ostree: move admindir to /etc/.alternatives.admindir

`ostree container commit` wipes /var and thereby erases the data in
/var/lib/alternatives; the directory used to store configs/symlinks of
alternatives.

/var is not a good place for storing such configs since it won't receive
updates on bootc images either.  We need to move to another location.

Hence, use /etc/.alternatives.admindir when running on an ostree-based
system unless /var/lib/alternatives is already present; a user may have
worked around the problem.  This way we enable alternatives to work on
ostree-based systems without breaking backwards compat.

Fixes: #9
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

Dockerfile

@@ -0,0 +1,6 @@
+FROM quay.io/fedora/fedora-bootc:40
+RUN mkdir -p /etc/.alternatives.admindir
+COPY alternatives /usr/sbin/alternatives
+RUN dnf -y install golang
+RUN ls /etc/.alternatives.admindir
+RUN go help > /dev/null

alternatives.8

@@ -214,6 +214,7 @@ A directory, by default
 containing
 .BR alternatives '
 state information.
+/etc/.alternatives.state on OSTree-based systems.
 .TP
 link group
 A set of related symlinks, intended to be updated as a group.
@@ -416,6 +417,7 @@ option.
 .TP
 .I /var/lib/alternatives/
 The default administration directory.
+/etc/.alternatives.admindir on OSTree-based systems.
 Can be overridden by the
 .B --admindir
 option.

alternatives.c

@@ -1290,6 +1290,32 @@ static int listServices(const char *altDir, const char *stateDir, int flags) {
     return 0;
 }
 
+int dirExists(const char *path) {
+    struct stat stats;
+    stat(path, &stats);
+
+    if (S_ISDIR(stats.st_mode))
+        return 1;
+
+    return 0;
+}
+
+int canUseAlternativeAdminDir() {
+    if (dirExists("/var/lib/alternatives")) {
+        return 0;
+    }
+
+    if (fileExists("/run/ostree-booted")) {
+        return 1;
+    }
+
+    if (isLink("/ostree")) {
+        return 1;
+    }
+
+    return 0;
+}
+
 int main(int argc, const char **argv) {
     const char **nextArg;
     char *end;
@@ -1304,6 +1330,10 @@ int main(int argc, const char **argv) {
     struct stat sb;
     struct linkSet newSet = {NULL, NULL, NULL};
 
+    if (canUseAlternativeAdminDir()) {
+        stateDir = "/etc/.alternatives.admindir";
+    }
+
     setlocale(LC_ALL, "");
     bindtextdomain("chkconfig", "/usr/share/locale");
     textdomain("chkconfig");

chkconfig.spec

@@ -81,9 +81,7 @@ mkdir -p $RPM_BUILD_ROOT/etc/chkconfig.d
 %{_sysconfdir}/chkconfig.d
 %{_sysconfdir}/init.d
 %{_sysconfdir}/rc.d
-%{_sysconfdir}/rc.d/init.d
 %{_sysconfdir}/rc[0-6].d
-%{_sysconfdir}/rc.d/rc[0-6].d
 %{_mandir}/*/chkconfig*
 %{_prefix}/lib/systemd/systemd-sysv-install
 
@@ -95,11 +93,12 @@ mkdir -p $RPM_BUILD_ROOT/etc/chkconfig.d
 %files -n alternatives
 %license COPYING
 %dir /etc/alternatives
+%dir /etc/.alternatives.admindir
+%ghost /var/lib/alternatives
 %{_sbindir}/update-alternatives
 %{_sbindir}/alternatives
 %{_mandir}/*/update-alternatives*
 %{_mandir}/*/alternatives*
-%dir /var/lib/alternatives
 
 %changelog
 * Fri Jun 21 2024 Jan Macku <jamacku@redhat.com> - 1.28-1