Proposal of changing generating version of mdadm

["Tanska, Kinga" <kinga.tanska@intel.com>]

Hi,

recently we diagnosed few issues with 'mdadm -version' output.
Main problem is that end output varies on few conditions. We come with
simplified proposal. First let's describe current schema:

mdadm - version - date - extraversion
(example: mdadm - v4.2-rc2 - 2021-08-02 - extraversion)

or

mdadm - version - date
(example: mdadm - v4.2-rc2 - 2021-08-02).

VERSION could be taken from code (see ReadMe.c:31), but when git is
installed and .git directory is available in mdadm workspace, version
is replaced with output from # git describe HEAD command. It is assumed
that git command should return last tag from repo, which should contain
information about last release. This might not be true, especially if user
uses tags to mark internal milestones or custom mdadm spins.

The second problem is DATE, which corresponds to date of last release.
When few patches are picked onto HEAD date is not reliable. In my opinion
DATE is not needed. Usually, packages do not contain this element, e.g.
-	# git --version
		git version 2.27.0
-	# gcc --version
		gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5)
-	# yum --version
		4.2.23

To make it const and reliable, I propose removing DATE and always
use VERSION from code. VERSION shall keep general release information.
I would like to move the changeable elements into EXTRAVERSION. This
field will respect following conditions:
-	user definition first
       	(by respecting EXTRAVERSION=xxx during compilation)
-	if not defined by user, result of # git describe HEAD
-	else empty.

Example output:
mdadm - version - extraversion (example: mdadm - v4.2-rc2 - extraversion).
Thanks for any opinion about this proposition.

Regards,
Kinga Tanska