[libcamera-devel] versioning

Mon Aug 15 21:17:03 CEST 2022

Am 15.08.22 um 13:59 schrieb Eric Curtin:
> On Mon, 15 Aug 2022 at 06:29, Laurent Pinchart via libcamera-devel
> <libcamera-devel at lists.libcamera.org> wrote:
>>
>> Hi Christian,
>>
>> On Sun, Aug 14, 2022 at 11:44:05PM +0200, Christian Rauch via libcamera-devel wrote:
>>> Hi Laurent,
>>>
>>> I think the SONAME is not the primary reason for tagging/versioning.
>>> Having API versions is mainly used to check compatibility for other
>>> projects. That means that the version information has to be encoded in
>>> some project file, e.g. *.pc files. Using a SONAME is really just useful
>>> if you want to have multiple versions of a library installed or if you
>>> want to make sure that you only link a specific version.
>>
>> Bumping the SONAME is a requirement from distributions when a new
>> version breaks ABI compatibility, so I think this is very important. It
>> will also help avoiding users facing bugs due to incompatibilities
>> between the version an application was compiled against and the version
>> installed on the system.
>
> This is very important. I also am not the biggest fan of automating
> the version number bumping against a git mechanism. I have worked on
> projects like this and although it is convenient it is not ideal for
> package maintainers amongst other use cases like building against a
> tarball, etc. Fedora/EPEL are one such example where you upload the
> sources, you are not connected to the real origin repo directly at
> all.

The SONAME is important, but I still think that the versioning of the
source is even more important. Without checking for the right version,
you may encounter compilation failures. If you distribute the *.so files
with your project (e.g. in a snap, flatpak or other "container"), or
build everything from source, then the SONAME does not matter so much,
but you will still need a versioned source.
>
> So I would propose manual bumps when required and not tie specifically
> to the version control system.

This is certainly also an option and I do not have a strong opinion on this.

>
>>
>> In any case, we can version both the project, the library, and the
>> SONAME without extra complexity.
>>
>>> Am 14.08.22 um 21:01 schrieb Laurent Pinchart:
>>>> On Sun, Aug 14, 2022 at 06:01:43PM +0100, Kieran Bingham via libcamera-devel wrote:
>>>>> Quoting Christian Rauch (2022-08-14 17:25:48)
>>>>>> Am 14.08.22 um 16:12 schrieb Kieran Bingham:
>>>>>>> Quoting Christian Rauch via libcamera-devel (2022-08-13 22:14:44)
>>>>>>>> Hi all,
>>>>>>>>
>>>>>>>> I am aware that the libcamera API is unstable and because of this, there
>>>>>>>> is no versioning. I am using libcamera in another project, and it would
>>>>>>>> be helpful if I could check some version constraints in order to prevent
>>>>>>>> compiling with an incompatible API.
>>>>>>>
>>>>>>> I've been long advocating that we should have a version number, even
>>>>>>> with an unstable API. The last time I tried to push on this topic we
>>>>>>> added 0.0.0 at the very first commit which gives us some degree of
>>>>>>> patchlevel versioning for every commit.  It has taken a long time to
>>>>>>> identify clear reasons /why/ we should have more specific versions, when
>>>>>>> we have a clear unstable API, and we refer to the latest.
>>>>>>>
>>>>>>> However as you have reported here, with more API breakages recently -
>>>>>>> having other pacakges compiling against libcamera, they likely want to
>>>>>>> check what is installed. It's not always under the control and can
>>>>>>> depend upon the installation of the distro.
>>>>>>>
>>>>>>>> Would you be willing to start versioning the minor or patch-level of
>>>>>>>> libcamera? I imagine that the major version will stay at "0" until the
>>>>>>>
>>>>>>> I believe the answer is 'yes' now. But we still need to implement the
>>>>>>> 'how'.
>>>>>>>
>>>>>>> Personally - I would like to use something like abi-compliance-checker
>>>>>>> to automatically detect any ABI/API change, and automatically increment
>>>>>>> the minor patch level. libabigail looks interesting and relevant too:
>>>>>>> https://developers.redhat.com/blog/2020/04/02/how-to-write-an-abi-compliance-checker-using-libabigail#
>>>>>>>
>>>>>>> That would give us a version scheme of:
>>>>>>>
>>>>>>>  0.a[bp]i.patch
>>>>>>>
>>>>>>> Where other packages and applications could then use the second value to
>>>>>>> determine if they are compatible, (or to make conditional changes to be
>>>>>>> compilation compatible).
>>>>>>>
>>>>>>> The patch level of course would just be the number of patches since that
>>>>>>> change, and the leading version 0, would not be incremented until we
>>>>>>> were at a point that we could be comfortable stating we are 'ABI stable'.
>>>>>>>
>>>>>>>> API is stable, but that either the minor or patch-level could be
>>>>>>>> incremented (0.1, 0.2, ...) every time the API changes, or simply on a
>>>>>>>> monthly or quarterly basis.
>>>>>>>
>>>>>>> Every time I've suggested we should start making release versions, I
>>>>>>> always face push back of "What decrees a release, when should it be
>>>>>>> made?".
>>>>>>>
>>>>>>> To me time based milestones are acceptable, but don't make it
>>>>>>> easy/straightforwards to perform the version specific compilation
>>>>>>> changes required.
>>>>>>>
>>>>>>> I think they help users understand how new or old the library is though,
>>>>>>> and at least that is more helpful than our current versioning scheme
>>>>>>> where comparing 074fa98ac4e against 18d61deb3c0 is just not human
>>>>>>> readable, and doesn't convey any useful information. We have tagged our
>>>>>>> first commit as 0.0.0 which does now at least provide version strings
>>>>>>> generated by utils/gen-version.sh:
>>>>>>>
>>>>>>>  - 0.0.0+2819-18d61deb
>>>>>>>  - 0.0.0+3459-074fa98a
>>>>>>>
>>>>>>> So we could already say we could (manually) identify API/ABI changes
>>>>>>> between the patch level numbers after the + (2819, to 3459) - but that's
>>>>>>> quite labour intensive otherwise and prone to error, which is why I'd
>>>>>>> really like to see API/ABI breakages identifiable through something like
>>>>>>>
>>>>>>>  - 0.25.245-18d61deb
>>>>>>>  - 0 29.15-074fa98a
>>>>>>>
>>>>>>> Which we can then parse and extract more useful information from.
>>>>>>>
>>>>>>> I would envisage the automatic abi checker to be able to provide the
>>>>>>> 0.<abi> tags automatically on every change if run on every commit (and
>>>>>>> could be back dated right to the beginning of the tree history) ...
>>>>>>> however the point I have difficulty with is how we get those tags to
>>>>>>> then convey the correct information about the release in external
>>>>>>> systems.
>>>>>>>
>>>>>>> Is a 'tag' sufficient? or do we have to (for every 'release') manually
>>>>>>> edit the meson.build version string, or make other manual explicit
>>>>>>> changes.
>>>>>>>
>>>>>>> If we can do something around simply adding a tag on every abi/api
>>>>>>> version change, - I think that would provide the cleanest/simplest way
>>>>>>> forwards for now.
>>>>>>>
>>>>>>> Any ideas or extended comments?
>>>>
>>>> As I see it, the main reason to tag releases, from a distribution point
>>>> of view, is to increase the SONAME of the library. This will prevent
>>>> binaries linked against one version of libcamera to run with an
>>>> incompatible version. This can probably be done without modifying
>>>> meson.build, based on a similar mechanism as gen-version.sh. The project
>>>> version (in the root meson.build file) and the libcamera shared library
>>>> version can also be generated through a similar mechanism, using
>>>> run_command() directly in the project() function call for the former as
>>>> the project() function must be called before anything else. See
>>>> https://gitlab.freedesktop.org/mesa/mesa/-/blob/main/meson.build for
>>>> instance.
>>>>
>>>> Until we tag v1.0, we should use the ABI version as the SONAME. Ideally,
>>>> I'd like to use libcamera.so.0.X as the SONAME for now, not
>>>> libcamera.so.X, to allow using libcamera.so.1 once we release v1.0. I
>>>> don't know if that's a valid SONAME though.
>>>>
>>>> Automatic ABI breakage checks is nice to have, but I don't think it's a
>>>> strict requirement to tag anything. We can start with a time-based
>>>> tagging scheme (weekly for instance), with v0.0.X where X will be an
>>>> increasing index. Once ABI checks are in place, this could become
>>>> v0.X.Y. The exact versioning scheme doesn't matter much to me, as long
>>>> as it doesn't corner us for the v1.0 release.
>>>>
>>>> Kieran, if you'd like to implement now a weekly release scheme that
>>>> would use the latest tag or the .tarball-version file to populate the
>>>> project version, library version and SONAME using a v0.0.X versioning
>>>> scheme without ABI checking, I'll review the patches.
>>>>
>>>>>> I have seen CMake projects generating the version information from git.
>>>>>> This somehow works that a git command is executed as part of the build
>>>>>> process and then the stdout is parsed. Of course, this only works when
>>>>>> the source is checked out as a git repo. But I think something similar
>>>>>> could be done in meson. Then, you only need to create a new git tag and
>>>>>
>>>>> We already do this.
>>>>>
>>>>> https://git.libcamera.org/libcamera/libcamera.git/tree/meson.build#n13
>>>>>
>>>>> meson calls utils/gen-version.sh which generates a version string such
>>>>> as :
>>>>>
>>>>>   0.0.0+3829-f88d73af
>>>>>
>>>>> But it only works when the source is checked out as a git repo indeed.
>>>>>
>>>>> How does that compare for your current needs against the discussions
>>>>> above?
>>>>>
>>>>>> the next time libcamera is compiled, it would generate the version.
>>>>>>
>>>>>>>> This way, projects could check for a specific version before compiling
>>>>>>>> or search for a specific "API version". It wouldn't guarantee that the
>>>>>>>> API is compatible between versions, it's just useful to know which
>>>>>>>> version you have to use to compile a project.
>>>>>>>
>>>>>>> Agreed!
>>>>>>>
>>>>>>> It's also clear from other recent discussions that we should bump the
>>>>>>> SONAME for every ABI breakage, so again - if this can be handled through
>>>>>>> automatically detecting those breakages - I think that would help too.
>>>>>>> Having the SONAME as 0.<abi-version> as above would be a great benefit
>>>>>>> already I think.
>>
>> --
>> Regards,
>>
>> Laurent Pinchart
>>
>