Re: [PATCH] Add dontFixup=true to derivations that build images

[Demi Marie Obenour <demiobenour@gmail.com>]

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On 10/28/25 08:57, Alyssa Ross wrote:
> Demi Marie Obenour <demiobenour@gmail.com> writes:
> 
>> This prevents lengthy and pointless scans of large image files.
>> dontFixup is added to the derivations that already used
>> unsafeDiscardReferences.  Both dontFixup and unsafeDiscardReferences are
>> added to a derivation that builds an ext4 filesystem image.
>>
>> Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
>> ---
>>  host/initramfs/default.nix             | 3 +++
>>  host/rootfs/default.nix                | 1 +
>>  img/app/default.nix                    | 2 ++
>>  release/checks/integration/default.nix | 2 ++
>>  release/combined/default.nix           | 3 +++
>>  release/combined/eosimages.nix         | 1 +
>>  release/live/default.nix               | 2 ++
>>  vm-lib/make-vm.nix                     | 1 +
>>  vm/sys/net/default.nix                 | 2 ++
>>  9 files changed, 17 insertions(+)
> 
> Good idea!

Thank you!

>> diff --git a/release/checks/integration/default.nix b/release/checks/integration/default.nix
>> index 570918613e083b0c2d7c82486544b6405ae5ea89..582a4be8df3098ddaf318b7dac60690c2f8b2304 100644
>> --- a/release/checks/integration/default.nix
>> +++ b/release/checks/integration/default.nix
>> @@ -37,6 +37,8 @@ let
>>  
>>    userData = runCommand "user-data.img" {
>>      nativeBuildInputs = [ e2fsprogs tar2ext4 ];
>> +    unsafeDiscardReferences = true;
>> +    dontFixup = true;
>>    } ''
>>      tar -Pcvf root.tar \
>>          --transform=s,^${appimage},test.appimage, ${appimage} \
> 
> This is not correct, because 1) unsafeDiscardReferences is an attribute
> set; 2) it doesn't do anything without __structuredAttrs.
> 
> https://nix.dev/manual/nix/2.26/language/advanced-attributes#adv-attr-unsafeDiscardReferences
> 
> So I'm going to make a standalone commit first that adds
> __structuredAttrs and unsafeDiscardReferences here, and then apply the
> rest of this.  I'll also tweak it to group __structuredAttrs,
> unsafeDiscardReferences, and dontFixup, so it's clear they should be
> applied together if being copied.

That worked great!  I should read the Nix manual next time.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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