Merge feature/perf to master

[edwintorok]

Whats new:

• various small bugfixes: C SDK build, field typo, redo log error reporting, xentrace fix, log why master connection failed, enable backtraces earlier in xapi
• record_util backwards compatibility test
• SM to XAPI communication optimisation
• New RRD for host power usage where available via IPMI DCMI
• turn off transitive deps in dune, so we are more explicit about our build dependencies (this makes it more obvious if you want a certain module to not link with something)
• stdext switch to epoll + tests, and test that opens N file descriptors on startup
• low risk Unix.select -> Unix.sleepf changes
• some quicktests can now be run without XAPI (e.g. in unit tests)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #5760 +/- ## ======================================== + Coverage 44.8% 51.4% +6.5% ======================================== Files 16 13 -3 Lines 2210 1928 -282 ======================================== - Hits 992 991 -1 + Misses 1218 937 -281 ``` [see 4 files with indirect coverage changes](https://app.codecov.io/gh/xapi-project/xen-api/pull/5760/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | [Flag](https://app.codecov.io/gh/xapi-project/xen-api/pull/5760/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | Coverage Δ | | |---|---|---| | [python2.7](https://app.codecov.io/gh/xapi-project/xen-api/pull/5760/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | `?` | | | [python3.11](https://app.codecov.io/gh/xapi-project/xen-api/pull/5760/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project) | `51.4% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=xapi-project#carryforward-flags-in-the-pull-request-comment) to find out more.

[coveralls]

coverage: 44.887%. remained the same when pulling ce17da2e2e961951dc5cb880b088f34052d685e7 on feature/perf into e61e0acc3d04653ce203db316769c66377897869 on master.

[psafont]

turn off transitive deps in dune, so we are more explicit about our build dependencies (this makes it more obvious if you want a certain module to not link with something)

I'm surprised this doesn't cause problems in xs-opam, I've tried turning them off, but the xen-built xenctrl findlib libraries have a different name from the dummy xenctrl's (xenmmap and xenctrl.xenmmap in particular), making it impossible to build using an opam switch. Have you tested these changes in a developer opam switch?

[edwintorok]

but the xen-built xenctrl findlib libraries have a different name from the dummy xenctrl's (xenmmap and xenctrl.xenmmap in particular),

There is an explicit dependency on xenmmap now for dbgring. And the koji/opam inconsistency has been fixed long ago by https://github.com/xapi-project/xenctrl/pull/7.

I haven't tried building this in the xs-opam CI, but it builds in koji, in this CI and locally in an xs-opam based 4.14.1 opam switch.