devices: rework libudev usage

related to config settings:
  obtain_device_info_from_udev (controls if lvm gets
    a list of devices from readdir /dev or from libudev)
  external_device_info_source (controls if lvm asks
    libudev for device information)

. Make the obtain_device_list_from_udev setting
  affect only the choice of readdir /dev vs libudev.
  The setting no longer controls if udev is used for
  device type checks.

. Change obtain_device_list_from_udev default to 0.
  This helps avoid boot timeouts due to slow libudev
  queries, avoids reported failures from
  udev_enumerate_scan_devices, and avoids delays from
  "device not initialized in udev database" errors.
  Even without errors, for a system booting with 1024 PVs,
  lvm2-pvscan times improve from about 100 sec to 15 sec,
  and the pvscan command from about 64 sec to about 4 sec.

. For external_device_info_source="none", remove all
  libudev device info queries, and use only lvm
  native device info.

. For external_device_info_source="udev", first check
  lvm native device info, then check libudev info.

. Remove sleep/retry loop when attempting libudev
  queries for device info.  udev info will simply
  be skipped if it's not immediately available.

. Only set up a libdev connection if it will be used by
  obtain_device_list_from_udev/external_device_info_source.

. For native multipath component detection, use
  /etc/multipath/wwids.  If a device has a wwid
  matching an entry in the wwids file, then it's
  considered a multipath component.  This is
  necessary to natively detect multipath
  components when the mpath device is not set up.

2 files changed, 11 insertions, 17 deletions

diff --git a/lib/config/config_settings.h b/lib/config/config_settings.h
index d66a9a3a7..fa87bea23 100644
--- a/lib/config/config_settings.h
+++ b/lib/config/config_settings.h
@@ -238,22 +238,10 @@ cfg(devices_obtain_device_list_from_udev_CFG, "obtain_device_list_from_udev", de
 	"udev support for this setting to apply.\n")
 
 cfg(devices_external_device_info_source_CFG, "external_device_info_source", devices_CFG_SECTION, 0, CFG_TYPE_STRING, DEFAULT_EXTERNAL_DEVICE_INFO_SOURCE, vsn(2, 2, 116), NULL, 0, NULL,
-	"Select an external device information source.\n"
-	"Some information may already be available in the system and LVM can\n"
-	"use this information to determine the exact type or use of devices it\n"
-	"processes. Using an existing external device information source can\n"
-	"speed up device processing as LVM does not need to run its own native\n"
-	"routines to acquire this information. For example, this information\n"
-	"is used to drive LVM filtering like MD component detection, multipath\n"
-	"component detection, partition detection and others.\n"
-	"#\n"
-	"Accepted values:\n"
-	"  none\n"
-	"    No external device information source is used.\n"
-	"  udev\n"
-	"    Reuse existing udev database records. Applicable only if LVM is\n"
-	"    compiled with udev support.\n"
-	"#\n")
+	"Enable device information from udev.\n"
+	"If set to \"udev\", lvm will supplement its own native device information\n"
+	"with information from libudev. This can potentially improve the detection\n"
+	"of MD component devices and multipath component devices.\n")
 
 cfg(devices_hints_CFG, "hints", devices_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_TYPE_STRING, DEFAULT_HINTS, vsn(2, 3, 2), NULL, 0, NULL,
 	"Use a local file to remember which devices have PVs on them.\n"
@@ -393,6 +381,10 @@ cfg(devices_scan_lvs_CFG, "scan_lvs", devices_CFG_SECTION, 0, CFG_TYPE_BOOL, DEF
 cfg(devices_multipath_component_detection_CFG, "multipath_component_detection", devices_CFG_SECTION, 0, CFG_TYPE_BOOL, DEFAULT_MULTIPATH_COMPONENT_DETECTION, vsn(2, 2, 89), NULL, 0, NULL,
 	"Ignore devices that are components of DM multipath devices.\n")
 
+cfg(devices_multipath_wwids_file_CFG, "multipath_wwids_file", devices_CFG_SECTION, CFG_DEFAULT_COMMENTED | CFG_ALLOW_EMPTY, CFG_TYPE_STRING, DEFAULT_WWIDS_FILE, vsn(2, 3, 13), NULL, 0, NULL,
+	"The path to the multipath wwids file used for multipath component detection.\n"
+	"Set this to an empty string to disable the use of the multipath wwids file.\n")
+
 cfg(devices_md_component_detection_CFG, "md_component_detection", devices_CFG_SECTION, 0, CFG_TYPE_BOOL, DEFAULT_MD_COMPONENT_DETECTION, vsn(1, 0, 18), NULL, 0, NULL,
 	"Enable detection and exclusion of MD component devices.\n"
 	"An MD component device is a block device that MD uses as part\n"
diff --git a/lib/config/defaults.h b/lib/config/defaults.h
index d5e5b3b1a..66eece53a 100644
--- a/lib/config/defaults.h
+++ b/lib/config/defaults.h
@@ -42,7 +42,7 @@
 #define DEFAULT_DEV_DIR "/dev"
 #define DEFAULT_PROC_DIR "/proc"
 #define DEFAULT_SYSTEM_ID_SOURCE "none"
-#define DEFAULT_OBTAIN_DEVICE_LIST_FROM_UDEV 1
+#define DEFAULT_OBTAIN_DEVICE_LIST_FROM_UDEV 0
 #define DEFAULT_EXTERNAL_DEVICE_INFO_SOURCE "none"
 #define DEFAULT_SYSFS_SCAN 1
 #define DEFAULT_MD_COMPONENT_DETECTION 1
@@ -327,4 +327,6 @@
 
 #define DEFAULT_SEARCH_FOR_DEVNAMES "auto"
 
+#define DEFAULT_WWIDS_FILE "/etc/multipath/wwids"
+
 #endif				/* _LVM_DEFAULTS_H */