From 986e734298113f9782f4ef7a238b12274bacde1e Mon Sep 17 00:00:00 2001
From: David Arroyo <david@aqwari.net>
Date: Sun, 8 May 2022 13:16:13 -0400
Subject: [PATCH] Add generic support for lower-able objects, with example.

---
 aqwari/namespace.scm |  7 +++++--
 example/my-ns.scm    | 48 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+), 2 deletions(-)
 create mode 100644 example/my-ns.scm

diff --git a/aqwari/namespace.scm b/aqwari/namespace.scm
index 3e47d29..ea43c5f 100644
--- a/aqwari/namespace.scm
+++ b/aqwari/namespace.scm
@@ -93,8 +93,7 @@ string of key=value parameters for tmpfs(5)"
     (((? string? target) (? gexp? source))
      (make-bind-mount target source))
 
-    ;; This is for convenience, so users don't have to wrap each package
-    ;; in a gexp. We also mount any propagated inputs, so they are present
+    ;; For packages, mount any propagated inputs, so they are present
     ;; in the resulting namespace.
     (((? string? target) (? package? pkg))
      (apply values
@@ -111,6 +110,10 @@ string of key=value parameters for tmpfs(5)"
     (((? string? target) ((? string? pkgname) (? package? pkg) (? string? output)))
      (make-bind-mount target (gexp (ungexp pkg output))))
 
+    ;; handles local-file, computed-file, plain-file and friends
+    (((? string? target) (? file-like? obj))
+     (bind->mount target (gexp (ungexp obj))))
+
     (((? string? target) ($ <tmpfs-mount> _ options))
      (make-tmpfs-mount target options))
 
diff --git a/example/my-ns.scm b/example/my-ns.scm
new file mode 100644
index 0000000..d4af0cf
--- /dev/null
+++ b/example/my-ns.scm
@@ -0,0 +1,48 @@
+;; To use:
+;;
+;; 	guix build -f my-ns.scm
+;;
+;; will produce the binary /gnu/store/xxx-namespace/exec
+;; you can then run
+;;
+;; 	$(guix build -f my-ns.scm)/exec /bin/sh
+;;
+;; which will construct a mount namespace based on the
+;; body of the (namespace ...) macro below, make it the
+;; new root directory, and execv(2) into /bin/sh.
+(use-modules
+  (aqwari namespace)
+  (guix gexp)
+
+  (gnu packages base)
+  (gnu packages busybox)
+  (gnu packages certs)
+  (gnu packages linux))
+
+(namespace
+  ;; You can include any number of other namespaces.
+  (include %namespace-minimal)
+
+  ;; Binding a path with no arguments binds that path in
+  ;; the parent namespace to the same path in the new
+  ;; namespace
+  (bind "/etc/resolv.conf")
+
+  ;; (bind (p1 ... pN)) is equivalent to (bind p1) ... (bind pN)
+  (bind '("/etc/gai.conf" "/etc/services"))
+  (bind '("/etc/passwd" "/etc/group" "/etc/nsswitch.conf"))
+
+  (bind "/tmp/" (tmpfs "size=100M"))
+
+  ;; You can bind a file or directory to anything with a gexp compiler.
+  (bind "/etc/hosts" (plain-file "hosts" "127.0.0.1 localhost\n"))
+
+  ;; You can bind multiple G-expressions or packages to the
+  ;; same directory. An overlay mount will be created with
+  ;; multiple lowerdir paths. This can be done with multiple
+  ;; (bind) expressions or a single (bind) expression with a
+  ;; list of sources.
+  (bind "/" (list busybox util-linux iproute))
+
+  ;; Including a tmpfs mount makes the overlay writable.
+  (bind "/" (tmpfs "nr_blocks=100k")))
-- 
2.45.2