device usage based on devices filedev-dct-deviceid-16

The devices file /etc/lvm/devices/system.devices
is a list of devices that lvm can use.
The option --devicesfile can specify a different file
name with a separate set of devices for lvm to use.
This option allows different applications to use
lvm on different sets of devices.

In most cases (with limited exceptions), lvm will not
read or use a device not listed in the devices file.
When the devices file is used, the filter-regex is
not used and the filter settings in lvm.conf are
ignored.  filter-deviceid is used when the devices
file is enabled and rejects any device that does not
match an entry in the devices file.

Set use_devicesfile = 0 in lvm.conf or set
--devicesfile "" on the command line to disable the
use of a devices file.  When disabled, lvm will see
and use any device on the system that passes the
regex filter.

A device_id, e.g. wwid or serial number from sysfs,
is a unique ID that identifies a device without
reading it.  Two devices with identical content
should have different device_ids in most common
cases.  The device_id is used in the devices file
and is included in VG metadata sections.

Each device_id has a device_id_type which indicates
where the device_id comes from, e.g. "sys_wwid"
means the device_id comes from the sysfs wwid file.
Others are sys_serial, mpath_uuid, loop_file, devname.
(devname is the device path which is a fallback when
no other proper device_id_type is available.)

filter-deviceid permits lvm to use only devices
on the system that have a device_id matching a
devices file entry.  Using the device_id, lvm can
determine the set of devices to use without reading
any devices, so the devices file will constrain lvm
in two ways:
1. it limits the devices that lvm will read.
2. it limits the devices that lvm will use.

In some uncommon cases, e.g. when devices have no
unique ID and device_id has to fall back to using
the devname, lvm may need to read all devices on the
system to determine which ones correspond to the
devices file entries.  In this case, the devices file
does not limit the devices that lvm reads, but it does
limit the devices that lvm uses.

pvcreate/vgcreate/vgextend are not constrained by
the devices file, and will look outside it to find
the new PV.  They assign the new PV a device_id
and add it to the devices file.  It is also possible
to explicitly add new PVs to the devices file before
using them in pvcreate/etc, in which case these commands
would not need to access devices outside the devices file.

vgimportdevices VG looks at all devices on the system
to find an existing VG and add its devices to the
devices file.  The command is not limited by an
existing devices file.  The command will also add
device_ids to the VG metadata if the VG does not yet
include device_ids.  vgimportdevices -a imports devices
for all accessible VGs.  Since vgimportdevices does not
limit itself to devices in an existing devices file, the
lvm.conf regex filter applies.  Adding --foreign will
import devices for foreign VGs, but device_ids are
not added to foreign VGs.  Incomplete VGs are not
imported.

The lvmdevices command manages the devices file.
The primary purpose is to edit the devices file,
but it will read PV headers to find/check PVIDs.
(It does not read, process or modify VG metadata.)

lvmdevices
. Displays devices file entries.
lvmdevices --check
. Checks devices file entries.
lvmdevices --update
. Updates devices file entries.
lvmdevices --adddev <devname>
. Adds devices_file entry (reads pv header).
lvmdevices --deldev <devname>
. Removes devices file entry.
lvmdevices --addpvid <pvid>
. Reads pv header of all devices to find <pvid>,
  and if found adds devices file entry.
lvmdevices --delpvid <pvid>
. Removes devices file entry.

The vgimportclone command has a new option --importdevices
that does the equivalent of vgimportdevices with the cloned
devices that are being imported.  The devices are "uncloned"
(new vgname and pvids) while at the same time adding the
devices to the devices file.  This allows cloned PVs to be
imported without duplicate PVs ever appearing on the system.

TODO:
device_id_type for other special devices (md, nbd, drbd)
dmeventd run commands with --devicesfile dmeventd.devices

OTHER:
allow operations with duplicate pvs if device id and size match only one dev
shortsystemid crc of systemid and written in pv header
use shortsystemid for new filter and orphan PV ownership
command to set boot flag on devices file entries needed for boot
vgchange -ay option to use devices file entries with boot flag

1 files changed, 7 insertions, 2 deletions

diff --git a/lib/device/dev-cache.h b/lib/device/dev-cache.h
index 46c86c27a..bba7bfac7 100644
--- a/lib/device/dev-cache.h
+++ b/lib/device/dev-cache.h
@@ -28,13 +28,12 @@ struct cmd_context;
 struct dev_filter {
 	int (*passes_filter) (struct cmd_context *cmd, struct dev_filter *f, struct device *dev, const char *use_filter_name);
 	void (*destroy) (struct dev_filter *f);
-	void (*wipe) (struct dev_filter *f);
+	void (*wipe) (struct cmd_context *cmd, struct dev_filter *f, struct device *dev, const char *use_filter_name);
 	void *private;
 	unsigned use_count;
 	const char *name;
 };
 
-int dev_cache_index_devs(void);
 struct dm_list *dev_cache_get_dev_list_for_vgid(const char *vgid);
 struct dm_list *dev_cache_get_dev_list_for_lvid(const char *lvid);
 
@@ -74,4 +73,10 @@ void dev_cache_failed_path(struct device *dev, const char *path);
 
 bool dev_cache_has_md_with_end_superblock(struct dev_types *dt);
 
+int get_sysfs_value(const char *path, char *buf, size_t buf_size, int error_if_no_value);
+
+int setup_devices_file(struct cmd_context *cmd);
+int setup_devices(struct cmd_context *cmd);
+int setup_device(struct cmd_context *cmd, const char *devname);
+
 #endif