smack: introduce new mac_smack_copy() function

This adds a new mac_smack_copy() function in order to read the smack
label from the source and apply it to the destination.

src/basic/smack-util.c

@@ -185,6 +185,23 @@ int mac_smack_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
         return r;
 }
 
+int mac_smack_copy(const char *dest, const char *src) {
+        int r = 0;
+        _cleanup_free_ char *label = NULL;
+
+        assert(dest);
+        assert(src);
+
+        r = mac_smack_read(src, SMACK_ATTR_ACCESS, &label);
+        if (r < 0)
+                return r;
+
+        r = mac_smack_apply(dest, SMACK_ATTR_ACCESS, label);
+        if (r < 0)
+                return r;
+
+        return r;
+}
 
 #else
 bool mac_smack_use(void) {
@@ -214,4 +231,8 @@ int mac_smack_apply_pid(pid_t pid, const char *label) {
 int mac_smack_fix(const char *path, bool ignore_enoent, bool ignore_erofs) {
         return 0;
 }
+
+int mac_smack_copy(const char *dest, const char *src) {
+        return 0;
+}
 #endif

src/basic/smack-util.h

@@ -48,5 +48,5 @@ int mac_smack_read(const char *path, SmackAttr attr, char **label);
 int mac_smack_read_fd(int fd, SmackAttr attr, char **label);
 int mac_smack_apply(const char *path, SmackAttr attr, const char *label);
 int mac_smack_apply_fd(int fd, SmackAttr attr, const char *label);
-
 int mac_smack_apply_pid(pid_t pid, const char *label);
+int mac_smack_copy(const char *dest, const char *src);