Hello! This patch adds support for service extensions that modify the "final" values of a service. This is meant to implement cross-cutting concerns as well as system-wide customization as discussed with Alex long ago: https://lists.gnu.org/archive/html/guix-devel/2015-11/msg00623.html https://lists.gnu.org/archive/html/guix-devel/2016-09/msg01505.html To summarize, a "finalization extension" (for lack of a better name) gets the final value of a service and returns a new value for that service. This is in contrast with a "normal" extension which can only contribute to the value of a target service, and not inspect the value of that target service. For example, for the /etc service, a "normal" extension can only add entries for /etc. A "finalization" extension can instead inspect and change all the /etc entries. IOW, it is a sort of a "sudo" for service extensions; it's also quite inelegant compared to the "normal" extension mechanism, but it's certainly useful. A use case is given in the second patch: we change all the PAM services to use pam_elogind.so or pam_limits.so. Likewise, the 'rename-etc-files' service below shows how to rename all the files in /etc (for illustration purposes only :-)): (define rename-etc-files (let ((rename (lambda (prefix entries) (map (match-lambda ((name . rest) (cons (string-append prefix name) rest))) entries)))) (service-type (name 'rename-etc-files) (extensions (list (service-extension etc-service-type (const '()) rename)))))) (operating-system ;; ... (services (cons* (service rename-etc-files "foo-") ...))) I think this should fulfill the need that Alex had expressed, which is to not only be able to add files to /etc, but also to have the ability to inspect and modify what goes to /etc. The first patch currently lacks doc. I'll work on it if there's consensus on the approach. Feedback welcome! Ludo'. Ludovic Courtès (2): DRAFT services: Extensions can specify a "finalization" procedure. system: pam: Remove custom API to transform PAM services. gnu/services.scm | 52 ++++++++++++++++++++++++++++++++++++++---------- gnu/services/base.scm | 33 ++++++++++++++++-------------- gnu/services/desktop.scm | 23 +++++++++++---------- gnu/system/pam.scm | 44 ++++++++-------------------------------- tests/services.scm | 34 +++++++++++++++++++++++++++++++ 5 files changed, 114 insertions(+), 72 deletions(-) -- 2.13.0