support: Add <support/readdir.h>

It allows to read directories using the six readdir variants
without writing type-specific code or using skeleton files
that are compiled four times.

The readdir_r subtest for support_readdir_expect_error revealed
bug 32124.

Reviewed-by: DJ Delorie <dj@redhat.com>

1 files changed, 85 insertions, 0 deletions

diff --git a/support/readdir.h b/support/readdir.h
new file mode 100644
index 0000000000..7d7c7650d4
--- /dev/null
+++ b/support/readdir.h
@@ -0,0 +1,85 @@
+/* Type-generic wrapper for readdir functions.
+   Copyright (C) 2024 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#ifndef SUPPORT_READDIR_H
+#define SUPPORT_READDIR_H
+
+#include <dirent.h>
+#include <stdbool.h>
+#include <stdint.h>
+
+__BEGIN_DECLS
+
+/* Definition independent of _FILE_OFFSET_BITS.  */
+struct support_dirent
+{
+  uint64_t d_ino;
+  uint64_t d_off;               /* 0 if d_off is not supported.  */
+  uint32_t d_type;
+  char *d_name;
+};
+
+/* Operation to be performed by support_readdir below.  */
+enum support_readdir_op
+  {
+    SUPPORT_READDIR,
+    SUPPORT_READDIR64,
+    SUPPORT_READDIR_R,
+    SUPPORT_READDIR64_R,
+    SUPPORT_READDIR64_COMPAT,
+    SUPPORT_READDIR64_R_COMPAT,
+  };
+
+/* Returns the last supported function.  May exclude
+   SUPPORT_READDIR64_R_COMPAT if not implemented.  */
+enum support_readdir_op support_readdir_op_last (void);
+
+/* Returns the name of the function that corresponds to the OP constant.  */
+const char *support_readdir_function (enum support_readdir_op op);
+
+/* Returns the d_ino field width for OP, in bits.  */
+unsigned int support_readdir_inode_width (enum support_readdir_op op);
+
+/* Returns the d_off field width for OP, in bits.  Zero if not present.  */
+unsigned int support_readdir_offset_width (enum support_readdir_op op);
+
+/* Returns true if OP is an _r variant with name length restrictions.  */
+bool support_readdir_r_variant (enum support_readdir_op op);
+
+/* First, free E->d_name and set the field to NULL.  Then call the
+   readdir variant as specified by OP.  If successfully, copy fields
+   to E, make a copy of the entry name using strdup, and write its
+   addres sto E->d_name.
+
+   Return true if an entry was read, or false if the end of the
+   directory stream was reached.  Terminates the process upon error.
+   The caller is expected to free E->d_name if the function is not
+   called again for this E.
+
+   Note that this function assumes that E->d_name has been initialized
+   to NULL or has been allocated by a previous call to this function.  */
+bool support_readdir (DIR *stream, enum support_readdir_op op,
+                      struct support_dirent *e) __nonnull ((1, 3));
+
+/* Checks that the readdir operation OP fails with errno value EXPECTED.  */
+void support_readdir_expect_error (DIR *stream, enum support_readdir_op op,
+                                   int expected) __nonnull ((1));
+
+__END_DECLS
+
+#endif /* SUPPORT_READDIR_H */