Subject: Re: bug#31889: Filesystems must not depend on device mappings?
From: [email-masked] (Ludovic Courtès)
To: Taylan Kammer <[email-masked]>
Cc: [email-masked]
Date: Thu, 21 Jun 2018 23:55:27 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

Hi,

Taylan Kammer <[email-masked]> skribis:

>      (mapped-devices
>       (list (mapped-device
>              (source (uuid "b3d059f8-1c4f-4569-88dd-5485825b4373"))
>              (target "guixsd")
>              (type luks-device-mapping))
>             (mapped-device
>              (source (uuid "550d9258-bbbb-488c-af27-6b1fefa190ee"))
>              (target "home")
>              (type luks-device-mapping))))
>      
>      (file-systems
>       (append
>        (list (file-system
>               (device "/dev/mapper/guixsd")
>               (mount-point "/")
>               (type "ext4")
>               (dependencies mapped-devices))
>              (file-system
>               (device "/dev/mapper/home")
>               (mount-point "/home")
>               (type "ext4")
>               (dependencies mapped-devices)))
>        %base-file-systems))

[...]

> It results in the error message:
>
>     guix system: error: service 'file-system-/home' requires
>     'device-mapping-home', which is not provided by any service

[...]

> It works when both '(dependencies mapped-devices)' clauses are simply
> removed.

Yes, it’s “expected”: using “/dev/mapper/xyz” as the device is enough to
express the dependency.

When passing (dependencies mapped-devices), the effect was to each file
system depend on *both* mapped devices.  This leads to an inconsistency
because /dev/mapper/guixsd is “needed-for-boot” (i.e., set up from the
initrd), whereas /dev/mapper/home is not (i.e., set up as a Shepherd
service.)

The solution is to either use the /dev/mapper/xyz names in the ‘device’
field, or to specify only the relevant mapped device in ‘dependencies’.

Anyway, commit 68a58775e071d4b0e000b93ad121b6e64d161b79 fixes it by
doing exactly what this config asks for: setting up all the mapped
devices in the initrd.

Thanks,
Ludo’.