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 <[email protected]>

Makefile

@@ -53,7 +53,6 @@ install:
 	[ -d $(DESTDIR)/$(SBINDIR) ] || mkdir -p $(DESTDIR)/$(SBINDIR)
 	[ -d $(DESTDIR)/$(MANDIR) ] || mkdir -p $(DESTDIR)/$(MANDIR)
 	[ -d $(DESTDIR)/$(MANDIR)/man8 ] || mkdir -p $(DESTDIR)/$(MANDIR)/man8
-	[ -d $(DESTDIR)/$(ALTDIR) ] || mkdir -p -m 755 $(DESTDIR)/$(ALTDIR)
 	[ -d $(DESTDIR)/$(ALTDATADIR) ] || mkdir -p -m 755 $(DESTDIR)/$(ALTDATADIR)
 	[ -d $(DESTDIR)/$(SYSTEMDUTILDIR) ] || mkdir -p -m 755 $(DESTDIR)/$(SYSTEMDUTILDIR)
 

alternatives.8

@@ -214,6 +214,7 @@ A directory, by default
 containing
 .BR alternatives '
 state information.
+/etc/alternatives.admindir 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

@@ -566,6 +566,15 @@ static int fileExists(char *path) {
     return !stat(path, &sbuf);
 }
 
+static int dirExists(char *path) {
+    struct stat sbuf;
+
+    if (stat(path, &sbuf))
+            return 0;
+
+    return !!S_ISDIR(sbuf.st_mode);
+}
+
 static int facilityBelongsToUs(char *facility, const char *altDir) {
     char buf[PATH_MAX];
     if (readlink(facility, buf, sizeof(buf)) <= 0)
@@ -1321,6 +1330,10 @@ static int listServices(const char *altDir, const char *stateDir, int flags) {
     return 0;
 }
 
+static int isOSTree() {
+    return fileExists("/run/ostree-booted") || isLink("/ostree");
+}
+
 int main(int argc, const char **argv) {
     const char **nextArg;
     char *end;
@@ -1331,8 +1344,7 @@ int main(int argc, const char **argv) {
     struct alternative newAlt = {-1, {NULL, NULL, NULL}, NULL, NULL, 0, NULL};
     int flags = 0;
     char *altDir = "/etc/alternatives";
-    char *stateDir = "/var/lib/alternatives";
-    struct stat sb;
+    char *stateDir= NULL;
     struct linkSet newSet = {NULL, NULL, NULL};
 
     setlocale(LC_ALL, "");
@@ -1454,12 +1466,26 @@ int main(int argc, const char **argv) {
         }
     }
 
-    if (stat(altDir, &sb) || !S_ISDIR(sb.st_mode) || access(altDir, F_OK)) {
+    if (!dirExists(altDir)) {
         fprintf(stderr, _("altdir %s invalid\n"), altDir);
         exit(2);
     }
 
-    if (stat(stateDir, &sb) || !S_ISDIR(sb.st_mode) || access(stateDir, F_OK)) {
+    // if the stateDir is not explicitly set, we will use /var/lib/alternatives on normal systems
+    // and /etc/alternatives-admindir on OSTree systems, if the dir does not exist, we will create it
+    // if the stateDir is explicitly set, we will *not* try to create the dir and fail immediately if it does not exist
+    if (!stateDir) {
+        stateDir = "/var/lib/alternatives";
+        if (!dirExists(stateDir)) {
+            if (isOSTree())
+                stateDir = "/etc/alternatives-admindir";
+
+            if (mkdir(stateDir, 0755) < 0 && errno != EEXIST) {
+                fprintf(stderr, _("failed to create admindir: %s\n"), strerror(errno));
+                exit(2);
+            }
+        }
+    } else if (!dirExists(stateDir)) {
         fprintf(stderr, _("admindir %s invalid\n"), stateDir);
         exit(2);
     }

chkconfig.spec

@@ -19,7 +19,7 @@ Provides: /sbin/chkconfig
 %description
 Chkconfig is a basic system utility.  It updates and queries runlevel
 information for system services.  Chkconfig manipulates the numerous
-symbolic links in /etc/rc.d, to relieve system administrators of some 
+symbolic links in /etc/rc.d, to relieve system administrators of some
 of the drudgery of manually editing the symbolic links.
 
 %package -n ntsysv
@@ -95,11 +95,12 @@ mkdir -p $RPM_BUILD_ROOT/etc/chkconfig.d
 %files -n alternatives
 %license COPYING
 %dir /etc/alternatives
+%ghost %dir %attr(755, root, root) /etc/alternatives.admindir
+%ghost %dir %attr(755, root, root) /var/lib/alternatives
 %{_sbindir}/update-alternatives
 %{_sbindir}/alternatives
 %{_mandir}/*/update-alternatives*
 %{_mandir}/*/alternatives*
-%dir /var/lib/alternatives
 
 %changelog
 * Tue Jul 30 2024 Jan Macku <[email protected]> - 1.29-1