[PULL,03/58] block: Refactor get_tmp_filename()

diff --git a/include/block/block_int-common.h b/include/block/block_int-common.h
index 8947abab76..d7c0a7e96f 100644
--- a/include/block/block_int-common.h
+++ b/include/block/block_int-common.h
@@ -1230,7 +1230,7 @@  static inline BlockDriverState *child_bs(BdrvChild *child)
 }
 
 int bdrv_check_request(int64_t offset, int64_t bytes, Error **errp);
-int get_tmp_filename(char *filename, int size);
+char *create_tmp_file(Error **errp);
 void bdrv_parse_filename_strip_prefix(const char *filename, const char *prefix,
                                       QDict *options);
 
diff --git a/block.c b/block.c
index 66a35b3982..c8374dac4f 100644
--- a/block.c
+++ b/block.c
@@ -861,35 +861,42 @@  int bdrv_probe_geometry(BlockDriverState *bs, HDGeometry *geo)
 
 /*
  * Create a uniquely-named empty temporary file.
- * Return 0 upon success, otherwise a negative errno value.
+ * Return the actual file name used upon success, otherwise NULL.
+ * This string should be freed with g_free() when not needed any longer.
+ *
+ * Note: creating a temporary file for the caller to (re)open is
+ * inherently racy. Use g_file_open_tmp() instead whenever practical.
  */
-int get_tmp_filename(char *filename, int size)
+char *create_tmp_file(Error **errp)
 {
-#ifdef _WIN32
-    char temp_dir[MAX_PATH];
-    /* GetTempFileName requires that its output buffer (4th param)
-       have length MAX_PATH or greater.  */
-    assert(size >= MAX_PATH);
-    return (GetTempPath(MAX_PATH, temp_dir)
-            && GetTempFileName(temp_dir, "qem", 0, filename)
-            ? 0 : -GetLastError());
-#else
     int fd;
     const char *tmpdir;
-    tmpdir = getenv("TMPDIR");
-    if (!tmpdir) {
+    g_autofree char *filename = NULL;
+
+    tmpdir = g_get_tmp_dir();
+#ifndef _WIN32
+    /*
+     * See commit 69bef79 ("block: use /var/tmp instead of /tmp for -snapshot")
+     *
+     * This function is used to create temporary disk images (like -snapshot),
+     * so the files can become very large. /tmp is often a tmpfs where as
+     * /var/tmp is usually on a disk, so more appropriate for disk images.
+     */
+    if (!g_strcmp0(tmpdir, "/tmp")) {
         tmpdir = "/var/tmp";
     }
-    if (snprintf(filename, size, "%s/vl.XXXXXX", tmpdir) >= size) {
-        return -EOVERFLOW;
-    }
-    fd = mkstemp(filename);
+#endif
+
+    filename = g_strdup_printf("%s/vl.XXXXXX", tmpdir);
+    fd = g_mkstemp(filename);
     if (fd < 0) {
-        return -errno;
+        error_setg_errno(errp, errno, "Could not open temporary file '%s'",
+                         filename);
+        return NULL;
     }
     close(fd);
-    return 0;
-#endif
+
+    return g_steal_pointer(&filename);
 }
 
 /*
@@ -3715,8 +3722,7 @@  static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
                                                    QDict *snapshot_options,
                                                    Error **errp)
 {
-    /* TODO: extra byte is a hack to ensure MAX_PATH space on Windows. */
-    char *tmp_filename = g_malloc0(PATH_MAX + 1);
+    g_autofree char *tmp_filename = NULL;
     int64_t total_size;
     QemuOpts *opts = NULL;
     BlockDriverState *bs_snapshot = NULL;
@@ -3735,9 +3741,8 @@  static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
     }
 
     /* Create the temporary image */
-    ret = get_tmp_filename(tmp_filename, PATH_MAX + 1);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "Could not get temporary filename");
+    tmp_filename = create_tmp_file(errp);
+    if (!tmp_filename) {
         goto out;
     }
 
@@ -3771,7 +3776,6 @@  static BlockDriverState *bdrv_append_temp_snapshot(BlockDriverState *bs,
 
 out:
     qobject_unref(snapshot_options);
-    g_free(tmp_filename);
     return bs_snapshot;
 }
 
diff --git a/block/vvfat.c b/block/vvfat.c
index d6dd919683..f9bf8406d3 100644
--- a/block/vvfat.c
+++ b/block/vvfat.c
@@ -3146,10 +3146,9 @@  static int enable_write_target(BlockDriverState *bs, Error **errp)
 
     array_init(&(s->commits), sizeof(commit_t));
 
-    s->qcow_filename = g_malloc(PATH_MAX);
-    ret = get_tmp_filename(s->qcow_filename, PATH_MAX);
-    if (ret < 0) {
-        error_setg_errno(errp, -ret, "can't create temporary file");
+    s->qcow_filename = create_tmp_file(errp);
+    if (!s->qcow_filename) {
+        ret = -ENOENT;
         goto err;
     }
 
diff --git a/tests/qemu-iotests/051 b/tests/qemu-iotests/051
index f1a506518b..4c079b11e3 100755
--- a/tests/qemu-iotests/051
+++ b/tests/qemu-iotests/051
@@ -375,7 +375,8 @@  if [ "${VALGRIND_QEMU_VM}" == "y" ]; then
     _casenotrun "Valgrind needs a valid TMPDIR for itself"
 fi
 VALGRIND_QEMU_VM= \
-TMPDIR=/nonexistent run_qemu -drive driver=null-co,snapshot=on
+TMPDIR=/nonexistent run_qemu -drive driver=null-co,snapshot=on |
+    sed -e "s#'[^']*/vl\.[A-Za-z0-9]\{6\}'#SNAPSHOT_PATH#g"
 
 # Using snapshot=on together with read-only=on
 echo "info block" |
diff --git a/tests/qemu-iotests/051.out b/tests/qemu-iotests/051.out
index 441f83e41a..e5ddb03bda 100644
--- a/tests/qemu-iotests/051.out
+++ b/tests/qemu-iotests/051.out
@@ -459,7 +459,7 @@  wrote 4096/4096 bytes at offset 0
 read 4096/4096 bytes at offset 0
 4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 Testing: -drive driver=null-co,snapshot=on
-QEMU_PROG: -drive driver=null-co,snapshot=on: Could not get temporary filename: No such file or directory
+QEMU_PROG: -drive driver=null-co,snapshot=on: Could not open temporary file SNAPSHOT_PATH: No such file or directory
 
 Testing: -drive file=TEST_DIR/t.qcow2,snapshot=on,read-only=on,if=none,id=drive0
 QEMU X.Y.Z monitor - type 'help' for more information
diff --git a/tests/qemu-iotests/051.pc.out b/tests/qemu-iotests/051.pc.out
index 063e4fc584..bade1ff3b9 100644
--- a/tests/qemu-iotests/051.pc.out
+++ b/tests/qemu-iotests/051.pc.out
@@ -539,7 +539,7 @@  wrote 4096/4096 bytes at offset 0
 read 4096/4096 bytes at offset 0
 4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 Testing: -drive driver=null-co,snapshot=on
-QEMU_PROG: -drive driver=null-co,snapshot=on: Could not get temporary filename: No such file or directory
+QEMU_PROG: -drive driver=null-co,snapshot=on: Could not open temporary file SNAPSHOT_PATH: No such file or directory
 
 Testing: -drive file=TEST_DIR/t.qcow2,snapshot=on,read-only=on,if=none,id=drive0
 QEMU X.Y.Z monitor - type 'help' for more information