privilege: Add POSIX capabilities(7) support.

* gnu/system/privilege.scm (<privileged-program>): Add a field
representing the program's POSIX capabilities.
(privileged-program-capabilities): New public procedure.
* doc/guix.texi (Privileged Programs): Document it.
* gnu/build/activation.scm (activate-privileged-programs): Take a LIBCAP
package argument providing setcap(8) to apply said capabilities.
* gnu/services.scm (privileged-program->activation-gexp): Pass said
package argument where supported.  Include privileged-program-capabilities
in the compatibility hack.

1 files changed, 8 insertions, 4 deletions

diff --git a/gnu/system/privilege.scm b/gnu/system/privilege.scm
index 455a659a12..d89d5d5d1c 100644
--- a/gnu/system/privilege.scm
+++ b/gnu/system/privilege.scm
@@ -25,13 +25,14 @@
             privileged-program-setuid?
             privileged-program-setgid?
             privileged-program-user
-            privileged-program-group))
+            privileged-program-group
+            privileged-program-capabilities))
 
 ;;; Commentary:
 ;;;
 ;;; Data structures representing privileged programs: binaries with additional
-;;; permissions such as setuid/setgid.  This is meant to be used both on the
-;;; host side and at run time--e.g., in activation snippets.
+;;; permissions such as setuid/setgid, or POSIX capabilities.  This is meant to
+;;; be used both on the host side and at run time--e.g., in activation snippets.
 ;;;
 ;;; Code:
 
@@ -51,4 +52,7 @@
                  (default 0))
   ;; The group name or ID we want to set this to (defaults to root's).
   (group         privileged-program-group ;integer or string
-                 (default 0)))
+                 (default 0))
+  ;; POSIX capabilities in cap_from_text(3) form (defaults to #f: none).
+  (capabilities  privileged-program-capabilities ;string or #f
+                 (default #f)))