** Description changed: + SRU Request: + + [Impact] + The current code will prevent gpu-manager from getting the correct list of alternatives. This breaks the detection system. + + [Test Case] + Install the nvidia driver and check that gpu-manager reconfigures the system properly. More specifically, there should be no "Error: no alternative found for nvidia" line in /var/log/gpu-manager.log if the driver was installed correctly. + + [Regression Potential] + Low, it is a one line change and a pretty obvious fix. + + __________________________________________________________________________ + I suppose this is a fairly significant bug, since it renders gpu-manager virtually useless. I found it in ubuntu-drivers-common 0.4.17 (which is the current version in Ubuntu 16.04), and I do not know whether it is also present in other versions. -- Symptoms -- For some reason, on my machine I frequently insert and remove my nvidia graphics adapter. My processor has an intel HD graphics adapter as well, so I rely on gpu-manager to detect my hardware configuration during boot, and update alternatives appropriately. However, since I upgraded to Ubuntu 16.04, reconfiguring my hardware makes me unable to boot to desktop. However, reverting to previous hardware configuration solves the issue. -- Analysis and proposed solution -- A quick check of symbolic links at /etc/ld.so.conf.d/x86_64-linux- gnu_GL.conf and similar confirms that when I change my hardware configuration, no changes are done to the targets of these links. Reading through gpu-manager.log I can see that it detects my hardware correctly, but it fails to configure alternatives, because: - Error: no alternative found for nvidia - Warning: no EGL alternative found for nvidia + Error: no alternative found for nvidia + Warning: no EGL alternative found for nvidia Further investigation shows that the problem is with the get_alternative_link() function, as it always returns NULL, regardless of my current hardware configuration, and function arguments. The get_alternative_link() function works by querying the list of available alternatives by running `update-alternatives` command with `--list` argument. The command is prepared by: - snprintf(command, sizeof(command), - "update-alternatives --list %s_%s_conf", - alternative_pattern, arch_path); + snprintf(command, sizeof(command), + "update-alternatives --list %s_%s_conf", + alternative_pattern, arch_path); For example, when looking for "gl" alternatives for architecture "x86_64 -linux-gnu", the resulting command will be: - update-alternatives --list gl_x86_64-linux-gnu_conf + update-alternatives --list gl_x86_64-linux-gnu_conf This command always returns an empty list, and that is correct. The command is clearly malformed, the intention was to run another command, namely: - update-alternatives --list x86_64-linux-gnu_gl_conf + update-alternatives --list x86_64-linux-gnu_gl_conf (note the order of "gl" vs "x86_64_linux_gnu") Indeed the `snprintf` used to prepare the command has it's arguments swapped. Therefore I propose to substitute the mentioned source code with: - snprintf(command, sizeof(command), - "update-alternatives --list %s_%s_conf", - arch_path, alternative_pattern); + snprintf(command, sizeof(command), + "update-alternatives --list %s_%s_conf", + arch_path, alternative_pattern); Applying the proposed change reliably fixes the bug symptoms I experienced. -- Additional comment -- For your convenience, I attached to this bug report a patch file that applies the proposed solution; the patch is intended for ubuntu-drivers-common 0.4.17 source. As far as I can tell, due to these swapped arguments gpu-manager always looks for unexisting alternatives, and therefore there is no scenario in which it would correctly configure alternatives. I suppose in this case gpu-manager always fails to serve its purpose. I find it astonishing that nobody noticed this issue yet.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1575960 Title: gpu-manager: get_alternative_link() NEVER checks for a correct alternative To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-drivers-common/+bug/1575960/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
