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.

5 files changed, 175 insertions, 82 deletions

diff --git a/src/shared/install.c b/src/shared/install.c
index d6644e580f..7e4f666952 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -60,7 +60,8 @@ static int lookup_paths_init_from_scope(LookupPaths *paths, UnitFileScope scope)
 
         return lookup_paths_init(paths,
                                  scope == UNIT_FILE_SYSTEM ? MANAGER_SYSTEM : MANAGER_USER,
-                                 scope == UNIT_FILE_USER);
+                                 scope == UNIT_FILE_USER,
+                                 NULL, NULL, NULL);
 }
 
 static int get_config_path(UnitFileScope scope, bool runtime, const char *root_dir, char **ret) {
diff --git a/src/shared/path-lookup.c b/src/shared/path-lookup.c
index 41ebc7f5b3..32ddb38865 100644
--- a/src/shared/path-lookup.c
+++ b/src/shared/path-lookup.c
@@ -34,7 +34,8 @@
 int user_config_home(char **config_home) {
         const char *e;
 
-        if ((e = getenv("XDG_CONFIG_HOME"))) {
+        e = getenv("XDG_CONFIG_HOME");
+        if (e) {
                 if (asprintf(config_home, "%s/systemd/user", e) < 0)
                         return -ENOMEM;
 
@@ -42,7 +43,8 @@ int user_config_home(char **config_home) {
         } else {
                 const char *home;
 
-                if ((home = getenv("HOME"))) {
+                home = getenv("HOME");
+                if (home) {
                         if (asprintf(config_home, "%s/.config/systemd/user", home) < 0)
                                 return -ENOMEM;
 
@@ -53,7 +55,11 @@ int user_config_home(char **config_home) {
         return 0;
 }
 
-static char** user_dirs(void) {
+static char** user_dirs(
+                const char *generator,
+                const char *generator_early,
+                const char *generator_late) {
+
         const char * const config_unit_paths[] = {
                 USER_CONFIG_UNIT_PATH,
                 "/etc/systemd/user",
@@ -89,15 +95,19 @@ static char** user_dirs(void) {
 
         home = getenv("HOME");
 
-        if ((e = getenv("XDG_CONFIG_DIRS")))
-                if (!(config_dirs = strv_split(e, ":")))
+        e = getenv("XDG_CONFIG_DIRS");
+        if (e) {
+                config_dirs = strv_split(e, ":");
+                if (!config_dirs)
                         goto fail;
+        }
 
         /* We don't treat /etc/xdg/systemd here as the spec
          * suggests because we assume that that is a link to
          * /etc/systemd/ anyway. */
 
-        if ((e = getenv("XDG_DATA_HOME"))) {
+        e = getenv("XDG_DATA_HOME");
+        if (e) {
                 if (asprintf(&data_home, "%s/systemd/user", e) < 0)
                         goto fail;
 
@@ -116,57 +126,87 @@ static char** user_dirs(void) {
                 (void) symlink("../../../.config/systemd/user", data_home);
         }
 
-        if ((e = getenv("XDG_DATA_DIRS")))
+        e = getenv("XDG_DATA_DIRS");
+        if (e)
                 data_dirs = strv_split(e, ":");
         else
                 data_dirs = strv_new("/usr/local/share",
                                      "/usr/share",
                                      NULL);
-
         if (!data_dirs)
                 goto fail;
 
         /* Now merge everything we found. */
+        if (generator_early) {
+                t = strv_append(r, generator_early);
+                if (!t)
+                        goto fail;
+                strv_free(r);
+                r = t;
+        }
+
         if (config_home) {
-                if (!(t = strv_append(r, config_home)))
+                t = strv_append(r, config_home);
+                if (!t)
                         goto fail;
                 strv_free(r);
                 r = t;
         }
 
         if (!strv_isempty(config_dirs)) {
-                if (!(t = strv_merge_concat(r, config_dirs, "/systemd/user")))
+                t = strv_merge_concat(r, config_dirs, "/systemd/user");
+                if (!t)
                         goto finish;
                 strv_free(r);
                 r = t;
         }
 
-        if (!(t = strv_merge(r, (char**) config_unit_paths)))
+        t = strv_merge(r, (char**) config_unit_paths);
+        if (!t)
                 goto fail;
         strv_free(r);
         r = t;
 
+        if (generator) {
+                t = strv_append(r, generator);
+                if (!t)
+                        goto fail;
+                strv_free(r);
+                r = t;
+        }
+
         if (data_home) {
-                if (!(t = strv_append(r, data_home)))
+                t = strv_append(r, data_home);
+                if (!t)
                         goto fail;
                 strv_free(r);
                 r = t;
         }
 
         if (!strv_isempty(data_dirs)) {
-                if (!(t = strv_merge_concat(r, data_dirs, "/systemd/user")))
+                t = strv_merge_concat(r, data_dirs, "/systemd/user");
+                if (!t)
                         goto fail;
                 strv_free(r);
                 r = t;
         }
 
-        if (!(t = strv_merge(r, (char**) data_unit_paths)))
+        t = strv_merge(r, (char**) data_unit_paths);
+        if (!t)
                 goto fail;
         strv_free(r);
         r = t;
 
+        if (generator_late) {
+                t = strv_append(r, generator_late);
+                if (!t)
+                        goto fail;
+                strv_free(r);
+                r = t;
+        }
+
         if (!path_strv_make_absolute_cwd(r))
-            goto fail;
+                goto fail;
 
 finish:
         free(config_home);
@@ -182,7 +222,14 @@ fail:
         goto finish;
 }
 
-int lookup_paths_init(LookupPaths *p, ManagerRunningAs running_as, bool personal) {
+int lookup_paths_init(
+                LookupPaths *p,
+                ManagerRunningAs running_as,
+                bool personal,
+                const char *generator,
+                const char *generator_early,
+                const char *generator_late) {
+
         const char *e;
         char *t;
 
@@ -190,64 +237,83 @@ int lookup_paths_init(LookupPaths *p, ManagerRunningAs running_as, bool personal
 
         /* First priority is whatever has been passed to us via env
          * vars */
-        if ((e = getenv("SYSTEMD_UNIT_PATH")))
-                if (!(p->unit_path = path_split_and_make_absolute(e)))
+        e = getenv("SYSTEMD_UNIT_PATH");
+        if (e) {
+                p->unit_path = path_split_and_make_absolute(e);
+                if (!p->unit_path)
                         return -ENOMEM;
+        } else
+                p->unit_path = NULL;
 
         if (strv_isempty(p->unit_path)) {
-
                 /* Nothing is set, so let's figure something out. */
                 strv_free(p->unit_path);
 
+                /* For the user units we include share/ in the search
+                 * path in order to comply with the XDG basedir
+                 * spec. For the system stuff we avoid such
+                 * nonsense. OTOH we include /lib in the search path
+                 * for the system stuff but avoid it for user
+                 * stuff. */
+
                 if (running_as == MANAGER_USER) {
 
                         if (personal)
-                                p->unit_path = user_dirs();
+                                p->unit_path = user_dirs(generator, generator_early, generator_late);
                         else
                                 p->unit_path = strv_new(
                                                 /* If you modify this you also want to modify
                                                  * systemduserunitpath= in systemd.pc.in, and
                                                  * the arrays in user_dirs() above! */
+                                                STRV_IFNOTNULL(generator_early),
                                                 USER_CONFIG_UNIT_PATH,
                                                 "/etc/systemd/user",
                                                 "/run/systemd/user",
+                                                STRV_IFNOTNULL(generator),
                                                 "/usr/local/lib/systemd/user",
                                                 "/usr/local/share/systemd/user",
                                                 USER_DATA_UNIT_PATH,
                                                 "/usr/lib/systemd/user",
                                                 "/usr/share/systemd/user",
+                                                STRV_IFNOTNULL(generator_late),
                                                 NULL);
 
                         if (!p->unit_path)
                                 return -ENOMEM;
 
-                } else
-                        if (!(p->unit_path = strv_new(
-                                              /* If you modify this you also want to modify
-                                               * systemdsystemunitpath= in systemd.pc.in! */
-                                              SYSTEM_CONFIG_UNIT_PATH,
-                                              "/etc/systemd/system",
-                                              "/run/systemd/system",
-                                              "/usr/local/lib/systemd/system",
-                                              SYSTEM_DATA_UNIT_PATH,
-                                              "/usr/lib/systemd/system",
+                } else {
+                        p->unit_path = strv_new(
+                                        /* If you modify this you also want to modify
+                                         * systemdsystemunitpath= in systemd.pc.in! */
+                                        STRV_IFNOTNULL(generator_early),
+                                        SYSTEM_CONFIG_UNIT_PATH,
+                                        "/etc/systemd/system",
+                                        "/run/systemd/system",
+                                        STRV_IFNOTNULL(generator),
+                                        "/usr/local/lib/systemd/system",
+                                        SYSTEM_DATA_UNIT_PATH,
+                                        "/usr/lib/systemd/system",
 #ifdef HAVE_SPLIT_USR
-                                              "/lib/systemd/system",
+                                        "/lib/systemd/system",
 #endif
-                                              NULL)))
+                                        STRV_IFNOTNULL(generator_late),
+                                        NULL);
+
+                        if (!p->unit_path)
                                 return -ENOMEM;
+                }
         }
 
-        if (p->unit_path)
-                if (!path_strv_canonicalize(p->unit_path))
-                        return -ENOMEM;
+        if (!path_strv_canonicalize(p->unit_path))
+                return -ENOMEM;
 
         strv_uniq(p->unit_path);
         path_strv_remove_empty(p->unit_path);
 
         if (!strv_isempty(p->unit_path)) {
 
-                if (!(t = strv_join(p->unit_path, "\n\t")))
+                t = strv_join(p->unit_path, "\n\t");
+                if (!t)
                         return -ENOMEM;
                 log_debug("Looking for unit files in:\n\t%s", t);
                 free(t);
@@ -261,51 +327,58 @@ int lookup_paths_init(LookupPaths *p, ManagerRunningAs running_as, bool personal
 #ifdef HAVE_SYSV_COMPAT
                 /* /etc/init.d/ compatibility does not matter to users */
 
-                if ((e = getenv("SYSTEMD_SYSVINIT_PATH")))
-                        if (!(p->sysvinit_path = path_split_and_make_absolute(e)))
+                e = getenv("SYSTEMD_SYSVINIT_PATH");
+                if (e) {
+                        p->sysvinit_path = path_split_and_make_absolute(e);
+                        if (!p->sysvinit_path)
                                 return -ENOMEM;
+                } else
+                        p->sysvinit_path = NULL;
 
                 if (strv_isempty(p->sysvinit_path)) {
                         strv_free(p->sysvinit_path);
 
-                        if (!(p->sysvinit_path = strv_new(
-                                              SYSTEM_SYSVINIT_PATH,     /* /etc/init.d/ */
-                                              NULL)))
+                        p->sysvinit_path = strv_new(
+                                        SYSTEM_SYSVINIT_PATH,     /* /etc/init.d/ */
+                                        NULL);
+                        if (!p->sysvinit_path)
                                 return -ENOMEM;
                 }
 
-                if ((e = getenv("SYSTEMD_SYSVRCND_PATH")))
-                        if (!(p->sysvrcnd_path = path_split_and_make_absolute(e)))
+                e = getenv("SYSTEMD_SYSVRCND_PATH");
+                if (e) {
+                        p->sysvrcnd_path = path_split_and_make_absolute(e);
+                        if (!p->sysvrcnd_path)
                                 return -ENOMEM;
+                } else
+                        p->sysvrcnd_path = NULL;
 
                 if (strv_isempty(p->sysvrcnd_path)) {
                         strv_free(p->sysvrcnd_path);
 
-                        if (!(p->sysvrcnd_path = strv_new(
-                                              SYSTEM_SYSVRCND_PATH,     /* /etc/rcN.d/ */
-                                              NULL)))
+                        p->sysvrcnd_path = strv_new(
+                                        SYSTEM_SYSVRCND_PATH,     /* /etc/rcN.d/ */
+                                        NULL);
+                        if (!p->sysvrcnd_path)
                                 return -ENOMEM;
                 }
 
-                if (p->sysvinit_path)
-                        if (!path_strv_canonicalize(p->sysvinit_path))
-                                return -ENOMEM;
+                if (!path_strv_canonicalize(p->sysvinit_path))
+                        return -ENOMEM;
 
-                if (p->sysvrcnd_path)
-                        if (!path_strv_canonicalize(p->sysvrcnd_path))
-                                return -ENOMEM;
+                if (!path_strv_canonicalize(p->sysvrcnd_path))
+                        return -ENOMEM;
 
                 strv_uniq(p->sysvinit_path);
                 strv_uniq(p->sysvrcnd_path);
-
                 path_strv_remove_empty(p->sysvinit_path);
                 path_strv_remove_empty(p->sysvrcnd_path);
 
                 if (!strv_isempty(p->sysvinit_path)) {
 
-                        if (!(t = strv_join(p->sysvinit_path, "\n\t")))
+                        t = strv_join(p->sysvinit_path, "\n\t");
+                        if (!t)
                                 return -ENOMEM;
-
                         log_debug("Looking for SysV init scripts in:\n\t%s", t);
                         free(t);
                 } else {
@@ -316,7 +389,8 @@ int lookup_paths_init(LookupPaths *p, ManagerRunningAs running_as, bool personal
 
                 if (!strv_isempty(p->sysvrcnd_path)) {
 
-                        if (!(t = strv_join(p->sysvrcnd_path, "\n\t")))
+                        t = strv_join(p->sysvrcnd_path, "\n\t");
+                        if (!t)
                                 return -ENOMEM;
 
                         log_debug("Looking for SysV rcN.d links in:\n\t%s", t);
diff --git a/src/shared/path-lookup.h b/src/shared/path-lookup.h
index e8a5a77a7b..96c49c2400 100644
--- a/src/shared/path-lookup.h
+++ b/src/shared/path-lookup.h
@@ -34,7 +34,7 @@ typedef struct LookupPaths {
 
 int user_config_home(char **config_home);
 
-int lookup_paths_init(LookupPaths *p, ManagerRunningAs running_as, bool personal);
+int lookup_paths_init(LookupPaths *p, ManagerRunningAs running_as, bool personal, const char *generator, const char *generator_early, const char *generator_late);
 void lookup_paths_free(LookupPaths *p);
 
 #endif
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;
 
 }
diff --git a/src/shared/strv.h b/src/shared/strv.h
index afb31f385f..635e92b728 100644
--- a/src/shared/strv.h
+++ b/src/shared/strv.h
@@ -47,6 +47,10 @@ char **strv_uniq(char **l);
 char **strv_new(const char *x, ...) _sentinel_ _malloc_;
 char **strv_new_ap(const char *x, va_list ap) _malloc_;
 
+static inline const char* STRV_IFNOTNULL(const char *x) {
+        return x ? x : (const char *) -1;
+}
+
 static inline bool strv_isempty(char **l) {
         return !l || !*l;
 }