[gnome-continuous-yocto/gnomeostree-3.28-rocko: 4031/8267] lib/oe/rootfs: reliably handle alternative symlinks

[Emmanuele Bassi <ebassi src gnome org>]

commit 08fd7c4fc27b83f921d76dbb152f83394f68f1c2
Author: André Draszik <adraszik tycoint com>
Date:   Thu Jan 12 10:34:39 2017 +0000

    lib/oe/rootfs: reliably handle alternative symlinks
    
    When removing unneeded packages from a (read-only) rootfs
    during rootfs creation, alternative symlinks from those
    packages may or may not be removed.
    
    The reason is as follows:
    
    update-alternatives(-native) is used during package
    installation as part of the image creation. It uses
    a database which contains entries for all the
    alternative symlinks possible, and the -native version
    uses the target's database by means of $OPKG_OFFLINE_ROOT,
    i.e. the rootfs we're in the process of creating.
    
    Once the rootfs has been created, OE removes certain
    packages because we have a read-only rootfs - in
    particular ROOTFS_RO_UNNEEDED which includes
    VIRTUAL-RUNTIME_update-alternatives, i.e. the
    update-alternatives. Recently, a change was made in
    OE, where uninstallation of update-alternatives from the
    rootfs causes removal of its database, too, to save space
    (700KiB (uncompressed) in a busybox system)
      b24a63d71b517af701dfedbc7f7b541d25af708f
      
http://git.openembedded.org/openembedded-core/commit/meta/recipes-devtools/opkg-utils/opkg-utils_git.bb?id=b24a63d71b517af701dfedbc7f7b541d25af708f
    
    Following from that, if update-alternatives is removed
    from the target file system, update-alternatives-native
    has no database anymore, meaning it can't manage any of
    the alternative symlinks anymore.
    
    Because the order of packages to uninstall is
    non-deterministic, and update-alternatives could well
    be removed before any packages that use the mechanism
    provided, sometimes the extra symlinks are removed,
    sometimes not.
    
    By sorting the list of packages to be removed such that
    update-alternatives is removed last, we can ensure that
    that tings work reliably. (Certainly opkg seems to
    uninstall packages in the order given on the command
    line.)
    
    [YOCTO #10916]
    
    (From OE-Core rev: 5263dd3eac9d9fbdb7ef654d0cd532c192baed16)
    
    Signed-off-by: André Draszik <adraszik tycoint com>
    Signed-off-by: Ross Burton <ross burton intel com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 meta/lib/oe/rootfs.py |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/meta/lib/oe/rootfs.py b/meta/lib/oe/rootfs.py
index 274ddb8..5b842ba 100644
--- a/meta/lib/oe/rootfs.py
+++ b/meta/lib/oe/rootfs.py
@@ -262,7 +262,12 @@ class Rootfs(object, metaclass=ABCMeta):
             # Remove components that we don't need if it's a read-only rootfs
             unneeded_pkgs = self.d.getVar("ROOTFS_RO_UNNEEDED").split()
             pkgs_installed = image_list_installed_packages(self.d)
-            pkgs_to_remove = [pkg for pkg in pkgs_installed if pkg in unneeded_pkgs]
+            # Make sure update-alternatives is last on the command line, so
+            # that it is removed last. This makes sure that its database is
+            # available while uninstalling packages, allowing alternative
+            # symlinks of packages to be uninstalled to be managed correctly.
+            provider = self.d.getVar("VIRTUAL-RUNTIME_update-alternatives")
+            pkgs_to_remove = sorted([pkg for pkg in pkgs_installed if pkg in unneeded_pkgs], key=lambda x: x 
== provider)
 
             if len(pkgs_to_remove) > 0:
                 self.pm.remove(pkgs_to_remove, False)