vdev_id support for device link aliases

Add a vdev_id feature to map device names based on already defined
udev device links.  To increase the odds that vdev_id will run after
the rules it depends on, increase the vdev.rules rule number from 60
to 69.  With this change, vdev_id now provides functionality analogous
to zpool_id and zpool_layout, paving the way to retire those tools.

A defined alias takes precedence over a topology-derived name, but the
two naming methods can otherwise coexist. For example, one might name
drives in a JBOD with the sas_direct topology while naming an internal
L2ARC device with an alias.

For example, the following lines in vdev_id.conf will result in the
creation of links /dev/disk/by-vdev/{d1,d2}, each pointing to the same
target as the device link specified in the third field.

  #     by-vdev
  #     name     fully qualified or base name of device link
  alias d1       /dev/disk/by-id/wwn-0x5000c5002de3b9ca
  alias d2       wwn-0x5000c5002def789e

Also perform some minor vdev_id cleanup, such as removal of the unused
-s command line option.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #981

man/man5/vdev_id.conf.5

@@ -17,6 +17,22 @@ keyword is ignored.  Comments may optionally begin with a hash
 character.
 
 The following keywords and values are used.
+.TP
+\fIalias\fR <name> <devlink>
+Maps a device link in the /dev directory hierarchy to a new device
+name.  The udev rule defining the device link must have run prior to
+.BR vdev_id (8).
+A defined alias takes precedence over a topology-derived name, but the
+two naming methods can otherwise coexist.  For example, one might name
+drives in a JBOD with the sas_direct topology while naming an internal
+L2ARC device with an alias.
+
+\fIname\fR - the name of the link to the device that will by created in
+/dev/disk/by-vdev.
+
+\fIdevlink\fR - the name of the device link that has already been
+defined by udev.  This may be an absolute path or the base filename.
+
 .TP
 \fIchannel\fR [pci_slot] <port> <name>
 Maps a physical path to a channel name (typically representing a single
@@ -59,7 +75,7 @@ a SAS switch port number
 
 .TP
 \fIphys_per_port\fR <num>
-Specifies the number of PHY devices are associated with a SAS HBA port or SAS
+Specifies the number of PHY devices associated with a SAS HBA port or SAS
 switch port.
 .BR vdev_id (8)
 internally uses this value to determine which HBA or switch port a
@@ -150,6 +166,18 @@ definitions - one per physical path.
 	channel 86:00.0  0         B
 .br
 .P
+A configuration using device link aliases.
+.P
+.br
+	#     by-vdev
+.br
+	#     name     fully qualified or base name of device link
+.br
+	alias d1       /dev/disk/by-id/wwn-0x5000c5002de3b9ca
+.br
+	alias d2       wwn-0x5000c5002def789e
+.br
+.P
 
 .SH FILES
 .TP

man/man8/vdev_id.8

@@ -19,15 +19,20 @@ drives.  Slot numbers may also be re-mapped in case the default
 numbering is unsatisfactory.  The drive aliases will be created as
 symbolic links in /dev/disk/by-vdev.
 
-The only currently supported topologies are sas_direct and
-sas_switch.  A multipath mode is supported in which dm-mpath
-devices are handled by examining the first-listed running
-component disk as reported by the
+The currently supported topologies are sas_direct and sas_switch.  A
+multipath mode is supported in which dm-mpath devices are handled by
+examining the first-listed running component disk as reported by the
 .BR multipath (8)
 command.  In multipath mode the configuration file should contain a
 channel definition with the same name for each path to a given
 enclosure.
 
+.BR vdev_id
+also supports creating aliases based on existing udev links in the /dev
+hierarchy using the \fIalias\fR configuration file keyword.  See the
+.BR vdev_id.conf (5)
+man page for details.
+
 .SH OPTIONS
 .TP
 \fB\-c\fR <config_file>