shared/install: fix bogus error handling

This partially reverts a4f0e0da35. The
intent was good, we gather the errors, but we have no mechanism to
propagate the result, so the gathered result was ignored. In 'changes'
we can only report errors for specific units. If reading of the
directory fails, we might just as well report the error immediately.
This isn't great, but it's better then ignoring the errors. In practice,
failing halfway in this manner is unlikely, since it'd mean that the fs
is corrupted or something like that. We might as well return immediately
on such catastrophic errors.

src/shared/install.c

@@ -370,6 +370,24 @@ static void install_change_dump_success(const InstallChange *change) {
         }
 }
 
+/* Generated/transient/missing/invalid units when applying presets.
+ * Coordinate with install_change_dump_error() below. */
+static bool ERRNO_IS_NEG_UNIT_ISSUE(intmax_t r) {
+        return IN_SET(r,
+                      -EEXIST,
+                      -ERFKILL,
+                      -EADDRNOTAVAIL,
+                      -ETXTBSY,
+                      -EBADSLT,
+                      -EIDRM,
+                      -EUCLEAN,
+                      -ELOOP,
+                      -EXDEV,
+                      -ENOENT,
+                      -ENOLINK,
+                      -EUNATCH);
+}
+
 int install_change_dump_error(const InstallChange *change, char **ret_errmsg, const char **ret_bus_error) {
         char *m;
         const char *bus_error;
@@ -3609,6 +3627,7 @@ static int preset_prepare_one(
                                   &info, changes, n_changes);
         if (r < 0)
                 return r;
+
         if (!streq(name, info->name)) {
                 log_debug("Skipping %s because it is an alias for %s.", name, info->name);
                 return 0;
@@ -3710,19 +3729,19 @@ int unit_file_preset_all(
         if (r < 0)
                 return r;
 
-        r = 0;
         STRV_FOREACH(i, lp.search_path) {
                 _cleanup_closedir_ DIR *d = NULL;
 
                 d = opendir(*i);
                 if (!d) {
-                        if (errno != ENOENT)
-                                RET_GATHER(r, -errno);
-                        continue;
+                        if (errno == ENOENT)
+                                continue;
+
+                        return log_debug_errno(errno, "Failed to opendir %s: %m", *i);
                 }
 
-                FOREACH_DIRENT(de, d, RET_GATHER(r, -errno)) {
-                        int k;
+                FOREACH_DIRENT(de, d,
+                               return log_debug_errno(errno, "Failed to read directory %s: %m", *i)) {
 
                         if (!unit_name_is_valid(de->d_name, UNIT_NAME_ANY))
                                 continue;
@@ -3730,23 +3749,9 @@ int unit_file_preset_all(
                         if (!IN_SET(de->d_type, DT_LNK, DT_REG))
                                 continue;
 
-                        k = preset_prepare_one(scope, &plus, &minus, &lp, de->d_name, &presets, changes, n_changes);
-                        if (k < 0 &&
-                            !IN_SET(k, -EEXIST,
-                                       -ERFKILL,
-                                       -EADDRNOTAVAIL,
-                                       -ETXTBSY,
-                                       -EBADSLT,
-                                       -EIDRM,
-                                       -EUCLEAN,
-                                       -ELOOP,
-                                       -EXDEV,
-                                       -ENOENT,
-                                       -ENOLINK,
-                                       -EUNATCH))
-                                /* Ignore generated/transient/missing/invalid units when applying preset, propagate other errors.
-                                 * Coordinate with install_change_dump_error() above. */
-                                RET_GATHER(r, k);
+                        r = preset_prepare_one(scope, &plus, &minus, &lp, de->d_name, &presets, changes, n_changes);
+                        if (r < 0 && !ERRNO_IS_NEG_UNIT_ISSUE(r))
+                                return r;
                 }
         }