device usage based on devices file

The LVM devices file lists devices that lvm can use.  The default
file is /etc/lvm/devices/system.devices, and the lvmdevices(8)
command is used to add or remove device entries.  If the file
does not exist, or if lvm.conf includes use_devicesfile=0, then
lvm will not use a devices file.  When the devices file is in use,
the regex filter is not used, and the filter settings in lvm.conf
or on the command line are ignored.

LVM records devices in the devices file using hardware-specific
IDs, such as the WWID, and attempts to use subsystem-specific
IDs for virtual device types.  These device IDs are also written
in the VG metadata.  When no hardware or virtual ID is available,
lvm falls back using the unstable device name as the device ID.
When devnames are used, lvm performs extra scanning to find
devices if their devname changes, e.g. after reboot.

When proper device IDs are used, an lvm command will not look
at devices outside the devices file, but when devnames are used
as a fallback, lvm will scan devices outside the devices file
to locate PVs on renamed devices.  A config setting
search_for_devnames can be used to control the scanning for
renamed devname entries.

Related to the devices file, the new command option
--devices <devnames> allows a list of devices to be specified for
the command to use, overriding the devices file.  The listed
devices act as a sort of devices file in terms of limiting which
devices lvm will see and use.  Devices that are not listed will
appear to be missing to the lvm command.

Multiple devices files can be kept in /etc/lvm/devices, which
allows lvm to be used with different sets of devices, e.g.
system devices do not need to be exposed to a specific application,
and the application can use lvm on its own set of devices that are
not exposed to the system.  The option --devicesfile <filename> is
used to select the devices file to use with the command.  Without
the option set, the default system devices file is used.

Setting --devicesfile "" causes lvm to not use a devices file.

An existing, empty devices file means lvm will see no devices.

The new command vgimportdevices adds PVs from a VG to the devices
file and updates the VG metadata to include the device IDs.
vgimportdevices -a will import all VGs into the system devices file.

LVM commands run by dmeventd not use a devices file by default,
and will look at all devices on the system.  A devices file can
be created for dmeventd (/etc/lvm/devices/dmeventd.devices)  If
this file exists, lvm commands run by dmeventd will use it.

Internal implementaion:

- device_ids_read - read the devices file
  . add struct dev_use (du) to cmd->use_devices for each devices file entry
- dev_cache_scan - get /dev entries
  . add struct device (dev) to dev_cache for each device on the system
- device_ids_match - match devices file entries to /dev entries
  . match each du on cmd->use_devices to a dev in dev_cache, using device ID
  . on match, set du->dev, dev->id, dev->flags MATCHED_USE_ID
- label_scan - read lvm headers and metadata from devices
  . filters are applied, those that do not need data from the device
  . filter-deviceid skips devs without MATCHED_USE_ID, i.e.
    skips /dev entries that are not listed in the devices file
  . read lvm label from dev
  . filters are applied, those that use data from the device
  . read lvm metadata from dev
  . add info/vginfo structs for PVs/VGs (info is "lvmcache")
- device_ids_find_renamed_devs - handle devices with unstable devname ID
  where devname changed
  . this step only needed when devs do not have proper device IDs,
    and their dev names change, e.g. after reboot sdb becomes sdc.
  . detect incorrect match because PVID in the devices file entry
    does not match the PVID found when the device was read above
  . undo incorrect match between du and dev above
  . search system devices for new location of PVID
  . update devices file with new devnames for PVIDs on renamed devices
  . label_scan the renamed devs
- continue with command processing

1 files changed, 44 insertions, 4 deletions

diff --git a/tools/pvscan.c b/tools/pvscan.c
index f7aaf8ab9..6ade29bfe 100644
--- a/tools/pvscan.c
+++ b/tools/pvscan.c
@@ -1390,6 +1390,8 @@ static int _pvscan_cache_all(struct cmd_context *cmd, int argc, char **argv,
 	_online_files_remove(_vgs_online_dir);
 	_online_files_remove(_pvs_lookup_dir);
 
+	unlink_searched_devnames(cmd);
+
 	/*
 	 * pvscan --cache removes existing hints and recreates new ones.
 	 * We begin by clearing hints at the start of the command.
@@ -1443,6 +1445,7 @@ static int _pvscan_cache_args(struct cmd_context *cmd, int argc, char **argv,
 	struct dm_list pvscan_devs; /* struct device_list */
 	struct pvscan_arg *arg;
 	struct device_list *devl, *devl2;
+	int relax_deviceid_filter = 0;
 	int pv_count = 0;
 	int ret;
 
@@ -1451,7 +1454,10 @@ static int _pvscan_cache_args(struct cmd_context *cmd, int argc, char **argv,
 
 	cmd->pvscan_cache_single = 1;
 
-	dev_cache_scan();
+	if (!setup_devices(cmd)) {
+		log_error("Failed to set up devices.");
+		return_0;
+	}
 
 	/*
 	 * Get list of args.  Do not use filters.
@@ -1490,11 +1496,27 @@ static int _pvscan_cache_args(struct cmd_context *cmd, int argc, char **argv,
 
 	/*
 	 * Apply nodata filters.
-	 * bcache is not yet set up so no filters will do io.
+	 *
+	 * We want pvscan autoactivation to work when using a devices file
+	 * containing idtype=devname, in cases when the devname changes
+	 * after reboot.  To make this work, we have to relax the devices
+	 * file restrictions somewhat here in cases where the devices file
+	 * contains entries with idtype=devname: disable filter-deviceid
+	 * when applying the nodata filters here, and read the label header.
+	 * Once the label header is read, check if the label header pvid
+	 * is in the devices file, and ignore the device if it's not.
+	 * The downside of this is that pvscans from the system will read
+	 * devs belonging to other devices files.
+	 * Enable/disable this behavior with a config setting?
 	 */
-
+	 
 	log_debug("pvscan_cache_args: filter devs nodata");
 
+	if (cmd->enable_devices_file && device_ids_use_devname(cmd)) {
+		relax_deviceid_filter = 1;
+		cmd->filter_deviceid_skip = 1;
+	}
+
 	cmd->filter_nodata_only = 1;
 
 	dm_list_iterate_items_safe(devl, devl2, &pvscan_devs) {
@@ -1533,6 +1555,19 @@ static int _pvscan_cache_args(struct cmd_context *cmd, int argc, char **argv,
 			continue;
 		}
 
+		/*
+		 * filter-deviceid is not being used because of unstable devnames,
+		 * so in place of that check if the pvid is in the devices file.
+		 */
+		if (relax_deviceid_filter) {
+			if (!get_du_for_pvid(cmd, devl->dev->pvid)) {
+				log_print("pvscan[%d] %s excluded by devices file (checking PVID).",
+					  getpid(), dev_name(devl->dev));
+				dm_list_del(&devl->list);
+				continue;
+			}
+		}
+
 		/* Applies all filters, including those that need data from dev. */
 		if (!cmd->filter->passes_filter(cmd, cmd->filter, devl->dev, NULL)) {
 			log_print("pvscan[%d] %s excluded by filters: %s.", getpid(),
@@ -1541,6 +1576,9 @@ static int _pvscan_cache_args(struct cmd_context *cmd, int argc, char **argv,
 		}
 	}
 
+	if (relax_deviceid_filter)
+		cmd->filter_deviceid_skip = 0;
+
 	if (dm_list_empty(&pvscan_devs))
 		return 1;
 
@@ -1564,8 +1602,10 @@ static int _pvscan_cache_args(struct cmd_context *cmd, int argc, char **argv,
 	 * cases where this detects a change that the other methods
 	 * of detecting invalid hints doesn't catch.
 	 */
-	if (pv_count)
+	if (pv_count) {
 		invalidate_hints(cmd);
+		unlink_searched_devnames(cmd);
+	}
 
 	return ret;
 }