guestfs_readlinklist: Reimplement to avoid protocol limits.

TODO

@@ -564,5 +564,3 @@ These would be changed from daemon_functions to non_daemon_functions,
 with the non-daemon versions implemented using guestfs_upload and
 guestfs_download (and others).  This change should be transparent from
 the p.o.v of the API and ABI.
-
- - guestfs_readlinklist

daemon/link.c

@@ -53,7 +53,7 @@ do_readlink (const char *path)
 }
 
 char **
-do_readlinklist (const char *path, char *const *names)
+do_internal_readlinklist (const char *path, char *const *names)
 {
   int fd_cwd;
   size_t i;

generator/generator_actions.ml

@@ -2196,6 +2196,29 @@ list a directory contents without making many round-trips.
 See also C<guestfs_lstatlist> for a similarly efficient call
 for getting standard stats." };
 
+  { defaults with
+    name = "readlinklist";
+    style = RStringList "links", [Pathname "path"; StringList "names"], [];
+    shortdesc = "readlink on multiple files";
+    longdesc = "\
+This call allows you to do a C<readlink> operation
+on multiple files, where all files are in the directory C<path>.
+C<names> is the list of files from this directory.
+
+On return you get a list of strings, with a one-to-one
+correspondence to the C<names> list.  Each string is the
+value of the symbolic link.
+
+If the C<readlink(2)> operation fails on any name, then
+the corresponding result string is the empty string C<\"\">.
+However the whole operation is completed even if there
+were C<readlink(2)> errors, and so you can call this
+function with names where you don't know if they are
+symbolic links already (albeit slightly less efficient).
+
+This call is intended for programs that want to efficiently
+list a directory contents without making many round-trips." };
+
 ]
 
 (* daemon_functions are any functions which cause some action
@@ -6379,9 +6402,10 @@ this call to fail.  The caller must split up such requests
 into smaller groups of names." };
 
   { defaults with
-    name = "readlinklist";
+    name = "internal_readlinklist";
     style = RStringList "links", [Pathname "path"; StringList "names"], [];
     proc_nr = Some 206;
+    in_docs = false; in_fish = false;
     shortdesc = "readlink on multiple files";
     longdesc = "\
 This call allows you to do a C<readlink> operation

src/file.c

@@ -494,3 +494,44 @@ guestfs__lxattrlist (guestfs_h *g, const char *dir, char *const *names)
 
   return ret;
 }
+
+#define READLINK_MAX 1000
+
+char **
+guestfs__readlinklist (guestfs_h *g, const char *dir, char *const *names)
+{
+  size_t len = count_strings (names);
+  char **first;
+  size_t old_len, ret_len = 0;
+  char **ret = NULL, **links;
+
+  while (len > 0) {
+    first = take_strings (g, names, READLINK_MAX, &names);
+    len = len <= READLINK_MAX ? 0 : len - READLINK_MAX;
+
+    links = guestfs_internal_readlinklist (g, dir, first);
+    /* Note we don't need to free up the strings because take_strings
+     * does not do a deep copy.
+     */
+    free (first);
+
+    if (links == NULL) {
+      guestfs___free_string_list (ret);
+      return NULL;
+    }
+
+    /* Append links to ret. */
+    old_len = ret_len;
+    ret_len += count_strings (links);
+    ret = safe_realloc (g, ret, ret_len * sizeof (char *));
+    memcpy (&ret[old_len], links, (ret_len-old_len) * sizeof (char *));
+
+    free (links);
+  }
+
+  /* NULL-terminate the list. */
+  ret = safe_realloc (g, ret, (ret_len+1) * sizeof (char *));
+  ret[ret_len] = NULL;
+
+  return ret;
+}