[OE-core] [PATCH v2] update-alternatives: Allow using relative symlinks

[Böszörményi Zoltán]

The alternative links are invalid during do_rootfs.

Add a new ALTERNATIVE_TARGET_RELATIVE family of variables to
conditionally make these links valid.

v2: Fix the case when the link source and target are not in
    the same directory.

Signed-off-by: Böszörményi Zoltán <zboszor at pr.hu>
---
 meta/classes/update-alternatives.bbclass | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/meta/classes/update-alternatives.bbclass b/meta/classes/update-alternatives.bbclass
index aa01058cf9..540bec94e2 100644
--- a/meta/classes/update-alternatives.bbclass
+++ b/meta/classes/update-alternatives.bbclass
@@ -47,6 +47,15 @@
 # the need to rename alternative files in the do_install step, but still
 # supports it if necessary for some reason.)
 #
+# The default to use relative link for all targets
+# ALTERNATIVE_TARGET_RELATIVE = "1"
+#
+# A non-default setting to use relative link for a target
+# ALTERNATIVE_TARGET_RELATIVE[name] = "1"
+#
+# A package specific setting to use relative link for a target
+# ALTERNATIVE_TARGET_RELATIVE_<pkg>[name] = "1"
+#
 # The default priority for any alternatives
 # ALTERNATIVE_PRIORITY = "priority"
 #
@@ -214,6 +223,10 @@ python populate_packages_updatealternatives () {
             # Sometimes alt_target is specified as relative to the link name.
             alt_target   = os.path.join(os.path.dirname(alt_link), alt_target)
 
+            # Whether to use relative symlink target
+            alt_relative = d.getVarFlag('ALTERNATIVE_TARGET_RELATIVE_%s' % pkg, alt_name) or d.getVarFlag('ALTERNATIVE_TARGET_RELATIVE', alt_name)
+            alt_relative = alt_relative or d.getVar('ALTERNATIVE_TARGET_RELATIVE_%s' % pkg) or d.getVar('ALTERNATIVE_TARGET_RELATIVE')
+
             alt_priority = d.getVarFlag('ALTERNATIVE_PRIORITY_%s' % pkg,  alt_name) or d.getVarFlag('ALTERNATIVE_PRIORITY',  alt_name)
             alt_priority = alt_priority or d.getVar('ALTERNATIVE_PRIORITY_%s' % pkg) or d.getVar('ALTERNATIVE_PRIORITY')
 
@@ -229,8 +242,15 @@ python populate_packages_updatealternatives () {
             # Default to generate shell script.. eventually we may want to change this...
             alt_target = os.path.normpath(alt_target)
 
-            alt_setup_links  += '\tupdate-alternatives --install %s %s %s %s\n' % (alt_link, alt_name, alt_target, alt_priority)
-            alt_remove_links += '\tupdate-alternatives --remove  %s %s\n' % (alt_name, alt_target)
+            if alt_relative and os.path.dirname(alt_target) == os.path.dirname(alt_link):
+                alt_target_final = os.path.basename(alt_target)
+            elif alt_relative:
+                alt_target_final = os.path.join(os.path.join(*['..'] * len(list(filter(None, os.path.dirname(alt_link).split('/'))))), *list(filter(None, alt_target.split('/'))))
+            else:
+                alt_target_final = alt_target
+
+            alt_setup_links  += '\tupdate-alternatives --install %s %s %s %s\n' % (alt_link, alt_name, alt_target_final, alt_priority)
+            alt_remove_links += '\tupdate-alternatives --remove  %s %s\n' % (alt_name, alt_target_final)
 
         if alt_setup_links:
             # RDEPENDS setup
-- 
2.19.1