Re: [PATCH] buildchroot: Allow downgrades when installing packages

["Maxim Yu. Osipov" <mosipov@ilbers.de>]

Hi Jan,

Tried to apply the patch - CI build failed.

See for details:
http://isar-build.org:8080/job/isar_mosipov_next/164/console

Regards,
Maxim.

On 3/19/19 11:31 AM, Jan Kiszka wrote:
> On 19.03.19 11:10, Baurzhan Ismagulov wrote:
>> On Mon, Feb 25, 2019 at 12:08:23PM +0100, Jan Kiszka wrote:
>>> Removing -rcX from a version string is lexically a downgrade, 
>>> logically not.
>>> I'm not that sure if you can compensate this.
>>
>> Debian uses tilde for that, e.g. 1.0~rc1-1+deb9u2. This is addressed in
>> https://www.debian.org/doc/debian-policy/ch-controlfields.html#version:
>>
>>    "First the initial part of each string consisting entirely of 
>> non-digit
>>    characters is determined. These two parts (one of which may be 
>> empty) are
>>    compared lexically. If a difference is found it is returned. The 
>> lexical
>>    comparison is a comparison of ASCII values modified so that all the 
>> letters
>>    sort earlier than all the non-letters and so that a tilde sorts before
>>    anything, even the end of a part. For example, the following parts 
>> are in
>>    sorted order from earliest to latest: ~~, ~~a, ~, the empty part, 
>> a. [7]
>>
>>    [7] One common use of ~ is for upstream pre-releases. For example,
>>        1.0~beta1~svn1245 sorts earlier than 1.0~beta1, which sorts 
>> earlier than
>>        1.0."
>>
> 
> Good to know. We will have to educate people coming from OE about this 
> non-intuitive deviation from how things work over there.
> 
>>
>>> Anyway, a real downgrade is a valid development scenario as well for our
>>> isar-apt.
>>
>> Downgrade is supported by the packaging toolchain (dpkg / apt), but 
>> not by the
>> distribution (packages themselves, notably postinst, etc.).
>> https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_emergency_downgrading 
>>
>> says:
>>
>>    "Downgrading is not officially supported by the Debian by design. 
>> It should
>>    be done only as a part of emergency recovery process. Despite of this
>>    situation, it is known to work well in many incidents. For critical 
>> systems,
>>    you should backup all important data on the system after the recovery
>>    operation and re-install the new system from the scratch.
>>
>>    You may be lucky to downgrade from newer archive to older archive 
>> to recover
>>    from broken system upgrade by manipulating candidate version..."
>>
>> So I'd be reluctant to do that by default. What about extracting the apt
>> options into a config file, where the user may add his options?
> 
> I don't see that we should add a redundant, counter-intuitive option. 
> The user already clearly expressed that packages of choice should be 
> installed. This is what whole Isar is about: customization. Moreover, 
> the user will get exactly that by doing a clean rebuild.
> 
> So, please merge.
> 
> Jan
> 


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