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On 09/05/2012 12:59 PM, Fabian Groffen wrote: |
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> Seems I was to quick with the previous mail. |
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> |
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> On 04-09-2012 12:37:17 +0200, Ulrich Mueller wrote: |
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>> * Sub-slots |
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>> PMS wording: <http://git.overlays.gentoo.org/gitweb/?p=proj/pms.git;a=commit;h=5d6749ac9e5ddc5b1daaad7737b65fa81c6ece47> |
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>> Portage patch: <http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=e4ba8f36e6a4624f4fec61c7ce8bed0e3bd2fa01> |
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>> Bug: <https://bugs.gentoo.org/424429> |
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> |
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> Any pointers where we can find the argumentation what this is useful |
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> for? |
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|
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It was discussed in the "About forcing rebuilds of other packages issue" |
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[1] thread on the gentoo-dev mailing list. |
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|
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> PMS is very terse when it writes: |
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> |
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> The sub-slot is used to represent cases in which an upgrade to a new |
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> version of a package with a different sub-slot may require dependent |
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> packages to be rebuilt. When the sub-slot part is omitted from the |
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> SLOT definition, the package is considered to have an implicit |
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> sub-slot which is equal to the regular slot. |
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> |
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> While this is an inconsistency, as pointed out in previous email, it is |
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> unclear to me how this feature distinguishes from the general slot |
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> operator dependencies, which appears to achieve the same. |
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|
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The difference is that it's possible for the sub-slot to change while |
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the regular slot remains constant. I'm sure that you're familiar with |
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FEATURES=preserve-libs, and sub-slots can be used to trigger automatic |
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rebuilds in every case that triggers preserve-libs. I gave some examples |
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of how automatic rebuilds behave in my blog post about EAPI 4-slot-abi |
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[2]. In the comments of that post, I also mentioned that automatic |
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rebuilds are preferable to using @preserved-rebuild, since then help to |
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avoid the possibility of symbol collisions [3]. |
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|
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Another issue with @preserved-rebuild is that it pulls in possibly |
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irrelevant packages that are eligible for removal by --depclean. |
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Automatic rebuilds triggered by sub-slot changes to do not suffer from |
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this problem. |
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|
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> My impression here is that this tries to work around a problem where |
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> SLOT != ABI. If (and that is what I assume here) the sub-slot is used |
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> to have a major/minor-like matching criteria, it would've been more |
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> native to use dev-libs/glib:2.* and a sole slot of "2.30". |
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> In the end, it seems to be necessary to identify the various cases of |
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> breakage using versioned ELF objects, based on libtool's versioning |
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> rules, and use those as starting point to backup this feature. (Taking |
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> special care for downgrading.) |
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|
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We already discussed various kinds of syntax in the "About forcing |
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rebuilds of other packages issue" thread, and everyone seemed to be |
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happy with the sub-slot syntax that Ciaran suggested [4]. It's been |
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tested in the axs overlay for things like perl and icu sub-slot ABI |
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changes, and seems to work well. |
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|
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[1] http://thread.gmane.org/gmane.linux.gentoo.devel/77601 |
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[2] |
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http://blogs.gentoo.org/zmedico/2012/06/23/automatic-rebuilds-with-experimental-eapi-4-slot-abi/ |
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[3] |
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http://blog.flameeyes.eu/2008/06/a-few-risks-i-see-related-to-the-new-portage-2-2-preserve-libs-behaviour |
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[4] |
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http://archives.gentoo.org/gentoo-dev/msg_f0e171be0f12abac2a10069e05e43c73.xml |
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[5] https://bugs.gentoo.org/424429 |
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-- |
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Thanks, |
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Zac |
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