Subject: apt: Apt fails to choose a virtual package provider in a complex dependency tree Package: apt Version: 0.7.14ubuntu6.1 Severity: normal
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With certain dependency tree apt fails to resolve dependency problem with when
there is more than 2 providers for a virtual package. There needs to be a top
level package that depends on so called selector package. The selector package
depends on any concrete package of type a, b or c. Concrete packages all
provide and conflict a virtual package. Each concrete package depends on leaf
package leaf-a, leaf-b or leaf-c respectively. All leaf packages provide and
conflict with same virtual package.
When trying to install packages with top-level package and using leaf package
to select 'type' of packages the dependency resolution algorithm fails. This is
because problem resolution algorithm does not choose highest scored provider
but chooses first available provider that is not same as the provider that
caused the conflict. This means that 2 cases out of 3 or more will work, but
not the rest of the cases.
The problem can be solved by adding highest score consideration when choosing
provider. Problem is a bit similar to #473247, but does not solve that.
Problems are both caused because score (priority) is not considered by apt. But
they occur in different phase of package installation process.
Here is description of package dependencies.
[top] (Depends: selector)
|
[selector] (Depends: a | b | c)
/ | \
[a] [b] [c] (Provides: middle and Conflicts: middle)
/ | \
[leaf-a] [leaf-b] [leaf-c] (Provides: leaf and Conflicts: leaf)
Example of failing command is $ apt-get install -s top leaf-a
The output is following:
r...@mika-desktop:/# apt-get install -s top leaf-b
Reading package lists... Done
Building dependency tree Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
top: Depends: selector but it is not going to be installed
E: Broken packages
r...@mika-desktop:/#
I am attaching a patch that fixes this problem in conflict resolution
algorithm. The match makes the algorithm consider scores when choosing provider
for a virtual package.
-- Package-specific info:
-- (no /etc/apt/preferences present) --
-- (/etc/apt/sources.list present, but not submitted) --
-- System Information:
Debian Release: lenny/sid
APT prefers intrepid-updates
APT policy: (500, 'intrepid-updates'), (500, 'intrepid-security'), (500,
'intrepid')
Architecture: i386 (i686)
Kernel: Linux 2.6.27-16-generic (SMP w/2 CPU cores)
Locale: LANG=en_US.utf8, LC_CTYPE=en_US.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Versions of packages apt depends on:
ii libc6 2.8~20080505-0ubuntu9 GNU C Library: Shared libraries
ii libgcc1 1:4.3.2-1ubuntu12 GCC support library
ii libstdc++6 4.3.2-1ubuntu12 The GNU Standard C++ Library v3
Versions of packages apt recommends:
ii ubuntu-keyring 2008.03.04 GnuPG keys of the Ubuntu archive
-- no debconf information
apt_0.7.14ubuntu6.1.diff
Description: apt_0.7.14ubuntu6.1.diff
