manager: rework generator logic

Previously generated units were always placed at the end of the search
path. With this change there will be three unit dirs instead of one, to
place generated entries at the beginning, in the middle and at the end
of the search path:

beginning: for units that need to override all configuration, regardless
of user or vendor. Example use: system-update-generator uses this to
temporarily redirect default.target.

middle: for units that need to override vendor configuration, but not
vendor configuration. Example use: /etc/fstab should override vendor
supplied configuration (think /tmp), but should not override native user
configuration.

end: does not override anything but is available as well. Possible usage
might be to convert D-Bus bus service files to native units but allowing
vendor supplied native units to win.

1 files changed, 38 insertions, 24 deletions

diff --git a/src/shared/strv.c b/src/shared/strv.c
index 18de4f8391..c8d856344c 100644
--- a/src/shared/strv.c
+++ b/src/shared/strv.c
@@ -106,28 +106,44 @@ char **strv_new_ap(const char *x, va_list ap) {
         unsigned n = 0, i = 0;
         va_list aq;
 
+        /* As a special trick we ignore all listed strings that equal
+         * (const char*) -1. This is supposed to be used with the
+         * STRV_IFNOTNULL() macro to include possibly NULL strings in
+         * the string list. */
+
         if (x) {
-                n = 1;
+                n = x == (const char*) -1 ? 0 : 1;
 
                 va_copy(aq, ap);
-                while (va_arg(aq, const char*))
+                while ((s = va_arg(aq, const char*))) {
+                        if (s == (const char*) -1)
+                                continue;
+
                         n++;
+                }
+
                 va_end(aq);
         }
 
-        if (!(a = new(char*, n+1)))
+        a = new(char*, n+1);
+        if (!a)
                 return NULL;
 
         if (x) {
-                if (!(a[i] = strdup(x))) {
-                        free(a);
-                        return NULL;
+                if (x != (const char*) -1) {
+                        a[i] = strdup(x);
+                        if (!a[i])
+                                goto fail;
+                        i++;
                 }
 
-                i++;
-
                 while ((s = va_arg(ap, const char*))) {
-                        if (!(a[i] = strdup(s)))
+
+                        if (s == (const char*) -1)
+                                continue;
+
+                        a[i] = strdup(s);
+                        if (!a[i])
                                 goto fail;
 
                         i++;
@@ -169,25 +185,27 @@ char **strv_merge(char **a, char **b) {
         if (!b)
                 return strv_copy(a);
 
-        if (!(r = new(char*, strv_length(a)+strv_length(b)+1)))
+        r = new(char*, strv_length(a) + strv_length(b) + 1);
+        if (!r)
                 return NULL;
 
-        for (k = r; *a; k++, a++)
-                if (!(*k = strdup(*a)))
+        for (k = r; *a; k++, a++) {
+                *k = strdup(*a);
+                if (!*k)
                         goto fail;
-        for (; *b; k++, b++)
-                if (!(*k = strdup(*b)))
+        }
+
+        for (; *b; k++, b++) {
+                *k = strdup(*b);
+                if (!*k)
                         goto fail;
+        }
 
         *k = NULL;
         return r;
 
 fail:
-        for (k--; k >= r; k--)
-                free(*k);
-
-        free(r);
-
+        strv_free(r);
         return NULL;
 }
 
@@ -221,11 +239,7 @@ char **strv_merge_concat(char **a, char **b, const char *suffix) {
         return r;
 
 fail:
-        for (k--; k >= r; k--)
-                free(*k);
-
-        free(r);
-
+        strv_free(r);
         return NULL;
 
 }