shared/install,systemctl,core: report offending file on installation error

Fixes #2191:

$ systemctl --root=/ enable sddm
Created symlink /etc/systemd/system/display-manager.service, pointing to /usr/lib/systemd/system/sddm.service.
$ sudo build/systemctl --root=/ enable gdm
Failed to enable unit, file /etc/systemd/system/display-manager.service already exists and is a symlink to /usr/lib/systemd/system/sddm.service.
$ sudo build/systemctl --root= enable sddm
$ sudo build/systemctl --root= enable gdm
Failed to enable unit: File /etc/systemd/system/display-manager.service already exists and is a symlink to /usr/lib/systemd/system/sddm.service.

(I tried a few different approaches to pass the error information back to the
caller. Adding a new parameter to hold the error results in a gigantic patch
and a lot of hassle to pass the args arounds. Adding this information to the
changes array is straightforward and can be more easily extended in the
future.)

In case local installation is performed, the full set of errors can be reported
and we do that. When running over dbus, only the first error is reported.

3 files changed, 116 insertions, 32 deletions

diff --git a/src/shared/bus-util.c b/src/shared/bus-util.c
index 677970b7f0..6a1877d8aa 100644
--- a/src/shared/bus-util.c
+++ b/src/shared/bus-util.c
@@ -2200,20 +2200,16 @@ int bus_deserialize_and_dump_unit_file_changes(sd_bus_message *m, bool quiet, Un
                 return bus_log_parse_error(r);
 
         while ((r = sd_bus_message_read(m, "(sss)", &type, &path, &source)) > 0) {
-                if (!quiet) {
-                        if (streq(type, "symlink"))
-                                log_info("Created symlink from %s to %s.", path, source);
-                        else if (streq(type, "unlink"))
-                                log_info("Removed symlink %s.", path);
-                        else if (streq(type, "masked"))
-                                log_info("Unit %s is masked, ignoring.", path);
-                        else
-                                log_notice("Manager reported unknown change type \"%s\" for %s.", type, path);
+                /* We expect only "success" changes to be sent over the bus.
+                   Hence, reject anything negative. */
+                UnitFileChangeType ch = unit_file_change_type_from_string(type);
+
+                if (ch < 0) {
+                        log_notice("Manager reported unknown change type \"%s\" for path \"%s\", ignoring.", type, path);
+                        continue;
                 }
 
-                r = unit_file_changes_add(changes, n_changes,
-                                          unit_file_change_type_from_string(type),
-                                          path, source);
+                r = unit_file_changes_add(changes, n_changes, ch, path, source);
                 if (r < 0)
                         return r;
         }
@@ -2224,6 +2220,7 @@ int bus_deserialize_and_dump_unit_file_changes(sd_bus_message *m, bool quiet, Un
         if (r < 0)
                 return bus_log_parse_error(r);
 
+        unit_file_dump_changes(0, NULL, *changes, *n_changes, false);
         return 0;
 }
 
diff --git a/src/shared/install.c b/src/shared/install.c
index 1522435f7f..febe33ed7b 100644
--- a/src/shared/install.c
+++ b/src/shared/install.c
@@ -276,6 +276,70 @@ void unit_file_changes_free(UnitFileChange *changes, unsigned n_changes) {
         free(changes);
 }
 
+void unit_file_dump_changes(int r, const char *verb, const UnitFileChange *changes, unsigned n_changes, bool quiet) {
+        unsigned i;
+        bool logged = false;
+
+        assert(changes || n_changes == 0);
+        /* If verb is not specified, errors are not allowed! */
+        assert(verb || r >= 0);
+
+        for (i = 0; i < n_changes; i++) {
+                assert(verb || changes[i].type >= 0);
+
+                switch(changes[i].type) {
+                case UNIT_FILE_SYMLINK:
+                        if (!quiet)
+                                log_info("Created symlink %s, pointing to %s.", changes[i].path, changes[i].source);
+                        break;
+                case UNIT_FILE_UNLINK:
+                        if (!quiet)
+                                log_info("Removed %s.", changes[i].path);
+                        break;
+                case UNIT_FILE_IS_MASKED:
+                        if (!quiet)
+                                log_info("Unit %s is masked, ignoring.", changes[i].path);
+                        break;
+                case -EEXIST:
+                        if (changes[i].source)
+                                log_error_errno(changes[i].type,
+                                                "Failed to %s unit, file %s already exists and is a symlink to %s.",
+                                                verb, changes[i].path, changes[i].source);
+                        else
+                                log_error_errno(changes[i].type,
+                                                "Failed to %s unit, file %s already exists.",
+                                                verb, changes[i].path);
+                        logged = true;
+                        break;
+                case -ERFKILL:
+                        log_error_errno(changes[i].type, "Failed to %s unit, unit %s is masked.",
+                                        verb, changes[i].path);
+                        logged = true;
+                        break;
+                case -EADDRNOTAVAIL:
+                        log_error_errno(changes[i].type, "Failed to %s unit, unit %s is transient or generated.",
+                                        verb, changes[i].path);
+                        logged = true;
+                        break;
+                case -ELOOP:
+                        log_error_errno(changes[i].type, "Failed to %s unit, refusing to operate on linked unit file %s",
+                                        verb, changes[i].path);
+                        logged = true;
+                        break;
+                default:
+                        assert(changes[i].type < 0);
+                        log_error_errno(changes[i].type, "Failed to %s unit, file %s: %m.",
+                                        verb, changes[i].path);
+                        logged = true;
+                }
+        }
+
+        if (r < 0 && !logged)
+                log_error_errno(r, "Failed to %s: %m.", verb);
+}
+
+
+
 static int create_symlink(
                 const char *old_path,
                 const char *new_path,
@@ -300,8 +364,10 @@ static int create_symlink(
                 return 1;
         }
 
-        if (errno != EEXIST)
+        if (errno != EEXIST) {
+                unit_file_changes_add(changes, n_changes, -errno, new_path, NULL);
                 return -errno;
+        }
 
         r = readlink_malloc(new_path, &dest);
         if (r < 0)
@@ -310,8 +376,10 @@ static int create_symlink(
         if (path_equal(dest, old_path))
                 return 0;
 
-        if (!force)
+        if (!force) {
+                unit_file_changes_add(changes, n_changes, -EEXIST, new_path, dest);
                 return -EEXIST;
+        }
 
         r = symlink_atomic(old_path, new_path);
         if (r < 0)
@@ -421,6 +489,7 @@ static int remove_marked_symlinks_fd(
                         p = path_make_absolute(de->d_name, path);
                         if (!p)
                                 return -ENOMEM;
+                        path_kill_slashes(p);
 
                         q = readlink_malloc(p, &dest);
                         if (q == -ENOENT)
@@ -444,10 +513,10 @@ static int remove_marked_symlinks_fd(
                         if (unlinkat(fd, de->d_name, 0) < 0 && errno != ENOENT) {
                                 if (r == 0)
                                         r = -errno;
+                                unit_file_changes_add(changes, n_changes, -errno, p, NULL);
                                 continue;
                         }
 
-                        path_kill_slashes(p);
                         (void) rmdir_parents(p, config_path);
 
                         unit_file_changes_add(changes, n_changes, UNIT_FILE_UNLINK, p, NULL);
@@ -745,19 +814,26 @@ static UnitFileInstallInfo *install_info_find(InstallContext *c, const char *nam
         return ordered_hashmap_get(c->will_process, name);
 }
 
-static int install_info_may_process(UnitFileInstallInfo *i, const LookupPaths *paths) {
+static int install_info_may_process(
+                UnitFileInstallInfo *i,
+                const LookupPaths *paths,
+                UnitFileChange **changes,
+                unsigned *n_changes) {
         assert(i);
         assert(paths);
 
         /* Checks whether the loaded unit file is one we should process, or is masked, transient or generated and thus
          * not subject to enable/disable operations. */
 
-        if (i->type == UNIT_FILE_TYPE_MASKED)
+        if (i->type == UNIT_FILE_TYPE_MASKED) {
+                unit_file_changes_add(changes, n_changes, -ERFKILL, i->path, NULL);
                 return -ERFKILL;
-        if (path_is_generator(paths, i->path))
-                return -EADDRNOTAVAIL;
-        if (path_is_transient(paths, i->path))
+        }
+        if (path_is_generator(paths, i->path) ||
+            path_is_transient(paths, i->path)) {
+                unit_file_changes_add(changes, n_changes, -EADDRNOTAVAIL, i->path, NULL);
                 return -EADDRNOTAVAIL;
+        }
 
         return 0;
 }
@@ -1637,8 +1713,11 @@ int unit_file_unmask(
                         return -ENOMEM;
 
                 if (unlink(path) < 0) {
-                        if (errno != ENOENT && r >= 0)
-                                r = -errno;
+                        if (errno != ENOENT) {
+                                if (r >= 0)
+                                        r = -errno;
+                                unit_file_changes_add(changes, n_changes, -errno, path, NULL);
+                        }
 
                         continue;
                 }
@@ -1953,7 +2032,7 @@ int unit_file_add_dependency(
         r = install_info_discover(scope, &c, &paths, target, SEARCH_FOLLOW_CONFIG_SYMLINKS, &target_info);
         if (r < 0)
                 return r;
-        r = install_info_may_process(target_info, &paths);
+        r = install_info_may_process(target_info, &paths, changes, n_changes);
         if (r < 0)
                 return r;
 
@@ -1965,7 +2044,7 @@ int unit_file_add_dependency(
                 r = install_info_discover(scope, &c, &paths, *f, SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
                 if (r < 0)
                         return r;
-                r = install_info_may_process(i, &paths);
+                r = install_info_may_process(i, &paths, changes, n_changes);
                 if (r < 0)
                         return r;
 
@@ -2018,7 +2097,7 @@ int unit_file_enable(
                 r = install_info_discover(scope, &c, &paths, *f, SEARCH_LOAD, &i);
                 if (r < 0)
                         return r;
-                r = install_info_may_process(i, &paths);
+                r = install_info_may_process(i, &paths, changes, n_changes);
                 if (r < 0)
                         return r;
 
@@ -2131,7 +2210,7 @@ int unit_file_set_default(
         r = install_info_discover(scope, &c, &paths, name, 0, &i);
         if (r < 0)
                 return r;
-        r = install_info_may_process(i, &paths);
+        r = install_info_may_process(i, &paths, changes, n_changes);
         if (r < 0)
                 return r;
 
@@ -2163,7 +2242,7 @@ int unit_file_get_default(
         r = install_info_discover(scope, &c, &paths, SPECIAL_DEFAULT_TARGET, SEARCH_FOLLOW_CONFIG_SYMLINKS, &i);
         if (r < 0)
                 return r;
-        r = install_info_may_process(i, &paths);
+        r = install_info_may_process(i, &paths, NULL, 0);
         if (r < 0)
                 return r;
 
@@ -2425,7 +2504,9 @@ static int preset_prepare_one(
                 InstallContext *minus,
                 LookupPaths *paths,
                 UnitFilePresetMode mode,
-                const char *name) {
+                const char *name,
+                UnitFileChange **changes,
+                unsigned *n_changes) {
 
         UnitFileInstallInfo *i;
         int r;
@@ -2443,7 +2524,7 @@ static int preset_prepare_one(
                 if (r < 0)
                         return r;
 
-                r = install_info_may_process(i, paths);
+                r = install_info_may_process(i, paths, changes, n_changes);
                 if (r < 0)
                         return r;
         } else
@@ -2482,7 +2563,7 @@ int unit_file_preset(
                 if (!unit_name_is_valid(*i, UNIT_NAME_ANY))
                         return -EINVAL;
 
-                r = preset_prepare_one(scope, &plus, &minus, &paths, mode, *i);
+                r = preset_prepare_one(scope, &plus, &minus, &paths, mode, *i, changes, n_changes);
                 if (r < 0)
                         return r;
         }
@@ -2537,7 +2618,8 @@ int unit_file_preset_all(
                         if (!IN_SET(de->d_type, DT_LNK, DT_REG))
                                 continue;
 
-                        r = preset_prepare_one(scope, &plus, &minus, &paths, mode, de->d_name);
+                        /* we don't pass changes[] in, because we want to handle errors on our own */
+                        r = preset_prepare_one(scope, &plus, &minus, &paths, mode, de->d_name, NULL, 0);
                         if (r == -ERFKILL)
                                 r = unit_file_changes_add(changes, n_changes,
                                                           UNIT_FILE_IS_MASKED, de->d_name, NULL);
diff --git a/src/shared/install.h b/src/shared/install.h
index 219b48f428..82c62095d5 100644
--- a/src/shared/install.h
+++ b/src/shared/install.h
@@ -77,8 +77,12 @@ enum UnitFileChangeType {
         _UNIT_FILE_CHANGE_TYPE_INVALID = -1
 };
 
+/* type can either one of the UnitFileChangeTypes listed above, or a negative error.
+ * If source is specified, it should be the contents of the path symlink.
+ * In case of an error, source should be the existing symlink contents or NULL
+ */
 struct UnitFileChange {
-        UnitFileChangeType type;
+        int type; /* UnitFileChangeType or bust */
         char *path;
         char *source;
 };
@@ -233,6 +237,7 @@ Hashmap* unit_file_list_free(Hashmap *h);
 
 int unit_file_changes_add(UnitFileChange **changes, unsigned *n_changes, UnitFileChangeType type, const char *path, const char *source);
 void unit_file_changes_free(UnitFileChange *changes, unsigned n_changes);
+void unit_file_dump_changes(int r, const char *verb, const UnitFileChange *changes, unsigned n_changes, bool quiet);
 
 int unit_file_query_preset(UnitFileScope scope, const char *root_dir, const char *name);