[v2] tst_tmpdir: add TST_GET_TMPDIR_ROOT() to get the TMPDIR env var

diff --git a/doc/user-guide.txt b/doc/user-guide.txt
index 656df3118..8f2418df0 100644
--- a/doc/user-guide.txt
+++ b/doc/user-guide.txt
@@ -39,6 +39,7 @@  For running LTP network tests see `testcases/network/README.md`.
                           `PATH="$PATH:$LTPROOT/testcases/bin"`
 | 'TMPDIR'              | Base directory for template directory (C: '.needs_tmpdir = 1'
                           and others, which imply it, shell: 'TST_NEEDS_TMPDIR=1').
+                          Must be an absolute path (default: '/tmp').
 | 'TST_NO_CLEANUP'      | Disable running test cleanup (defined in 'TST_CLEANUP').
 |==============================================================================
 
diff --git a/include/old/old_tmpdir.h b/include/old/old_tmpdir.h
index 9c61172fd..3e33bf043 100644
--- a/include/old/old_tmpdir.h
+++ b/include/old/old_tmpdir.h
@@ -45,6 +45,11 @@  void tst_rmdir(void);
  */
 char *tst_get_tmpdir(void);
 
+/*
+ * Returns path to the test temporary directory root (TMPDIR).
+ */
+const char *tst_get_tmpdir_root(void);
+
 /*
  * Returns 1 if temp directory was created.
  */
diff --git a/include/tst_test.h b/include/tst_test.h
index a69965b95..597c3b4a9 100644
--- a/include/tst_test.h
+++ b/include/tst_test.h
@@ -362,6 +362,11 @@  void tst_set_max_runtime(int max_runtime);
  */
 char *tst_get_tmpdir(void);
 
+/*
+ * Returns path to the test temporary directory root (TMPDIR).
+ */
+const char *tst_get_tmpdir_root(void);
+
 /*
  * Validates exit status of child processes
  */
diff --git a/lib/tst_cgroup.c b/lib/tst_cgroup.c
index 6642d6be4..50699bc63 100644
--- a/lib/tst_cgroup.c
+++ b/lib/tst_cgroup.c
@@ -645,10 +645,7 @@  static void cgroup_mount_v2(void)
 {
 	int ret;
 	char mnt_path[PATH_MAX];
-	const char *tmpdir = getenv("TMPDIR");
-
-	if (!tmpdir)
-		tmpdir = "/tmp";
+	const char *tmpdir = tst_get_tmpdir_root();
 
 	sprintf(mnt_path, "%s/%s%s",
 		tmpdir, cgroup_mount_ltp_prefix, cgroup_v2_ltp_mount);
@@ -698,10 +695,7 @@  static void cgroup_mount_v1(struct cgroup_ctrl *const ctrl)
 {
 	char mnt_path[PATH_MAX];
 	int made_dir = 0;
-	const char *tmpdir = getenv("TMPDIR");
-
-	if (!tmpdir)
-		tmpdir = "/tmp";
+	const char *tmpdir = tst_get_tmpdir_root();
 
 	if (ctrl->ctrl_indx == CTRL_BLKIO && controllers[CTRL_IO].ctrl_root) {
 		tst_res(TCONF,
diff --git a/lib/tst_supported_fs_types.c b/lib/tst_supported_fs_types.c
index 7781f94c3..d4911fa3b 100644
--- a/lib/tst_supported_fs_types.c
+++ b/lib/tst_supported_fs_types.c
@@ -74,14 +74,11 @@  int tst_fs_in_skiplist(const char *fs_type, const char *const *skiplist)
 static enum tst_fs_impl has_kernel_support(const char *fs_type)
 {
 	static int fuse_supported = -1;
-	const char *tmpdir = getenv("TMPDIR");
+	const char *tmpdir = tst_get_tmpdir_root();
 	char buf[128];
 	char template[PATH_MAX];
 	int ret;
 
-	if (!tmpdir)
-		tmpdir = "/tmp";
-
 	snprintf(template, sizeof(template), "%s/mountXXXXXX", tmpdir);
 	if (!mkdtemp(template))
 		tst_brk(TBROK | TERRNO, "mkdtemp(%s) failed", template);
diff --git a/lib/tst_tmpdir.c b/lib/tst_tmpdir.c
index 6e38ae977..d1419a1a4 100644
--- a/lib/tst_tmpdir.c
+++ b/lib/tst_tmpdir.c
@@ -122,6 +122,21 @@  char *tst_get_tmpdir(void)
 	return ret;
 }
 
+const char *tst_get_tmpdir_root(void)
+{
+	const char *env_tmpdir = getenv("TMPDIR");
+
+	if (!env_tmpdir)
+		env_tmpdir = TEMPDIR;
+
+	if (env_tmpdir[0] != '/') {
+		tst_brkm(TBROK, NULL, "You must specify an absolute "
+				"pathname for environment variable TMPDIR");
+		return NULL;
+	}
+	return env_tmpdir;
+}
+
 const char *tst_get_startwd(void)
 {
 	return test_start_work_dir;
@@ -245,31 +260,16 @@  static int rmobj(const char *obj, char **errmsg)
 void tst_tmpdir(void)
 {
 	char template[PATH_MAX];
-	char *env_tmpdir;
-	char *errmsg, *c;
+	const char *env_tmpdir;
+	char *errmsg;
 
 	/*
 	 * Create a template for the temporary directory.  Use the
 	 * environment variable TMPDIR if it is available, otherwise
 	 * use our default TEMPDIR.
 	 */
-	env_tmpdir = getenv("TMPDIR");
-	if (env_tmpdir) {
-		c = strchr(env_tmpdir, '/');
-		/*
-		 * Now we force environment variable TMPDIR to be an absolute
-		 * pathname, which dose not make much sense, but it will
-		 * greatly simplify code in tst_rmdir().
-		 */
-		if (c != env_tmpdir) {
-			tst_brkm(TBROK, NULL, "You must specify an absolute "
-				 "pathname for environment variable TMPDIR");
-			return;
-		}
-		snprintf(template, PATH_MAX, "%s/%.3sXXXXXX", env_tmpdir, TCID);
-	} else {
-		snprintf(template, PATH_MAX, "%s/%.3sXXXXXX", TEMPDIR, TCID);
-	}
+	env_tmpdir = tst_get_tmpdir_root();
+	snprintf(template, PATH_MAX, "%s/%.3sXXXXXX", env_tmpdir, TCID);
 
 	/* Make the temporary directory in one shot using mkdtemp. */
 	if (mkdtemp(template) == NULL) {
diff --git a/testcases/kernel/security/filecaps/filecaps_common.h b/testcases/kernel/security/filecaps/filecaps_common.h
index 920f6ac6a..0f011868e 100644
--- a/testcases/kernel/security/filecaps/filecaps_common.h
+++ b/testcases/kernel/security/filecaps/filecaps_common.h
@@ -1,5 +1,6 @@ 
 #include <limits.h>
 #include <stdlib.h>
+#include <old_tmpdir.h>
 
 static char *fifofile;
 
@@ -9,10 +10,8 @@  static const char *get_caps_fifo(void)
 		fifofile = getenv("FIFOFILE");
 
 		if (!fifofile) {
-			const char *tmpdir = getenv("TMPDIR");
+			const char *tmpdir = tst_get_tmpdir_root();
 
-			if (!tmpdir)
-				tmpdir = "/tmp";
 			fifofile = malloc(PATH_MAX);
 			snprintf(fifofile, PATH_MAX, "%s/caps_fifo", tmpdir);
 		}
diff --git a/testcases/kernel/syscalls/getcwd/getcwd02.c b/testcases/kernel/syscalls/getcwd/getcwd02.c
index e843a4896..cb111a698 100644
--- a/testcases/kernel/syscalls/getcwd/getcwd02.c
+++ b/testcases/kernel/syscalls/getcwd/getcwd02.c
@@ -42,28 +42,6 @@  static int dir_exists(const char *dirpath)
 	return 0;
 }
 
-static const char *get_tmpdir_path(void)
-{
-	char *tmpdir = "/tmp";
-
-	if (dir_exists(tmpdir))
-		goto done;
-
-	/* fallback to $TMPDIR */
-	tmpdir = getenv("TMPDIR");
-	if (!tmpdir)
-		tst_brk(TBROK | TERRNO, "Failed to get $TMPDIR");
-
-	if (tmpdir[0] != '/')
-		tst_brk(TBROK, "$TMPDIR must be an absolute path");
-
-	if (!dir_exists(tmpdir))
-		tst_brk(TBROK | TERRNO, "TMPDIR '%s' doesn't exist", tmpdir);
-
-done:
-	return tmpdir;
-}
-
 static void verify_getcwd(unsigned int n)
 {
 	struct t_case *tc = &tcases[n];
@@ -92,7 +70,10 @@  end:
 
 static void setup(void)
 {
-	const char *tmpdir = get_tmpdir_path();
+	const char *tmpdir = tst_get_tmpdir_root();
+
+	if (!dir_exists(tmpdir))
+		tst_brk(TBROK | TERRNO, "TMPDIR '%s' doesn't exist", tmpdir);
 
 	SAFE_CHDIR(tmpdir);