[RFC] eal: support systemd service convention for runtime directory

[Stephen Hemminger <stephen@networkplumber.org>]

Systemd.exec supports configuring the runtime directory of a service
via RuntimeDirectory=. This creates the directory with the necessary
permissions which actual service may not have if running in container.

The change to DPDK is to look for the environment RUNTIME_DIRECTORY
first and use that in preference to the fallback alternatives.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
 lib/eal/linux/eal.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/lib/eal/linux/eal.c b/lib/eal/linux/eal.c
index 60b49248388e..e729c713b393 100644
--- a/lib/eal/linux/eal.c
+++ b/lib/eal/linux/eal.c
@@ -86,25 +86,26 @@ struct lcore_config lcore_config[RTE_MAX_LCORE];
 /* used by rte_rdtsc() */
 int rte_cycles_vmware_tsc_map;
 
-static const char *default_runtime_dir = "/var/run";
-
 int
 eal_create_runtime_dir(void)
 {
-	const char *directory = default_runtime_dir;
-	const char *xdg_runtime_dir = getenv("XDG_RUNTIME_DIR");
-	const char *fallback = "/tmp";
+	const char *directory;
 	char run_dir[PATH_MAX];
 	char tmp[PATH_MAX];
 	int ret;
 
-	if (getuid() != 0) {
-		/* try XDG path first, fall back to /tmp */
-		if (xdg_runtime_dir != NULL)
-			directory = xdg_runtime_dir;
-		else
-			directory = fallback;
+	/* from RuntimeDirectory= see systemd.exec */
+	directory = getenv("RUNTIME_DIRECTORY");
+	if (directory == NULL) {
+		if (getuid() == 0)
+			directory = "/var/run";
+		else {
+			directory = getenv("XDG_RUNTIME_DIR");
+			if (directory == NULL)
+				directory = "/tmp";
+		}
 	}
+
 	/* create DPDK subdirectory under runtime dir */
 	ret = snprintf(tmp, sizeof(tmp), "%s/dpdk", directory);
 	if (ret < 0 || ret == sizeof(tmp)) {
-- 
2.30.2