From: raid5atemyhomework <raid5atemyhomework@protonmail.com>
To: Danny Milosavljevic <dannym@scratchpost.org>
Cc: Carlo Zancanaro <carlo@zancanaro.id.au>,
"guix-devel@gnu.org" <guix-devel@gnu.org>,
"ludo@gnu.org" <ludo@gnu.org>
Subject: Re: ZFS on Guix
Date: Wed, 10 Feb 2021 07:37:42 +0000 [thread overview]
Message-ID: <8s6nooIPFjWGbjUeq3ot7vomNW8DXsWSCXZFZcLdHg89yBk3SWXd6LC10dtTT439Uh_12IVvSImq334gpjuZbxmQ1VYD59R3W0RGA1n8Mm8=@protonmail.com> (raw)
In-Reply-To: <20210208031625.079ae4f3@scratchpost.org>
Hello Danny,
> I just wanted to say that I'm not ignoring your patch, I'm just not qualified
> to review it. I hope someone steps up to it--otherwise I can't really tell
> whether (mbegin %state-monad...) inside a random service procedure is a good
> idea.
>
> Then again, provenance-service-type does it and there it seems to be fine...
For ***this*** very specific case it is because of a random weirdness of `system-service-type`.
Specifically, the *value* of that service-type is an association list of filenames and their contained store values. However, an ***extension*** of that service-type must be a monadic action that results in an association list of filename-contents.
Here is relevant code in `gnu/services`:
```scheme
(define (system-derivation entries mextensions)
"Return as a monadic value the derivation of the 'system' directory
containing the given entries."
(mlet %store-monad ((extensions (mapm/accumulate-builds identity
mextensions)))
(lower-object
(file-union "system"
(append entries (concatenate extensions))))))
(define system-service-type
;; This is the ultimate service type, the root of the service DAG. The
;; service of this type is extended by monadic name/item pairs. These items
;; end up in the "system directory" as returned by
;; 'operating-system-derivation'.
(service-type (name 'system)
(extensions '())
(compose identity)
(extend system-derivation)
(description
"Build the operating system top-level directory, which in
turn refers to everything the operating system needs: its kernel, initrd,
system profile, boot script, and so on.")))
```
So *extensions* must be monads (due to `mapm/accumulate-builds` on the `mextensions`) but the raw value must be a simple non-monadic assoc list.
The patch moves some generated files ("kernel" and "hurd") from the value of the `system-service-type` to an extension of `system-service-type`, thus the extra `mbegin %store-monad`. It needs to be `%store-monad` since that is the monad used by the `system-derivation` function.
See:
```scheme
(define (kernel-builder-configuration->system-entry config)
"Return the kernel and hurd entries of the 'system' directory."
(mbegin %store-monad
#;...))
#;...
(define kernel-loadable-module-service-type
(service-type (name 'kernel-loadable-modules)
(extensions
(list (service-extension system-service-type
kernel-builder-configuration->system-entry))) ;; <-- OVER HERE
(compose concatenate)
(extend kernel-builder-configuration-add-modules)
(description
"Register packages containing kernel-loadable modules and adds them+to the system.")))
```
So it is not just some "random service procedure", it is because that is the interface exposed by `system-service-type` for its extensions, extensions of `system-service-type` have to yield a monadic action. `mbegin` is one of the simpler monadic actions. It is also in the "correct place" as best as I can tell, since only service types in `gnu/services.scm` dare to extend `system-service-type`.
`provenance-service-type` does this as well because it *also* extends `system-service-type`. This is basically done here simply because that is what `system-service-type` expects.
Thanks
raid5atemyhomework
prev parent reply other threads:[~2021-02-10 7:39 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-02 6:16 ZFS on Guix raid5atemyhomework
2021-01-02 6:40 ` raid5atemyhomework
2021-01-03 15:50 ` Danny Milosavljevic
[not found] ` <Kyzl4xnRrDtWbTkAmBf1i8mtSZvu-AYatdazY1NsABFAzqqi7HQl-t0d2LWAInr8n7KxGyJWfIfTWqrefrxdgWelKbr2SWc9ATV5P8zrVtw=3D@protonmail.com>
[not found] ` <DmzbKm-kVn1tCfYc4eAXeEEbj3RN28qvXJaLL6dHtBBeNdXE-e-vN-a4Y-De38H8jI5lt19mauUTz9k0JArMyOT2ciYoxKY8mXFw3xeHGqo=3D@protonmail.com>
[not found] ` <guGWV=5FuA7tRqi0SzCiial7b5W7uKlmcMRhQXIlhtzyf1Fgq91eakr8d5EQrZ2fJPJK1OqKMCJfMgE2H4SjRSph-31ms=5F2g-mFiddv9ppiaQ=3D@protonmail.com>
2021-01-04 0:50 ` raid5atemyhomework
2021-01-04 1:15 ` raid5atemyhomework
2021-01-05 11:02 ` raid5atemyhomework
2021-01-05 14:56 ` raid5atemyhomework
2021-01-06 0:59 ` Carlo Zancanaro
2021-01-06 3:50 ` raid5atemyhomework
2021-01-06 3:58 ` Carlo Zancanaro
[not found] ` <t=5Ft9LHglTTJw2Bhtd2xX4JCJeZBi5Drqg0t04vJsfRLfoENqpftZcuHO8LYi2AO05P71lbbCgQC5etCDiPsdcssJmw1pHGyCY3 gUT-9w9?= =?us-ascii?Q?=5Fo=3D@protonmail.com>
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[not found] ` <VnQXBr-z8pdZxWrb6VtIu5pv0UeG1II5uUu4Q7BU3NsJMQbxhiQyWJE4fhEIWJO3VWrjetf1SMIu4=5Fgi5r2AlY q8dADCXCD?= =?us-ascii?Q?wW30RYaJ6seA=3D@protonmail.com>
[not found] ` <BwsjjkFjW7wwYSYYp-YUhl5t1-1OtA8t3wbDftsQTZBXHNxcR2tBprzJmBYvNrMKnCeiu0d5bPz7V8IaKIdYu9NP7kDsd16z6gMPpR89-3c=3D@protonmail.com>
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[not found] ` <BwsjjkFjW7wwYSYYp-YUhl5t1-1OtA8t3wbDftsQTZBXHNxcR2tBprzJmBYvNrMKnCeiu0d5bPz7V8IaKIdYu9NP7kDsd16z6gMPpR89-3c=3D@protonmail.c om>
2021-01-06 4:41 ` raid5atemyhomework
2021-01-06 5:20 ` raid5atemyhomework
2021-01-06 15:58 ` raid5atemyhomework
2021-01-09 18:14 ` raid5atemyhomework
2021-01-10 5:17 ` raid5atemyhomework
2021-02-08 2:13 ` raid5atemyhomework
2021-02-08 3:51 ` Joshua Branson
2021-02-08 6:04 ` raid5atemyhomework
2021-02-08 6:13 ` raid5atemyhomework
2021-02-08 9:17 ` Maxime Devos
2021-02-08 9:32 ` raid5atemyhomework
2021-02-08 9:35 ` Maxime Devos
2021-02-10 8:29 ` Efraim Flashner
2021-02-08 2:16 ` Danny Milosavljevic
2021-02-10 7:37 ` raid5atemyhomework [this message]
[not found] <=5F1CLe9QSGsoMlu5WxBMXm4CbFLM=5FM9iRG1XQF9GDsK0GP208jpngdymfix4tAfoLP94mhMTt-Tx6OP2xN=5Fn78Jhx5KQzkiqPpIci=5F44C9OI=3D@protonmail.com>
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