logind: also cache LoaderEntryOneShot EFI variable

With this we are now caching all EFI variables that we expose as
property in logind. Thus a client invoking GetAllProperties() should
only trgger a single read of each variable, but never repeated ones.

Obsoletes: #16190
Fixes: #14828

src/shared/efi-loader.c

@@ -772,3 +772,35 @@ int efi_loader_get_config_timeout_one_shot(usec_t *ret) {
         *ret = cache = sec * USEC_PER_SEC; /* return in µs */
         return 0;
 }
+
+int efi_loader_update_entry_one_shot_cache(char **cache, struct stat *cache_stat) {
+        _cleanup_free_ char *fn = NULL, *v = NULL;
+        struct stat new_stat;
+        int r;
+
+        assert(cache);
+        assert(cache_stat);
+
+        fn = efi_variable_path(EFI_VENDOR_LOADER, "LoaderEntryOneShot");
+        if (!fn)
+                return -ENOMEM;
+
+        /* stat() the EFI variable, to see if the mtime changed. If it did we need to cache again. */
+        if (stat(fn, &new_stat) < 0)
+                return -errno;
+
+        if (stat_inode_unmodified(&new_stat, cache_stat))
+                return 0;
+
+        r = efi_get_variable_string(EFI_VENDOR_LOADER, "LoaderEntryOneShot", &v);
+        if (r < 0)
+                return r;
+
+        if (!efi_loader_entry_name_valid(v))
+                return -EINVAL;
+
+        *cache_stat = new_stat;
+        free_and_replace(*cache, v);
+
+        return 0;
+}

src/shared/efi-loader.h

@@ -3,6 +3,8 @@
 
 #include "efivars.h"
 
+#include <sys/stat.h>
+
 #if ENABLE_EFI
 
 int efi_reboot_to_firmware_supported(void);
@@ -24,6 +26,7 @@ int efi_loader_get_entries(char ***ret);
 int efi_loader_get_features(uint64_t *ret);
 
 int efi_loader_get_config_timeout_one_shot(usec_t *ret);
+int efi_loader_update_entry_one_shot_cache(char **cache, struct stat *cache_stat);
 
 #else
 
@@ -83,6 +86,10 @@ static inline int efi_loader_get_config_timeout_one_shot(usec_t *ret) {
         return -EOPNOTSUPP;
 }
 
+static inline int efi_loader_update_entry_one_shot_cache(char **cache, struct stat *cache_stat) {
+        return -EOPNOTSUPP;
+}
+
 #endif
 
 bool efi_loader_entry_name_valid(const char *s);