Erm, bind mounts?

Posted Jun 7, 2023 15:26 UTC (Wed) by zuki (subscriber, #41808)
In reply to: Erm, bind mounts? by rra
Parent article: Seeking the endgame for Debian's /usr merge

> dpkg doesn't know that /bin has been aliased to /usr/bin. It has no mechanism to know this fact, and its internal architecture is fairly adverse to the whole idea, so it's proving quite difficult to add.

Meh. I believe that a generic solution would be hard. But a one-off that does a hardcoded check for /bin and /usr/bin and /sbin and /usr/sbin/ and /lib and /usr/lib and the few other prefixes that matter could be implemented without any problem.

> The dpkg maintainer also believes the way /usr-merge was done is completely wrong from a technical perspective

This is the real problem. If there was will to solve the issue, dpkg could have done this approx. 10 years ago.

Erm, bind mounts?

Posted Jun 7, 2023 16:02 UTC (Wed) by rra (subscriber, #99804) [Link] (2 responses)

> I believe that a generic solution would be hard. But a one-off that does a hardcoded check for /bin and /usr/bin and /sbin and /usr/sbin/ and /lib and /usr/lib and the few other prefixes that matter could be implemented without any problem.

You would think that, and of course we did think that, and various people tried, and failed. This turns out to create quite a lot of problems, even if you're willing to hard-code those specific exceptions, because there are complex interactions between package installation, diversions, alternatives, dpkg's existing file databases, existing features allowing directories to be symlinks to non-managed directories elsewhere on the system, and so forth.

Certainly if you think it's easy and we're all missing something, we'd love the help. But the most important part will be thorough testing of the edge cases to ensure that we didn't create new problems while trying to fix the old problem.

>> The dpkg maintainer also believes the way /usr-merge was done is completely wrong from a technical perspective
> This is the real problem. If there was will to solve the issue, dpkg could have done this approx. 10 years ago.

There was a time when I was wondering if that was the case, but the subsequent detailed analyses by people who are not the dpkg maintainer have convinced me that this is not true and the dpkg maintainer is indeed correct that this is a very invasive and non-trivial change.

Erm, bind mounts?

Posted Jun 7, 2023 17:35 UTC (Wed) by mathstuf (subscriber, #69389) [Link] (1 responses)

> But the most important part will be thorough testing of the edge cases to ensure that we didn't create new problems while trying to fix the old problem.

Not that I'm volunteering, but are these edge cases at least captured as test cases in the relevant project(s)? Or just mused about on mailing lists?

Erm, bind mounts?

Posted Jun 7, 2023 18:01 UTC (Wed) by rra (subscriber, #99804) [Link]

There has been a lot of musing and I think at least some writing in one of the working branches in conjunction with a fix in progress, but I don't know how far it's gotten. I personally haven't had the time to meaningfully contribute and therefore have been trying to stay out of people's way, so I haven't been following the implementation details that closely.

A lot of the work so far has been finding new edge cases that break and then estimating how prevalent they are in the archive.