[libvirt] [PATCH glib 1/2] README: formally document intended platform support targets

[Daniel P. Berrange]

Give users an indication of what distro platforms the project
intends to be buildable on. This policy will be used to decide
when it is appropriate to increase the minimum required versions
of external dependancies.

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---
 README | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++------------
 1 file changed, 55 insertions(+), 12 deletions(-)

diff --git a/README b/README
index 3108e3c..798545f 100644
--- a/README
+++ b/README
@@ -26,18 +26,61 @@ The latest official releases can be found at:
 NB: at this time, libvirt-glib is *NOT* considered API/ABI stable. Future
 releases may still include API/ABI incompatible changes.
 
-Dependencies
-============
-
-- Required:
-  - glib-2.0
-  - gobject-2.0
-  - libxml-2.0
-  - libvirt
-
-- Optional:
-  - gobject-introspection
-  - Vala (build-time only)
+Dependencies / supported platforms
+==================================
+
+The libvirt-glib projects attempts to be moderately conservative
+about updating the minimum required versions of external package
+dependencies, to strike a balance between enabling use of new
+features while minimizing inconvenience for downstream developers
+on distro platforms with specific shipped version.
+
+There are roughly two classes of Linux distro - short lifetime
+(Fedora, Ubuntu non-LTS, etc) and extended lifetime (RHEL, CentOS,
+Debian, Ubuntu LTS). Based on this classification, the libvirt-glib
+project will generally aim to ensure build support for
+
+ - Most recent 2 releases of short lifetime distros
+ - Most recent major release of extended lifetime distros,
+   with most recent 2 minor updates
+
+The project will consider RHEL, Fedora, Debian, Ubuntu LTS, Ubuntu,
+OpenSUSE and SUSE (SLES/SLED) distros to be a representative subset
+of distros when determining min required versions of external deps
+that is reasonable to target. Other distros of similar release vintage
+will typically have similar versions to at least one of these distros.
+In the case of Debian, the project may at times choose to require use
+of an update from the backports repository.
+
+As an example, as of July 1st 2015, this policy would aim to pick the
+min versions based on what's available across the following sample
+distros:
+
+ - RHEL: 7.0, 7.1
+ - Fedora: 21, 22
+ - Ubuntu LTS: 14.04 (Trusty)
+ - Ubuntu: 14.10 (Utopic), 15.04 (Vivid)
+ - Suse: 12.0
+ - OpenSUSE: 13.1, 13.2
+ - Debian: 8.0 (Jessie)
+
+At any time, it may be possible to build on versions of distros
+that are older than those implied by this policy, but the project
+will not guarantee this remains the case in future releases. The
+min required package versions of external dependancies may be
+raised in future releases based on this distro build target policy.
+
+The packages required to build libvirt-glib are
+
+ - glib-2.0
+ - gobject-2.0
+ - libxml-2.0
+ - libvirt
+
+Functionality is optionally enhanced by the following packages:
+
+ - gobject-introspection
+ - Vala (build-time only)
 
 Patches sumissions
 ==================
-- 
2.4.3