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From 99ca5b681fceedd010b2616b1248a483f4bfbd97 Mon Sep 17 00:00:00 2001
From: Kairui Song <kasong@redhat.com>
Date: Wed, 13 Jan 2021 00:04:53 +0800
Subject: [PATCH] initrd: extend SYSTEMD_IN_INITRD to accept non-ramfs rootfs

Sometimes, non-ramfs initrd root are useful. Eg, for kdump, because
initramfs is memory consuming, so mount a compressed image in earlier
initrd, chroot into it then let systemd do the rest of job is a good
solution.

But systemd doesn't recognize the initrd environment if rootfs is not a
temporary fs. This is a reasonable check, because switch-root in initrd
will wipe the whole rootfs, will be a disaster if there are any
misdetect.

So extend SYSTEMD_IN_INITRD environment variable, now it accepts boolean
value and two extra keyword, "auto" and "lenient". "auto" is same as
before, and it's the default value. "lenient" will let systemd bypass
the rootfs check.

(cherry picked from commit db4c45cf4f10ca094b9e9570b758abd445d65381)

Related: #1959339
---
 doc/ENVIRONMENT.md |  8 ++++++++
 src/basic/util.c   | 28 +++++++++++++++++++++++++---
 2 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/doc/ENVIRONMENT.md b/doc/ENVIRONMENT.md
index 36b649afe1..8d7ce6ae2c 100644
--- a/doc/ENVIRONMENT.md
+++ b/doc/ENVIRONMENT.md
@@ -37,6 +37,14 @@ All tools:
   useful for debugging, in order to test generators and other code against
   specific kernel command lines.
 
+* `$SYSTEMD_IN_INITRD=[auto|lenient|0|1]` — if set, specifies initrd detection
+  method. Defaults to `auto`. Behavior is defined as follows:
+  `auto`: Checks if `/etc/initrd-release` exists, and a temporary fs is mounted
+          on `/`. If both conditions meet, then it's in initrd.
+  `lenient`: Similiar to `auto`, but the rootfs check is skipped.
+  `0|1`: Simply overrides initrd detection. This is useful for debugging and
+         testing initrd-only programs in the main system.
+
 * `$SYSTEMD_EMOJI=0` — if set, tools such as "systemd-analyze security" will
   not output graphical smiley emojis, but ASCII alternatives instead. Note that
   this only controls use of Unicode emoji glyphs, and has no effect on other
diff --git a/src/basic/util.c b/src/basic/util.c
index b443e639f3..59bcf7b00c 100644
--- a/src/basic/util.c
+++ b/src/basic/util.c
@@ -130,11 +130,14 @@ int prot_from_flags(int flags) {
 }
 
 bool in_initrd(void) {
+        int r;
+        const char *e;
+        bool lenient = false;
 
         if (saved_in_initrd >= 0)
                 return saved_in_initrd;
 
-        /* We make two checks here:
+        /* We have two checks here:
          *
          * 1. the flag file /etc/initrd-release must exist
          * 2. the root file system must be a memory file system
@@ -142,10 +145,29 @@ bool in_initrd(void) {
          * The second check is extra paranoia, since misdetecting an
          * initrd can have bad consequences due the initrd
          * emptying when transititioning to the main systemd.
+         *
+         * If env var $SYSTEMD_IN_INITRD is not set or set to "auto",
+         * both checks are used. If it's set to "lenient", only check
+         * 1 is used. If set to a booleen value, then the boolean
+         * value is returned.
          */
 
-        saved_in_initrd = access("/etc/initrd-release", F_OK) >= 0 &&
-                          path_is_temporary_fs("/") > 0;
+        e = secure_getenv("SYSTEMD_IN_INITRD");
+        if (e) {
+                if (streq(e, "lenient"))
+                        lenient = true;
+                else if (!streq(e, "auto")) {
+                        r = parse_boolean(e);
+                        if (r >= 0) {
+                                saved_in_initrd = r > 0;
+                                return saved_in_initrd;
+                        }
+                        log_debug_errno(r, "Failed to parse $SYSTEMD_IN_INITRD, ignoring: %m");
+                }
+        }
+
+        saved_in_initrd = (lenient || path_is_temporary_fs("/") > 0) &&
+                          access("/etc/initrd-release", F_OK) >= 0;
 
         return saved_in_initrd;
 }