + size);
+    g_assert_cmpint(cpu_to_be64(*stream_start) >> 32, ==, QEMU_VM_FILE_MAGIC);
+}
+
 static void test_file_common(MigrateCommon *args, bool stop_src)
 {
     QTestState *from, *to;
     void *data_hook = NULL;
+    bool check_offset = false;
 
     if (test_migrate_start(&from, &to, args->listen_uri, &args->start)) {
         return;
@@ -1709,6 +1743,16 @@ static void test_file_common(MigrateCommon *args, bool stop_src)
      */
     g_assert_false(args->live);
 
+    if (g_strrstr(args->connect_uri, "offset=")) {
+        check_offset = true;
+        /*
+         * This comes before the start_hook because it's equivalent to
+         * a management application creating the file and writing to
+         * it so hooks should expect the file to be already present.
+         */
+        file_dirty_offset_region();
+    }
+
     if (args->start_hook) {
         data_hook = args->start_hook(from, to);
     }
@@ -1743,6 +1787,10 @@ static void test_file_common(MigrateCommon *args, bool stop_src)
 
     wait_for_serial("dest_serial");
 
+    if (check_offset) {
+        file_check_offset_region();
+    }
+
 finish:
     if (args->finish_hook) {
         args->finish_hook(from, to, data_hook);
@@ -1942,36 +1990,6 @@ static void test_precopy_file(void)
     test_file_common(&args, true);
 }
 
-static void file_offset_finish_hook(QTestState *from, QTestState *to,
-                                    void *opaque)
-{
-#if defined(__linux__)
-    g_autofree char *path = g_strdup_printf("%s/%s", tmpfs, FILE_TEST_FILENAME);
-    size_t size = FILE_TEST_OFFSET + sizeof(QEMU_VM_FILE_MAGIC);
-    uintptr_t *addr, *p;
-    int fd;
-
-    fd = open(path, O_RDONLY);
-    g_assert(fd != -1);
-    addr = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
-    g_assert(addr != MAP_FAILED);
-
-    /*
-     * Ensure the skipped offset contains zeros and the migration
-     * stream starts at the right place.
-     */
-    p = addr;
-    while (p < addr + FILE_TEST_OFFSET / sizeof(uintptr_t)) {
-        g_assert(*p == 0);
-        p++;
-    }
-    g_assert_cmpint(cpu_to_be64(*p) >> 32, ==, QEMU_VM_FILE_MAGIC);
-
-    munmap(addr, size);
-    close(fd);
-#endif
-}
-
 static void test_precopy_file_offset(void)
 {
     g_autofree char *uri = g_strdup_printf("file:%s/%s,offset=%d", tmpfs,
@@ -1980,7 +1998,6 @@ static void test_precopy_file_offset(void)
     MigrateCommon args = {
         .connect_uri = uri,
         .listen_uri = "defer",
-        .finish_hook = file_offset_finish_hook,
     };
 
     test_file_common(&args, false);
-- 
2.35.3