zdev: Implement support for early device configuration

Enable user to specify that a device should be configured early, that is
during the initial RAM-disk boot phase. This may be necessary, e.g. to
override auto-configuration for a device which is also applied during
that boot phase. It may also be used to manually specify devices that
are required to access the root file system, such as networking devices.

Users can mark devices as requiring early configuration by specifying
a value of 1 for the newly added internal attribute zdev:early:

 # chzdev dasd-eckd 0.0.1234 -p zdev:early=1

This can be changed back by removing the attribute setting, or by
setting the attribute value to 0:

 # chzdev dasd-eckd 0.0.1234 -p -r zdev:early

or

 # chzdev dasd-eckd 0.0.1234 -p zdev:early=0

Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdev/man/chzdev.8

@@ -334,6 +334,35 @@ a specific attribute.
 .PP
 .
 .
+.SS "Special settings"
+The following special settings affect how devices are handled by chzdev:
+.PP
+.
+.BR zdev:early =0|1
+.RS 4
+Control in which stage of the boot process a device is activated:
+.TP 4
+.B 0
+Device is activated normally during boot (default).
+.PP
+.TP 4
+.B 1
+Device is activated early in the boot process, by the initial RAM-disk.
+.PP
+Specify a value of 1 for this attribute in any of the following situations:
+.TP 4
+\(bu
+To ensure that your settings override auto-configuration settings.
+.PP
+.TP 4
+\(bu
+To ensure that a device required to access the root file system is correctly
+enabled during boot. An example would be a networking device, or a device that
+is intended to extend a logical volume that provides the root file system.
+.PP
+.RE
+.
+.
 .SH ACTIONS
 You can use one of the action options listed below to specify the
 .B main tool action