bootspec: store 'root' field in each bootspec entry we load

This 'root' field contains the root path of the partition we found the
snippet in. The 'kernel', 'initrd', 'efi', … fields are relative to this
path.

This becomes particularly useful later when we add support for loading
snippets from both the ESP and XBOOTLDR, but already simplifies the code
for us a bit in systemctl.

src/shared/bootspec.c

@@ -27,6 +27,7 @@ static void boot_entry_free(BootEntry *entry) {
 
         free(entry->id);
         free(entry->path);
+        free(entry->root);
         free(entry->title);
         free(entry->show_title);
         free(entry->version);
@@ -39,13 +40,18 @@ static void boot_entry_free(BootEntry *entry) {
         free(entry->device_tree);
 }
 
-static int boot_entry_load(const char *path, BootEntry *entry) {
+static int boot_entry_load(
+                const char *root,
+                const char *path,
+                BootEntry *entry) {
+
         _cleanup_(boot_entry_free) BootEntry tmp = {};
         _cleanup_fclose_ FILE *f = NULL;
         unsigned line = 1;
         char *b, *c;
         int r;
 
+        assert(root);
         assert(path);
         assert(entry);
 
@@ -62,6 +68,10 @@ static int boot_entry_load(const char *path, BootEntry *entry) {
         if (!tmp.path)
                 return log_oom();
 
+        tmp.root = strdup(root);
+        if (!tmp.root)
+                return log_oom();
+
         f = fopen(path, "re");
         if (!f)
                 return log_error_errno(errno, "Failed to open \"%s\": %m", path);
@@ -215,13 +225,19 @@ static int boot_entry_compare(const BootEntry *a, const BootEntry *b) {
         return str_verscmp(a->id, b->id);
 }
 
-static int boot_entries_find(const char *dir, BootEntry **ret_entries, size_t *ret_n_entries) {
+static int boot_entries_find(
+                const char *root,
+                const char *dir,
+                BootEntry **ret_entries,
+                size_t *ret_n_entries) {
+
         _cleanup_strv_free_ char **files = NULL;
         char **f;
         int r;
         BootEntry *array = NULL;
         size_t n_allocated = 0, n = 0;
 
+        assert(root);
         assert(dir);
         assert(ret_entries);
         assert(ret_n_entries);
@@ -234,7 +250,7 @@ static int boot_entries_find(const char *dir, BootEntry **ret_entries, size_t *r
                 if (!GREEDY_REALLOC0(array, n_allocated, n + 1))
                         return log_oom();
 
-                r = boot_entry_load(*f, array + n);
+                r = boot_entry_load(root, *f, array + n);
                 if (r < 0)
                         continue;
 
@@ -369,7 +385,7 @@ int boot_entries_load_config(const char *esp_path, BootConfig *config) {
                 return r;
 
         p = strjoina(esp_path, "/loader/entries");
-        r = boot_entries_find(p, &config->entries, &config->n_entries);
+        r = boot_entries_find(esp_path, p, &config->entries, &config->n_entries);
         if (r < 0)
                 return r;
 
@@ -799,7 +815,6 @@ found:
 
 int find_default_boot_entry(
                 const char *esp_path,
-                char **esp_where,
                 BootConfig *config,
                 const BootEntry **e) {
 
@@ -824,8 +839,5 @@ int find_default_boot_entry(
         *e = &config->entries[config->default_entry];
         log_debug("Found default boot entry in file \"%s\"", (*e)->path);
 
-        if (esp_where)
-                *esp_where = TAKE_PTR(where);
-
         return 0;
 }