From d424adce45d593d41e52294bd8f32fd33c625498 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
Date: Mon, 7 Mar 2022 18:54:50 +0100
Subject: [PATCH] basic: add new variable $SYSTEMD_OS_RELEASE to override
 location of os-release

The test for the variable is added in test-systemctl-enable because there we
can do it almost for free, and the variable is most likely to be used with
'systemctl enable --root' anyway.

(cherry picked from commit df78419d107662dd49892d76a745c294d7031d66)

Related: #2082131
---
 docs/ENVIRONMENT.md           |  5 +++++
 src/basic/os-util.c           | 16 +++++++++++-----
 test/test-systemctl-enable.sh | 12 ++++++++++--
 3 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/docs/ENVIRONMENT.md b/docs/ENVIRONMENT.md
index 71d6c55010..5e9548449c 100644
--- a/docs/ENVIRONMENT.md
+++ b/docs/ENVIRONMENT.md
@@ -43,6 +43,11 @@ All tools:
   debugging, in order to test generators and other code against specific kernel
   command lines.
 
+* `$SYSTEMD_OS_RELEASE` — if set, use this path instead of `/etc/os-release` or
+  `/usr/lib/os-release`. When operating under some root (e.g. `systemctl
+  --root=…`), the path is taken relative to the outside root. Only useful for
+  debugging.
+
 * `$SYSTEMD_FSTAB` — if set, use this path instead of `/etc/fstab`. Only useful
   for debugging.
 
diff --git a/src/basic/os-util.c b/src/basic/os-util.c
index a6e4d09473..38b2179e48 100644
--- a/src/basic/os-util.c
+++ b/src/basic/os-util.c
@@ -170,13 +170,19 @@ int open_extension_release(const char *root, const char *extension, char **ret_p
                         }
                 }
         } else {
-                FOREACH_STRING(p, "/etc/os-release", "/usr/lib/os-release") {
-                        r = chase_symlinks(p, root, CHASE_PREFIX_ROOT,
+                const char *var = secure_getenv("SYSTEMD_OS_RELEASE");
+                if (var)
+                        r = chase_symlinks(var, root, 0,
                                            ret_path ? &q : NULL,
                                            ret_fd ? &fd : NULL);
-                        if (r != -ENOENT)
-                                break;
-                }
+                else
+                        FOREACH_STRING(path, "/etc/os-release", "/usr/lib/os-release") {
+                                r = chase_symlinks(path, root, CHASE_PREFIX_ROOT,
+                                                   ret_path ? &q : NULL,
+                                                   ret_fd ? &fd : NULL);
+                                if (r != -ENOENT)
+                                        break;
+                        }
         }
         if (r < 0)
                 return r;
diff --git a/test/test-systemctl-enable.sh b/test/test-systemctl-enable.sh
index 30ba6532e7..769341129c 100644
--- a/test/test-systemctl-enable.sh
+++ b/test/test-systemctl-enable.sh
@@ -518,6 +518,14 @@ check_alias z 'z' && { echo "Expected failure because %z is not known" >&2; exit
 
 # FIXME: if there's an invalid Alias=, we shouldn't preach about empty [Install]
 
-exit 0  # yes, this is needed because the last test above fails
-
 # TODO: repeat the tests above for presets
+
+: -------SYSTEMD_OS_RELEASE relative to root------------------
+# check that os-release overwriting works as expected with root
+test -e "$root/etc/os-release"
+
+cat >"$root/etc/os-release2" <<EOF
+ID='the-id2'
+EOF
+
+SYSTEMD_OS_RELEASE="$root/etc/os-release2" check_alias o 'the-id2'