shared/bootspec: remember the full path to boot entry and use it in logging

It's much easier to understand what is going on when the full path is
logged.

src/shared/bootspec.c

@@ -24,6 +24,7 @@ void boot_entry_free(BootEntry *entry) {
         assert(entry);
 
         free(entry->id);
+        free(entry->path);
         free(entry->title);
         free(entry->show_title);
         free(entry->version);
@@ -57,6 +58,10 @@ int boot_entry_load(const char *path, BootEntry *entry) {
         if (!tmp.id)
                 return log_oom();
 
+        tmp.path = strdup(path);
+        if (!tmp.path)
+                return log_oom();
+
         f = fopen(path, "re");
         if (!f)
                 return log_error_errno(errno, "Failed to open \"%s\": %m", path);
@@ -625,6 +630,7 @@ 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);

src/shared/bootspec.h

@@ -9,7 +9,8 @@
 #include "sd-id128.h"
 
 typedef struct BootEntry {
-        char *id;
+        char *id;       /* This is the file basename without extension */
+        char *path;     /* This is the full path to the file */
         char *title;
         char *show_title;
         char *version;