From 6e0ebe437bc2281db5caa6c3c066badb00afb71f Mon Sep 17 00:00:00 2001
From: Clayton Craft <clayton@craftyguy.net>
Date: Wed, 29 Apr 2026 18:46:13 -0700
Subject: [PATCH] bootctl: register fallback EFI Boot#### entry on install

This adds a second install_boot_option call to register a Boot#### entry
pointing at systemd-boot-fallback{arch}.efi, and place it immediately
after the primary entry in BootOrder.

The fallback file does not exist on the ESP on first install and is
only created on first update when the existing primary binary is
rotated to the fallback path. We register the variable anyway, so
that the entry exists in the BootOrder once the fallback file shows up.
Until then, firmware that reaches the fallback entry will fail to
load it and fall through to the next entry in BootOrder, which is
fine. install_boot_option gains a require_existing parameter so the
existing early return on a missing ESP path can be skipped for the
fallback, where a missing path is expected.

This also does a bit of refactoring by splitting the bottom part of
run_install() into a new install_variables() function that handles
registering both the primary and fallback entries.
---
 src/bootctl/bootctl-install.c | 49 +++++++++++++++++++++++++++--------
 1 file changed, 38 insertions(+), 11 deletions(-)

diff --git a/src/bootctl/bootctl-install.c b/src/bootctl/bootctl-install.c
index b20857375f..b3f8be936b 100644
--- a/src/bootctl/bootctl-install.c
+++ b/src/bootctl/bootctl-install.c
@@ -1424,6 +1424,8 @@ static int install_boot_option(
                 InstallContext *c,
                 const char *path,
                 const char *description,
+                bool require_existing,
+                uint16_t after_slot,
                 uint16_t *ret_slot) {
 
         uint16_t slot;
@@ -1447,9 +1449,9 @@ static int install_boot_option(
                         CHASE_PROHIBIT_SYMLINKS|CHASE_MUST_BE_REGULAR,
                         F_OK,
                         /* ret_path= */ NULL);
-        if (r == -ENOENT)
+        if (r == -ENOENT && require_existing)
                 return 0;
-        if (r < 0)
+        if (r < 0 && r != -ENOENT)
                 return log_error_errno(r, "Cannot access \"%s/%s\": %m", j, skip_leading_slash(path));
 
         r = find_slot(c->esp_uuid, path, &slot);
@@ -1490,7 +1492,7 @@ static int install_boot_option(
                          description);
         }
 
-        r = insert_into_order(c, slot, /* after_slot= */ UINT16_MAX);
+        r = insert_into_order(c, slot, after_slot);
         if (r < 0)
                 return r;
 
@@ -1608,6 +1610,38 @@ static int load_secure_boot_auto_enroll(
 }
 #endif
 
+static int install_variables(InstallContext *c, const char *arch) {
+        int r;
+
+        assert(c);
+
+        const char *path = strjoina("/EFI/systemd/systemd-boot", arch, ".efi");
+
+        _cleanup_free_ char *description = NULL;
+        r = pick_efi_boot_option_description(c->esp_fd, &description);
+        if (r < 0)
+                return r;
+
+        uint16_t primary_slot = UINT16_MAX;
+        r = install_boot_option(c, path, description, /* require_existing= */ true, /* after_slot= */ UINT16_MAX, &primary_slot);
+        if (r < 0)
+                return r;
+        /* If primary registration was skipped (e.g. binary not on ESP), skip the fallback too
+         * or else it would land at position 0 in BootOrder with no primary ahead of it. */
+        if (primary_slot == UINT16_MAX)
+                return 0;
+
+        const char *fallback_path = strjoina("/EFI/systemd/systemd-boot-fallback", arch, ".efi");
+
+        _cleanup_free_ char *fallback_description = strjoin("Fallback ", description);
+        if (!fallback_description)
+                return log_oom();
+
+        strshorten(fallback_description, EFI_BOOT_OPTION_DESCRIPTION_MAX);
+
+        return install_boot_option(c, fallback_path, fallback_description, /* require_existing= */ false, /* after_slot= */ primary_slot, /* ret_slot= */ NULL);
+}
+
 static int run_install(InstallContext *c) {
         int r;
 
@@ -1704,14 +1738,7 @@ static int run_install(InstallContext *c) {
                 return 0;
         }
 
-        char *path = strjoina("/EFI/systemd/systemd-boot", arch, ".efi");
-
-        _cleanup_free_ char *description = NULL;
-        r = pick_efi_boot_option_description(c->esp_fd, &description);
-        if (r < 0)
-                return r;
-
-        return install_boot_option(c, path, description, /* ret_slot= */ NULL);
+        return install_variables(c, arch);
 }
 
 int verb_install(int argc, char *argv[], uintptr_t _data, void *userdata) {