b/308835681 control: Support metadata outside of tmpfs

The upstream 2.4 release has support for storing engine
metadata outside of tmpfs, but it is tied to the new
MD-on-SSD feature preview. With some small adjustments
to the code, we can enable external metadata without
MD-on-SSD.

Required-githooks: true

Change-Id: If3e728a2db7a4994572bbe53c92654f2e9b01ee0
Signed-off-by: Michael MacDonald <mjmac@google.com>

src/control/server/storage/config.go

@@ -57,8 +57,9 @@ const (
 // ControlMetadata describes configuration options for control plane metadata storage on the
 // DAOS server.
 type ControlMetadata struct {
-	Path       string `yaml:"path,omitempty"`
-	DevicePath string `yaml:"device,omitempty"`
+	Path           string `yaml:"path,omitempty"`
+	DevicePath     string `yaml:"device,omitempty"`
+	DisableMdOnSSD bool   `yaml:"disable_md_on_ssd,omitempty"`
 }
 
 // Directory returns the full path to the directory where the control plane metadata is saved.
@@ -1098,7 +1099,7 @@ func (c *Config) Validate() error {
 	// backend, set to empty when no devices specified
 	if len(bdevCfgs) == 0 {
 		c.ConfigOutputPath = ""
-		if c.ControlMetadata.HasPath() {
+		if c.ControlMetadata.HasPath() && !c.ControlMetadata.DisableMdOnSSD {
 			return FaultBdevConfigControlMetadataNoRoles
 		}
 
@@ -1115,7 +1116,7 @@ func (c *Config) Validate() error {
 
 	var nvmeConfigRoot string
 	if c.ControlMetadata.HasPath() {
-		if !c.Tiers.HasBdevRoleMeta() {
+		if !c.Tiers.HasBdevRoleMeta() && !c.ControlMetadata.DisableMdOnSSD {
 			return FaultBdevConfigControlMetadataNoRoles
 		}
 		nvmeConfigRoot = c.ControlMetadata.EngineDirectory(c.EngineIdx)

src/engine/srv.c

@@ -1300,12 +1300,17 @@ dss_sys_db_init()
 	char	*sys_db_path = NULL;
 	char	*nvme_conf_path = NULL;
 
-	if (!bio_nvme_configured(SMD_DEV_TYPE_META))
-		goto db_init;
-
 	if (dss_nvme_conf == NULL) {
-		D_ERROR("nvme conf path not set\n");
-		return -DER_INVAL;
+		/* must be set if md-on-ssd is enabled */
+		if (bio_nvme_configured(SMD_DEV_TYPE_META)) {
+			D_ERROR("nvme conf path not set\n");
+			return -DER_INVAL;
+		}
+		D_STRNDUP(sys_db_path, dss_storage_path, PATH_MAX);
+		if (sys_db_path == NULL)
+			return -DER_NOMEM;
+
+		goto db_init;
 	}
 
 	D_STRNDUP(nvme_conf_path, dss_nvme_conf, PATH_MAX);
@@ -1317,7 +1322,7 @@ dss_sys_db_init()
 		return -DER_NOMEM;
 
 db_init:
-	rc = vos_db_init(bio_nvme_configured(SMD_DEV_TYPE_META) ? sys_db_path : dss_storage_path);
+	rc = vos_db_init(sys_db_path);
 	if (rc)
 		goto out;